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Important Questions Class 10 Science Chapter 9 Heredity And Evolution

All Heredity And Evolution Class 10 Science Important Questions provided below have been prepared by expert teachers of Standard 10 Science. Please learn them and let us know if you have any questions.

Very Short Answer:

Question. What is heredity?
Answer: The inheritance of characters (or traits) from the parents to their offisprings is called heredity.

Question. Why is the progeny always tall when a tall pea plant is crossed with a short pea plant?
Answer: When a tall pea plant is crossed with a short pea plant, the resultant progeny is always tall because tall is dominant trait and short is recessive trait. Therefore, dominant trait expresses itself in the progeny.

Question. What is meant by analogous organs? Taking a suitable example, explain how they support the theory of Organic Evolution.
Answer. Analogous organs are those organs which I have different basic structural design and developmental origin but have similar appearance and perform similar functions.
Example: The wings of birds and bats look similar but have different design in their structure. 
They have a common function of flying but their origins are not common. So, birds and bats are not closely related.

Question. What is a gene?
Answer. Gene is the unit of inheritance. Gene is the part of a chromosome which controls the appearance of a set of hereditary characteristics.

Question. “The sex of the children is determined by what they inherit from their father and not their mother.” Justify.
Answer. It is because a child who inherits an X chromosome from her father will be a girl and one who inherits a Y chromosome from his father will be a boy. But all children inherit a X chromosome from their mother regardless of whether they are boys or girls.

Question. What is a sex chromosome?
Answer. Sex chromosome is a chromosome that operates in the sex-determining mechanism of a species. Many animals have two different types of sex chromosomes. For example, in human there is a large X chromosome and a much smaller Y chromosome.

Question. Describe briefly four ways in which individuals with a particular trait may increase in a population.
Answer. The four ways in which individuals with a particular trait may increase in a population are as follows:
a) Sexual reproduction results into variations.
b) The individuals with special traits survive the attack of their predators and multiply while the other will perish.
c) Genetic drift provides diversity without any adaptation.
d) Variations in the species may lead to increased survival of the individuals.

Question. Define variation in relation to a species. Why is variation beneficial to the species?
Answer. Variation refers to the differences in the characters or traits among the individuals of a species. Variations are beneficial to the species because:
a) They enable the organisms to adapt themselves in changing environment.
b) Variations form the basis of heredity.
c) They form the raw materials for evolution and development of new species.

Question. The human beings who look so different from each other in terms of colour, size and looks are said to belong to the same species. Why? Justify your answer.
Answer. Human beings are said to belong to the same species because of the following reasons:
DNA studies. Number of chromosome is same, All have a common ancestor.
They interbreed among themselves to produce fertile young ones of their own kind.

Question. Distinguish between acquired and inherited traits by giving one example of each. Why are traits acquired during the lifetime of an individual not inherited?
Answer. Acquired trait is a particular characteristic that is developed during the lifetime of an individual. Such characteristics are not genetically controlled and cannot be passed on to the next generation. Example: Loss of weight due to starvation.
Inherited trait is the transmission of particular characteristics from parents to their off springs, generation to generation. Such traits are genetically determined characteristic that distinguishes a person. 
Example: Colour of skin.
The acquired traits cannot change the DNA of the germ cells. Therefore, the acquired traits cannot be inherited over generations during the lifetime of an individual.

Question. What is the effect of DNA copying which is not perfectly accurate in the reproduction process?
Answer: DNA copying is imperative for reproduction and multiplication of species. When a cell or an organism is ready to reproduce asexually it makes a copy of its DNA which carries all the hereditary information in the form of genes. In most cases, DNA copying is accurate and progenies are exact copies of parents but very rarely error takes place during this process and variations arise among the individuals of progeny. In sexually reproducing organisms, error in DNA copying accounts for variations during gametogenesis along with variation that always arise due to crossing over during meiotic divisions.

Question. Name the information source for making proteins in the cells. 
Answer: Deoxyribonucleic acid (DNA) present in the chromosomes of cell nucleus is the information source for making proteins.

Question. Distinguish between the acquired traits and the inherited traits in tabular form, giving one example for each. 
Answer: Differences between the inherited traits and acquired traits are as follows :

Question. All the variations in a species do not have equal chances of survival. Why?
Answer: All the variations do not have equal chances of survival in the environment in which they live. Depending on the nature of variations, different individuals would have different kinds of advantages. The organisms which are most adapted to the environment will survive.

Question. What is a gene?
Answer: A gene is a unit of DNA on a chromosome which governs the synthesis of particular protein that controls specific characteristics (or traits) of an organism.

Question. What is speciation?
Answer: The process by which new species develop from the existing species is known as speciation.

Question. Give the respective scientific terms used for studying
(a) the mechanism by which variations are created and inherited and
(b) the development of new type of organisms from the existing ones.
Answer: (a) Heredity is the mechanism by which variations are created and inherited.
(b) Evolution is the process in which development of new type of organisms takes place from the existing ones.

Question. Write the contribution of Charles Darwin in the field of ‘evolution’. 
Answer: The contribution of Charles Darwin in the field of evolution is that only the organism which can adapt to the changing environmental conditions can survive and he also stated that the natural selection is a process which plays an important role in evolution of plants and animals by selecting the organisms with traits favourable to the environment.

Question: Give one example each of characters that are inherited and the ones that are acquired in
humans. Mention the difference between the inherited and the acquired characters.
Answer. Eye colour or hair colour of a person is an example of inherited character whereas, body weight is an example of acquired character.
The basic difference between inherited and acquired character is that inherited character is passed on from parent to offspring and acquired characters are acquired by an individual during his lifetime depending upon his lifestyle.

Question: How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer. During sexual reproduction, a female gamete or egg cell fuses with a male gamete or sperm cell which are haploid to form zygote. Zygote is diploid which contains 23 chromosomes from mother and 23 from father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.

Question: Explain the mechanism of sex determination in humans.
                                            Or
With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of sex of a child?
Answer. Mechanism of Sex Determination in Human Beings:
In human beings, the sex of the individual is genetically determined.
• Sex determination is the process by which sex of a new born individual can be determined.
• Human beings have 1 unpaired sex chromosome. Sex chromosome of male is XY and of female is XX.
• Sex of a child depends on what happens at fertilisation.
Thus, father is responsible for the determination of the sex of a child.

Question: A blue colour flower plant denoted by BB is cross bred with that of white colour flower plant denoted by bb.
(a) State the colour of flower you would expect in their F₁ generation plants.
(b) What must be the percentage of white flower plants in F₂ generation if flowers of F₁ plants are self-pollinated?
(c) State the expected ratio of the genotypes BB and Bb in the F2 progeny.
Answer.

(i) The colour of all the flowers in F₁ generation will be blue
(ii) percentage of white flower plants in F₂ generation will be 25
(iii) The of genotype BB and Bb in F₂ progeny will 1 : 2

Question: What evidence do we have for the origin of life from inanimate matter?
Answer. Stanley L. Miller and Harold C. Urey provided evidence regarding origin of life from inanimate matter. They assembled an atmosphere similar to that existed on early earth. The atmosphere had molecules like ammonia, methane and hydrogen sulphide, but no oxygen and kept over water at temperature just below 100°C. Sparks were passed through the mixture of gases. At the end of a week, 15% carbon from methane had been converted to simple compounds of carbon like amino acids which make-up protein molecules. So, life arose afresh on earth.

Question: State the meaning of inherited traits and acquired traits. Which of the two is not passed on to the next generation? Explain with the help of an example.
Answer. Inherited traits are the characteristics transmitted from parents to their offspring.Acquired traits are characteristics which are developed during the lifetime of an individual.Acquired traits are not passed on to the next generation. For example, if we breed a group of mice, all their progeny will have tails. Now, if the tails of these mice are removed by surgery and allowed to breed, the next generation mice will also have tails. If these tails are also removed and allowed to breed, the progeny of mice will again have tails. Removal of tail by surgery is an acquired trait and do not change the genes of germ cells and hence, are not passed on to the next generation.

Question: What is meant by the term speciation? List four factors which could lead to speciation.
Answer. Speciation is the evolution of reproductive isolation among once interbreeding population.
Factors which can lead to speciation are:
Genetic drift: Over generations, genetic drift may accumulate which leads to speciation.
Natural selection: Natural selection may work differently in different location which may give rise to speciation.
Severe DNA change.
A variation may occur which does not allow sexual act between two groups.

Question: How do Mendel’s experiments show that the (a) traits may be dominant or recessive, (b) traits are inherited independently?
Answer. Mendel’s Experiments on Inheritance of Traits. Mendel used a number of visible contrasting characters of garden pea like round/wrinkled seeds, tall/short plants, white/violet flowers, etc.
Two Visible Contrasting Characters:
• Mendel took pea plants with two different characteristics such as plant with round and green seed and plant with wrinkled and yellow seeds and cross-pollinated then to get F₁ progeny.
• In F₁ progeny, all the plants will have round and yellow seeds. The round and yellow are dominant traits.
• Mendel then allowed F₁ progeny plants for self-pollination to get F₂ progeny.
• F₂ progeny will have plants with round and yellow seeds, round and green seeds, wrinkled and yellow seeds, wrinkled and green seed.
• The ratio of plants with above characteristics will be 9 : 3 : 3 : 1
• Therefore, round seed/wrinkled seed trait are independently inherited.
(a) In F1 progeny, all the plants will have round and yellow seeds. Wrinkled and green traits were not seen. But wrinkled and green characters appeared in the F2 progeny.
This means that wrinkle and green characters were recessive trait in F1 progeny, whereas round and yellow traits were dominant trait.
(b) New mixture of traits are seen in both F1 and F2 progeny. This means traits are independently inherited.

Question: “An individual cannot pass on to its progeny the experiences of its lifetime.” Justify the statement with the help of an example and also give reason for the same.
Answer. Experience achieved during the lifetime of an individual does not make any change in the gene of the individual.
For example, if a person reads a book on birds, the knowledge he earns by reading the book does not make any change in the gene, hence, this knowledge will not get automatically transmitted to his next generation. Such a trait is called acquired trait.

Question: What is the effect of DNA copying which is not perfectly accurate in the reproduction process?
Answer: DNA copying is imperative for reproduction and multiplication of species. When a cell or an organism is ready to reproduce asexually it makes a copy of its DNA which carries all the hereditary information in the form of genes. In most cases, DNA copying is accurate and progenies are exact copies of parents but very rarely error takes place
during this process and variations arise among the individuals of progeny. In sexually reproducing organisms, error in DNA copying accounts for variations during gametogenesis along with variation that always arise due to crossing over during meiotic divisions.

Question:All the variations in a species do not have equal chances of survival. Why?
Answer: All the variations do not have equal chances of survival in the environment in which they live. Depending on the nature of variations, different individuals would have different kinds of advantages. The organisms which are most adapted to the environment will survive.

Short Answer: 

Question. Explain how evolutionary relationship can be traced by the study of homologous organs.
Answer: Homologous organs provide morphological and anatomical evidences of evolution. There are number of organs in different groups of animals or plants which have similar basic design but are used for different purposes. These are termed as homologous organs. For example, the forelimbs of frog, lizard, bird and human beings show similarity in basic structure. The basic similarity of forelimbs of these different vertebrates indicates that all these have evolved from a common ancestor who had five digited or pentadactyle limbs which became modified according to the special needs of subsequent generations during the course of evolution. Hence, homologous organs depict divergent evolution or adaptive radiation.

Question. Why is variation beneficial for the species, but not necessarily for the individual?
Answer: Due to presence of variation, few individuals in population may survive under extreme conditions such as change in temperature, water level, etc.
Due to drastic change in niche, population except few individuals with variations can be wiped out.
This inbuilt tendency for variation is the basis of evolution and over time, such variations are useful for the survival of the species.

Question. How is the sex of the child fixed during the fertilisation step in human beings? Explain.
Answer: Human beings have 23 pairs chromosomes (22 pairs of autosomes +1 pair of sex chromosome). A male has one X chromosome and one Y chromosome whereas a female has two X chromosomes. Sex of a child depends on the two conditions which takes place during fertilisation.
The two conditions are given below:
(i) If a sperm carrying X chromosome fertilises an ovum which carries X chromosome, then the child born will be girl.
(ii) If a sperm carrying Y chromosome fertilises an ovum which carries X chromosome, then the child born will be a boy.

Question. “An individual cannot pass on to its progeny the experiences of its life-time”. Justify the statement with the help of an example and also give reason for the same. 
Answer: If we breed a group of mice, all the progeny of mice will have tails just like their parents. Now, if we remove the tails surgically and again breed them, we still get new mice with tails. This is because cutting the tails of mice does not change the genes of their reproductive cells (or gametes). And since the acquired trait of ‘cut tails’ does not bring about a change in the genes of mice, this trait cannot be passed on to their next generations. From this we conclude that the experiences acquired by an individual during his lifetime (called acquired traits) cannot be passed on to its progeny, and hence cannot lead to evolution because they are not caused by the change in genes.

Question. Describe any three ways in which individuals with a particular trait may increase in population.
Answer: Three ways in which individuals with a particular trait may increase in population are:
(i) Genetic drift : It is the random change in gene frequency occurring by chance fuuctuations.
In this phenomenon, an event may increase the frequency of a particular trait having little adaptive value and survival advantage.
(ii) Natural selection : It is the phenomenon wherein nature selects traits favourable to the species in the environment. Thus, a particular trait selected by the nature increases in number.
(iii) Geographical isolation : Interbreeding populations are geographically isolated by barriers such as mountain ranges, rivers and sea.
This geographical isolation leads to reproductive isolation and thus there is no gene flow between separated groups of population and therefore, population with particular character increases

Question. Why do mice whose tails were surgically removed just after birth for generations, continue to produce mice with tails?
Answer: A group of mice are normally bred and all their progeny possess tail. Now, if the tails of these mice are surgically removed in each generation, tail-less mice will not be produced. This is so because removal of tail during the life cycle of mice is an acquired character which is not transferred to future generations. The removal of the tail cannot change the genes of the germ cells of the mice.

Question. Give one example each of characters that are inherited and the ones that are acquired in humans. Mention the difference between the inherited and the acquired characters.
Answer: The difference between inherited and acquired characters is that the inherited character of an organism is caused by a change in its genes (or DNA) on the other hand acquired character of an organism is not inherited but develops in response to the environment. Eye colour is an example of inherited character whereas swimming is an example of acquired character in humans.

Question. “Only variations that confer an advantage to an individual organism will survive in a population.” Justify this statement.
Answer: Variations are the structural, functional or behavioural changes from the normal characters developed in the living organisms. Inheritable variations participate in evolution. According to Darwin, natural selection sorts out individuals with favourable variations. Such organism will survive, reproduce more and thus, will leave more progenies. Hence, useful variations get established in nature.

Question. Explain analogous organs and homologous organs. Identify the analogous and homologous organs amongst the following:
Wings of an insect, wings of a bat, forelimbs of frog, forelimbs of a human. 
Answer: The organs which are quite different in fundamental structure and embryonic origin but perform same function and may superficially look alike are called analogous organs The organs which perform different functions in different species but have similar basic structure and similar embryonic origin are called homologous organs.
Among the given examples: wings of an insect, wings of bat are examples of analogous organs whereas forelimbs of frog and human are examples of homologous organs.

Question: “We cannot pass on to our progeny the experience and qualifications earned during  our lifetime.” Justify the statement giving reason and examples.
Answer: Certain experiences and traits earned bypeople during their lifetime are not passed on to their next generations because all these characters are acquired by the man during his lifetime. The man is not born with these traits and he cannot pass on these traits to his children. These could be better explained by the given examples:
(i) Child of a very good swimmer may not know how to swim. This is so because the technique of swimming is not inherited from parents but it is learnt by the person himself or herself.
(ii) A person may have a scar on the face from a cut he got in an accident. This is also an example of acquired trait which cannot be passed to the next generation.
Traits can be passed on to future generations in which changes have occurred in the genes present in the reproductive cells of the parent organisms. These traits or characters are known as inherited traits.

Question: With the help of suitable examples, explain why certain traits cannot be passed on to the next generation. What are such traits called?
Answer: Certain experiences and traits earned bypeople during their lifetime are not passed on to their next generations because all these characters are acquired by the man during his lifetime. The man is not born with these traits and he cannot pass on these traits to his children. These could be better explained by the given examples:
(i) Child of a very good swimmer may not know how to swim. This is so because the technique of swimming is not inherited from parents but it is learnt by the person himself or herself.
(ii) A person may have a scar on the face from a cut he got in an accident. This is also an example of acquired trait which cannot be passed to the next generation.
Traits can be passed on to future generations in which changes have occurred in the genes present in the reproductive cells of the parent organisms. These traits or characters are known as inherited traits.

Question: What is meant by the term speciation? List four factors which could lead to speciation. 
Answer: The process by which new species develop from the existing species is known as speciation.
The four factors responsible for speciation are:
(i) Geographical isolation of a population leads to reproductive isolation and hence speciation.
(ii) Genetic drift leads of formation of new species by causing drastic changes in the frequencies of particular gene by chance alone..
(iii) Natural selection wherein nature in the wild selects traits favourable to the species in the given environment.
(iv) Random mating resulting in genetic variations in genotype frequencies within the population.

Question: List three main factors responsible for the speciation and briey describe each one of them.
Answer: Speciation is the process by which new species develop from the existing species.
The three important factors responsible for the speciation are :
(i) Geographical isolation of a population caused by various types of barriers such as mountain ranges, rivers and sea. Geographical isolation is the major factor in the speciation of sexually reproducing animals because it causes reproductive isolation and interrupts the flow of genes between their isolated populations through the gametes.
(ii) Genetic drift is the elimination of the genes of certain traits from the small population when a section of population dies of natural calamity or migrates to other region. It alters the gene frequency of the remaining population.
(iii) Variations introduced by random mating and hybridisation. Random fusion of gametes adds new alleles and it result in formation of new species.

Question: With the help of suitable examples explain natural selection.
Answer: Natural selection is the process by which organisms which are well adapted to the environment survive and reproduce and pass their successful characters to the next generation, while, organisms less adapted to the environment either fail to reproduce or die.
(i) When animals produce their progeny by sexual reproduction, some changes always appear in the progeny i.e., one of the progeny may be tall (having long legs) than the other one. When there is no food (grass, short plants, etc.) available on the ground, the progeny having long legs can easily reach the leaves on tall trees, eat them as food and survive. While the progeny having short legs cannot reach the leaves on tall trees, do not get any food, starve and hence die. Therefore, nature has selected the long-legged animals that will live enough to produce their offsprings. In course of evolution, the short legged animals evolved into long-legged animals due to favourable variations.
(ii) Birds evolved feathers as a means of providing insulation to their bodies in cold weather but later on these feathers became more useful for the purpose of flying. Hence, sometimes anevolutionary change produced in an organism for one purpose becomes more useful for an entirely different functions later.

Question: Explain with the help of an example each, how the following provide evidences in favour of evolution:
(a) Homologous organs
(b) Analogous organs
(c) Fossils
Answer: (a) Homologous organs perform different functions in different species but have similar basic structure and similar embryonic origin. For example forelimbs of a frog, lizard, bird and human being show similarity in basic structure. However, these organs perform entirely different functions but the basic similarity in the forelimbs of these different vertebrates indicates common ancestry.
This means that these vertebrates have modified according to the special needs of the subsequent generations during the course of evolution.
(b) Analogous organs are different in fundamental structure and embryonic origin but have similar appearance and perform similar functions. For example, the wings of an insect and a bird have different structures but they perform the same function of flying.The presence of these organs indicates that they are not derived from common ancestors but they can still evolve to perform similar functions to survive, flourish and keep on evolving in the prevailing environment. This provides a mechanism for evolution.
(c) Fossils are the remains or impressions of the dead animals and plants that lived in the remote past. The fossils provide evidence for evolution.
For example, a fossil bird called Archaeopteryx have characters of both reptiles and birds. It had feathers, fused bones and beak which are exclusive characters of birds and had teeth in the jaws, claws on fingers, a long tail, etc like reptiles. Thus, Archaeopteryx is a connecting link between the reptiles and birds, and hence suggests that the birds have evolved from the reptiles through the process of continuous evolution.

Question: One of the examples of two analogous organs can be wings of parrot and 
(a) Filler of whale (b) foreleg of horse
(c) Front leg of frog (d) wings of housefly
Answer: (d) wings of housefly Analogous organs are the organs which have same functions but their origin is different.
Accordingly, wings of parrot and wings of housefly have the same function of flying but their origin is different. The wings of parrot are mesodermal whereas housefly’s wings are ectodermal and supported by chitin.

Question: What will be the sex of a child who inherits Y chromosome from his/her father?
Answer: Male Explanation: a male has one X and one Y chromosomes which means half the male gametes i.e. sperms have X and the other half will have Y chromosome, whereas in females both the chromosomes are X thus all the females gametes will have one X chromosome. In humans the sex of the child depends on what happens at fertilization. If Y chromosome is inherited by the offspring then it will surely be a male because the child will have XY combination of sex chromosomes. 

Question: Name the scientific terms used to represent the following:
(a) The branch of biology which studies heredity and variation.
(b) The transmission of traits from parents to offspring.
(c) Differences in a trait in human beings.
(d) A recognisable feature of an organism.
Answer: (a) Genetics
(b) Hereditary
(c) Variation
(d) Character

Question: “Genes and chromosomes have similar behaviour.” Justify.
Answer: The following statement can be justified as:
•Chromosomes are thread like structure formed of DNA which carries genes which control characteristics of the offspring.
•Both genes and chromosomes carry hereditary information to the offspring.
•They both are an integral part of one another.
•Both occur in pairs.
•Both are found inside nucleus.

Question: Explain with an example how variation took place due to inheritance.
Answer: In sexual proliferation gametes experience meiosis which presents variation by crossing over, fertilization of gametes additionally presents variation. Offsprings hereditary material differs from the parents and along these lines legacy of qualities in sexual generation presents variation in species.

Long Answer:

Question. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O is dominant? Why?
Answer: In humans, genes for blood groups A and B are dominant over genes for blood group O but codominant to each other. Hence, genotype of man with blood group A will be either IAIA (homozygous dominant) or IAIO (heterozygous dominant). Genotype of woman with blood group O will be IOIO. The children of this couple will have the following probabilities for their blood groups :

Thus, gene for blood group A is dominant over gene for blood group O.

Question. How did Mendel’s experiments show that different traits are inherited independently? Explain.
Answer: In a dihybrid cross given by Mendel, it was observed that when two pairs of traits or characters were considered, each trait expressed independent of the other. Thus, Mendel was able to propose the Law of Independent Assortment which says about independent inheritance of traits. This could be explained clearly from the given cross:

F2 generation ratio : Round-yellow = 9, Roundgreen
= 3 Wrinkled-yellow = 3; Wrinkled-green =1

Question. How did Mendel explain that it is possible that a trait is inherited but not expressed in an organism?
Answer: Mendel first selected two pure line plants.
He then crossed such plants having contrasting characters. In the F1 generation, he observed that only one of the two contrasting character appeared, he called it dominant and the one which does not get expressed in F1 was recessive. He later selfed the F1 plants and observed that both the traits appear but in a de nite proportion. It can be explained by the following cross :

This is how Mendel explained that a trait may be inherited but not expressed in the plant.

Question. In one of his experiments with pea plants Mendel observed that when a pure tall pea plant is crossed with a pure dwarf pea plant, in the first generation, F1 only tall plants appear.
(a) What happens to the traits of the dwarf plants in this case?
(b) When the F1 generation plants were selffertilised, he observed that in the plants of second generation, F2 both tall plants and dwarf plants were present. Why it happened? Explain briefly.
Answer: (a) Mendel’s monohybrid cross indicated that out of two contrasting traits only one appears in the progeny of first generation. This implies that the trait which appears in F1 generation is dominant and the trait which does not express is recessive. We can also say that gene controlling the dominant trait is dominant gene or allele and gene controlling the recessive trait is recessive gene or allele.
In F1 progeny although the dominant trait is expressed but genes for both dominant and recessive traits are present in a heterozygous condition. The recessive trait has a chance to express in next generation only if recessive genes come in homozygous condition. This can be illustrated by the given cross:

(b) Appearance of suppressed recessive trait in individuals of F2 generation in Mendelian cross indicates that the characters of recessive traits are not lost even when they are not expressed. When the F1 generation plants were allowed to selffertilise, both the parental traits were expressed in definite proportion in F2 generation. This could be explained by the given cross by selfing the gametes obtained in F1 generation.

Question. How did Mendel interpret his result to show that traits may be dominant or recessive? Describe briefly. 
Answer: Mendel crossed the pea plant for two contrasting characters under consideration.
The trait that expressed itself in F1 generation was dominant and the one not expressed in F1 generation was recessive. He later selfed the plants of F1 generation and recovered, both parental traits in a definite proportion in F2 generation.
Mendel interpreted his results as, the trait that expressed itself in F1 was dominant and the one that reappeared in F2 generation was recessive. It can be demonstrated by the following cross :

Question. In a monohybrid cross between tall pea plants (TT) and short pea plants (tt) a scientist obtained only tall pea plants (Tt) in the F1 generation. However, on selfing the F1 generation pea plants, he obtained both tall and short plants in F2 generation. On the basis of above observations with other angiosperms also, can the scientist arrive at a law? If yes, explain the law. If not, give justification for your answer. 
Answer: In the situation discussed in the question the scientist can arrive at two different laws, i.e., law of dominance and law of segregation (or law of purity of gametes). This can be explained with the help of following crosses :

In F1 hybrid two dissimilar alleles are present for one character, i.e., height T is for tallness and t is for dwarfness, out of which only one allele called dominant allele expresses itself and the one which remains unexpressed is called recessive allele. This is called “law of dominance”.
Also the two dissimilar alleles that remain together in a heterozygous individual do not get mixed up and keep their distinct identity. Hence, at the time of gamete formation they separate so that each gamete receives only one allele and is always pure which enables reappearance of recessive trait in F2 progenies when the two recessive alleles come together. This is called “law of purity of gametes.”

Question. With the help of an example justify the following statement: “A trait may be inherited, but may not be expressed.”
Answer: A trait may be inherited but may not be expressed, this could be explained by the given example. When a tall pea plant was crossed with a dwarf pea plant, then F1 generation plants were all tall. When F1 plants were selfed, then F2 generation plants were both tall and dwarf. This shows that the F1 plants had inherited both the parental traits but did not express dwarfness or recessive trait in the presence of the trait for tallness or dominant trait. This could be explained by the given cross :

Question. List two differences in tabular form between dominant trait and recessive traits. What percentage/proportion of the plants in the F2 generation/progeny were round, in Mendel’s cross between round and wrinkled pea plants? 
Answer: Differences between dominant traits and recessive trait are given below:

Out of total 4 genotypes possible in F2 generation 31 genotypes result in phenotypic expression of round seeds. So, the percentage of plants with round seeds will be 75%. This can be illustrated as follows:

Question. Explain Mendel’s experiment with peas on inheritance of characters considering only one visible contrasting character.
Answer: Mendel crossed a pure tall pea plant with pure dwarf pea plant. All the plants obtained in F1 generation were tall. When Mendel selfed plants from F1 generation then he obtained both tall and dwarf plants in F2 generation in the ratio of 3 : 1. This can be illustrated as follows :

This explains that for each pair of contrasting characters there are two alleles. The trait which is expressed in F1 is dominant trait and is controlled by dominant allele and the trait which remains unexpressed in F1 is the recessive trait and is controlled by recessive gene. When both the contrasting alleles are present together in F1 individuals, no mixing of alleles occurs and they again segregate at the time of gamete formation Therefore, when the recessive alleles come together they result in reappearance of recessive trait in F2 generation.

Question. Define variation in relation to a species. Why is variation beneficial in the species?
Answer: The differences in the traits or characters shown by the individuals of a species are referred to as variations. Variations appear during reproduction whether organisms multiply asexually or sexually. Minor variations arise during asexual reproduction due to small inaccuracies in DNA copying. Sexual reproduction however, generates greater variations because of the following reasons:
(i) Chance separation of chromosomes during gamete formation (gametogenesis).
(ii) Crossing over during meiosis.
(iii) Chance coming together of chromosomes during fertilisation.
(iv) Mutations, i.e., alterations in the genetic material.
Some variations among individuals of a species
are favourable and helpful in better survival.
Depending upon the nature of variations, different individuals would have different kinds of advantages. For example, bacteria that can withstand heat will survive better in a heat wave
than others.

Question. A cross was made between pure breeding pea plants, one with round and green seeds and the other with wrinkled and yellow seeds.
(a) Write the phenotype of F1 progeny. Give reason for your answer.
(b) Write the different types of F2 progeny obtained along with their ratio when F1 progeny was selfed.
Answer: (a) The given cross was made between pure breeding pea plants, one with round and green seeds and the other with wrinkled and yellow seeds.
Yellow seed colour and round seed shape is dominant over green seed colour and wrinkled seed shape. In F1 generation, dominant traits express itself, whereas recessive traits get suppressed.

Therefore, the phenotype of F1 progeny is round and yellow.
(b) The different types of F2 progeny obtained along with their ratio when F1 progeny was selfed could be illustrated by the given cross:

Phenotypic ratio : 9 : 3 : 3 : 1
Round yellow seeds – 9 ; Round green seeds – 3
Wrinkled yellow seeds – 3 ; Wrinkled green seeds – 1

Question. (a) Mendel crossed tall pea plants with dwarf pea plants in his experiment. Write his observations giving reasons on the F1 and F2 generations.
(b) List any two contrasting characters other than height that Mendel used in his experiments in pea plants. 
Answer: (a) The possible cross of Mendel’s experiment is :

Hence, tall (T) is dominant whereas dwarf (t) is recessive. In F1 generation, only dominant trait expresses itself, whereas recessive trait gets suppressed.
In F2 generation, both traits, i.e., dominant and recessive express themselves . In this way, Mendel’s experiment showed that the traits (tall and dwarf) are inherited independently.
(b) The two contrasting characters other than height that Mendel used in his experiment in pea plants are round/wrinkled seeds and violet/white
flowers.

Question. A blue colour flower plant denoted by BB is cross-bred with that of white colour flower plant denoted by bb.
(a) State the colour of flower you would expect in their F1 generation plants.
(b) What must be the percentage of white flower plants in F2 generation if flowers of F1 plants are self-pollinated?
(c) State the expected ratio of the genotypes BB and Bb in the F2 progeny.
Answer: (a) The colour of the flower in F1 generation will be blue.
(b) If the flowers of F1 generations are self pollinated, then the percentage of white flowers in F2 generation must be 25%.
(c) The expected ratio of the genotypes BB and Bb in the F2 generation progeny is 1 : 2.
The above results could be depicted by the given cross:

Question. If we cross pure-breed tall (dominant) pea plant with pure-breed dwarf (recessive) pea plant we will get pea plants of F1 generation.
If we now self-cross the pea plant of F1 generation, then we obtain pea plants of F2 generation.
(a) What do the plants of F1 generation look like?
(b) State the ratio of tall plants to dwarf plants in F2 generation.
(c) State the type of plants not found in F1 generation but appeared in F2 generation, mentioning the reason for the same.
Answer: (a) The plants of F1 generation will be all tall plants.
(b) The ratio of tall plants to dwarf plants in F2 generation is 3 : 1.
(c) Dwarf plants are not found in F1 generation but appeared in F2 generation. This is so because in F1 generation only dominant trait (tall) expresses itself and recessive trait (dwarf) gets suppressed.
The dwarf plants appeared in F2 generation, because the traits whether dominant or recessive are independently inherited. In others words, a single copy of (T) is enough to make the plant tall, while both copies have to be (t) for the plant to be dwarf.

Question. Write a difference between inherited traits and acquired traits giving one example of each.
Answer: A trait (or characteristic) of an organism which is ‘not inherited’ but develops in response to the environment is called an acquired trait. For example, if a group of mice are normally bred, all their progeny will have tails. Now, if the tails of these mice are cut by surgery in each generation, tail-less mice will not be produced. This is so because removal of tail is an acquired character. A trait (or characteristic) of an organism which is caused by a change in its genes (or DNA) is called an inherited trait . Inherited traits can be passed on to the progeny of the organism because they have produced changes in the genes (or DNA) of the organism. For example, skin colour in human beings.

Question. (a) Why did Mendel choose garden pea for his experiments ? Write two reasons.
(b) List two contrasting visible characters of garden pea Mendel used for his experiment.
Answer: (a) Mendel chose garden pea for his experiments because:
(i) It was easy to grow and it shows some clear contrasting traits like some pea plants are tall whereas others are dwarf.
(ii) Pea plants are self pollinating and many generation of pea plants can be produced in comparatively less time.
(b) The contrasting characters of garden pea plant studied by Mendel are:

Question. With the help of two suitable examples, explain why certain experiences and traits earned by people during their lifetime are not passed on to their next generations. When can such traits be passed on? 
Answer: Certain experiences and traits earned by people during their lifetime are not passed on to their next generations because all these characters are acquired by the man during his lifetime. The man is not born with these traits and he cannot pass on these traits to his children. These could be better explained by the given examples:
(i) Child of a very good swimmer may not know how to swim. This is so because the technique of swimming is not inherited from parents but it is learnt by the person himself or herself.
(ii) A person may have a scar on the face from a cut he got in an accident. This is also an example of acquired trait which cannot be passed to the next generation.
Traits can be passed on to future generations in which changes have occurred in the genes present in the reproductive cells of the parent organisms.
These traits or characters are known as inherited traits.

Question. What is speciation? Explain in brief the role of natural selection and genetic drift in this process. 
Answer: The process by which new species develop from the existing species is known as speciation.
Both natural selection and genetic drift play a very important role in speciation. By natural selection traits favourable to the species in the given environment are selected by the nature.
Example, beetles develop colur variation during reproduction. Consequently, in the progeny, one beetle develops green body colour instead of normal red colour. This beetle can inherit this variation in colour on to its progeny so that all its offispring are green in colour. Crows cannot easily locate green-coloured beetles on the green leaves of bushes and continue to eat red beetles which are easily located on green leaves. As a result, in population of green beetles increases in each generation.
Genetic drift is the elimination of the genes of certain traits from the small population when a section of population dies of natural calamity or migrates to other region. It alters the gene frequency of the remaining population.
Suppose in sexually reproducing red beetle population, a colour variation arises wherein one beetle develops blue body colour instead of red.
This beetle can also pass this colour variation to its progeny so that all its offisprings are blue coloured beetles. As the population of beetles expand, initially there would be few blue coloured beetles among the majority of red coloured beetles. At this point, an elephant comes by and stamps on the bushes where the beetles live. Consequently, most of the beetles get killed. By chance, most of the survived beetles are of blue colour. This population again slowly multiply and will contain mostly blue coloured beetles over a period of time. Survival of more blue beetles in the population changed the coloured characteristic from normal red to blue over a period of time. In small population, accidents can change the frequency of some genes in a population, even if it does not give any survival advantage to the possessors.

Question. What is speciation? List four factors responsible for speciation. 
Answer: The process by which new species develop from the existing species is known as speciation.
The four factors responsible for speciation are:
(i) Geographical isolation of a population leads to reproductive isolation and hence speciation.
(ii) Genetic drift leads of formation of new species by causing drastic changes in the frequencies of particular gene by chance alone..
(iii) Natural selection wherein nature in the wild selects traits favourable to the species in the given environment.
(iv) Random mating resulting in genetic variations in genotype frequencies within the population.

Question. “It is a matter of chance whether a couple will have a male or a female child.” Justify this statement by drawing a flow chart.
Answer: Sex is determined at the time of fertilisation when male and female gametes fuse. Male produces two types of gametes, i.e., having X or Y chromosome and female produces same type of gametes containing X chromosomes. The sex of the child is determined at the time of fertilisation when male and female gametes fuse to form zygote.
If a sperm (male gamete) carrying X chromosome fertilises an egg or ovum (female gamete) carrying X chromosome, then the offispring will be a girl (female). This is because the offispring will have XX combination of sex chromosomes.
If a sperm (male gamete) carrying Y chromosome fertilises an egg or ovum (female gamete) which has X chromosome, then the offispring will be a boy (male). This is because the offispring will have XY combination of sex chromosomes.
Therefore, there are 50% chance of a male child and 50% chance of a female child.

Question. List three main factors responsible for the speciation and briefly describe each one of them. 
Answer: Speciation is the process by which new species develop from the existing species.
The three important factors responsible for the speciation are :
(i) Geographical isolation of a population caused by various types of barriers such as mountain ranges, rivers and sea. Geographical isolation is the major factor in the speciation of sexually reproducing animals because it causes reproductive isolation and interrupts the flow of genes between their isolated populations through the gametes.
(ii) Genetic drift is the elimination of the genes of certain traits from the small population when a section of population dies of natural calamity or migrates to other region. It alters the gene frequency of the remaining population.
(iii) Variations introduced by random mating and hybridisation. Random fusion of gametes adds new alleles and it result in formation of new species.

Question. With the help of suitable examples explain natural selection.
Answer: Natural selection is the process by which organisms which are well adapted to the environment survive and reproduce and pass their successful characters to the next generation, while, organisms less adapted to the environment either fail to reproduce or die.
(i) When animals produce their progeny by sexual reproduction, some changes always appear in the progeny i.e., one of the progeny may be tall (having long legs) than the other one. When there is no food (grass, short plants, etc.) available on the ground, the progeny having long legs can easily reach the leaves on tall trees, eat them as food and survive. While the progeny having short legs cannot reach the leaves on tall trees, do not get any food, starve and hence die. Therefore, nature has selected the long-legged animals that will live enough to produce their offisprings. In course of evolution, the short legged animals evolved into long-legged animals due to favourable variations.
(ii) Birds evolved feathers as a means of providing insulation to their bodies in cold weather but later on these feathers became more useful for the purpose of flying. Hence, sometimes an evolutionary change produced in an organism for one purpose becomes more useful for an entirely different functions later.

Question. Distinguish between homologous organs and analogous organs. In which category would you place wings of a bird and wings of a bat? Justify your answer giving a suitable reason.
Answer: Those organs which have the same basic structure and similar embryonic origin but different functions are called as homologous organs. These organs follow same basic plant of organisation during development, but in adults got modified to perform different function as an adaptation to different environments. Those organs which have different basic structure and embryonic origin but perform similar functions are called analogous organs. The wings of bird and wings of bat are analogous organs because the basic structure or design of the wings of bird and bat are different but they perform the similar function of flying. 

Question. Define the term “evolution”. Evolution should not be equated with progress.” Give reason to justify this statement.
Answer: Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years in which new species are produced.
Evolution should not be equated with progress because there is no real progress in the concept of evolution. Evolution is just the production of diversity of life forms and shaping of this diversity by the environmental selection. The only progress in evolution appears to be that more and more complex body designs of organisms have emerged over the ages. This will become clear from the following examples. When a new species is formed, it is not necessary that the old species will disappear or get eliminated from earth. It will all depend on the environment. Also it is not as if the newly formed species are in any way better than the older ones. It is simply that genetic drift and natural selection processes have combined to form a population having different body design which cannot interbreed with the older population.
It is a common belief that chimpanzees are the ancestors of human beings. It is, however, not true that human beings have evolved from chimpanzees. Actually, both chimpanzees and human beings had a common ancestor long time ago. The two offisprings of that ancestor evolved in their own separated ways to form the modern day chimpanzees and human beings.

Question. What are fossils? What do they tell about the process of evolution?
Answer: Fossils are the remains or impressions of the dead animals and plants that lived in the remote past. The fossils provide evidence for evolution.
For example, a fossil bird called Archaeopteryx have characters of both reptiles and birds. It had feathers, fused bones and beak which are exclusive characters of birds and had teeth in the jaws, claws on fingers, a long tail, etc like reptiles. Thus, Archaeopteryx is a connecting link between the reptiles and birds, and hence suggests that the birds have evolved from the reptiles through the process of continuous evolution.

Question. Explain with the help of an example each, how the following provide evidences in favour of evolution:
(a) Homologous organs
(b) Analogous organs
Answer: (a) Homologous organs perform different functions in different species but have similar basic structure and similar embryonic origin. For example forelimbs of a frog, lizard, bird and human being show similarity in basic structure. However, these organs perform entirely different functions but the basic similarity in the forelimbs of these different vertebrates indicates common ancestry.
This means that these vertebrates have modified according to the special needs of the subsequent generations during the course of evolution.
(b) Analogous organs are different in fundamental structure and embryonic origin but have similar appearance and perform similar functions. For example, the wings of an insect and a bird have different structures but they perform the same function of flying. The presence of these organs indicates that they are not derived from common ancestors but they can still evolve to perform similar functions to survive, flourish and keep on evolving in the prevailing environment. This provides a mechanism for evolution.

Question. “Evolution and classification of organisms are interlinked”. Give reasons to justify this statement. 
Answer: Evolution is the process by which newer types of organisms are developed from the pre-existing ones through modifications. Classification is the arrangement of organisms into a series of groups based on physiological, biological, anatomical or other relationships. All systems of classification are hierarchial. The more closely two species are related, the more recently they have a common ancestor. Classification of organisms necessarily involves organising them in different groups, based on the similarities and differences of characteristics. It helps in the recognisation of the basic arrangement of a hierarchical structure among diverse species. It facilitates studies or research of wide variety associated with organisms effortlessly. Thus, classification of species is infact a refection of their evolutionary relationship or we can say that evolution and classification are interlinked.

Question. How do Mendel’s experiments show that (a) traits may be dominant or recessive?
(b) inheritance of two traits is independent of each other? 
Answer: (a) Mendel first crossed pure-bred tall pea plants with pure-bred dwarf pea plants and found that only tall pea plants were produced in the first generation (F1). He then self crossed the tall pea plants of the F1 generation and found that tall plants and dwarf plants were obtained in the second generation or (F2) in the ratio of 3:1. Mendel said that the trait of dwarfness of one of the parent pea plant had not been lost, it was merely concealed or suppressed in the first generation to re-emerge in the second generation. He called the suppressed trait of ‘dwarfness’ as ‘recessive trait’ and the expressed trait of ‘tallness’ as the ‘dominant trait’.
In this way, Mendel’s experiments with tall and dwarf pea plants showed that the traits may be dominant or recessive.
Hence this could be explained by the given cross :

(b) Mendel observed that he had started with two combinations of characteristics in seeds, round-yellow and wrinkled -green, and two new combinations of characteristics had appeared in the F2 generation, round-green and wrinkled-yellow.
According to Mendel’s second law of inheritance more than one pair of traits are considered in a cross simultaneously, the factors responsible for each pair of trait are distributed independently to the gametes.
The cross given below showing dihybrid cross explains that the inheritance of two traits is independent of each other.

F2 generation : Round-yellow = 9, Round-green = 3
Wrinkled-yellow = 3; Wrinkled-green =1

Question. Explain the following:
(a) Speciation
(b) Natural selection. 
Answer: (a) Speciation : Origin of new species from existing one due to reproductive isolation of a part of its population is called speciation.
Suppose a large population of beetle living in an area gets split into two sub populations due to geographical barriers like river, mountain, sea, etc. Then members of these sub-populations will not be able to interbreed. Hence, there will be no gene flow between the members of these populations. After few generations, genetic drift will accumulate different variations in each of the two geographically separated sub-populations.
Natural selection may also operate simultaneously in a different way in these geographically isolated sub-populations. This makes geographically isolated sub-populations to become more and more different from each other and ultimately reproductive isolation occurs between individuals of these groups and they transform into new species.
(b) Natural selection is the phenomenon wherein nature, in the wild, selects traits favourable to the species in its environment.

Question. How are fossils formed? Describe, in brief, two methods of determining the age of fossils.
Answer: When organisms like plants or animals die, their bodies get decomposed by the action of microorganisms in the presence of oxygen, moisture, etc. Sometimes the conditions in the environment are such (like absence of oxygen, moisture, etc.), which do not let the body of the organism to get decompose completely. It is the body (or body part) of an organism which we get as fossil on digging the earth. In many cases the soft parts of the organisms get decomposed and we get skeleton of hard parts (like teeth, bones, etc.) as fossil. Even the soft parts of the plants and animals (which usually decompose quickly) are sometimes preserved as fossils in the form of their impressions inside the rocks. For example, if a dead leaf gets caught in mud, it will not decompose quickly. The mud around the leaf will set around it as a mould, gradually harden to form a rock and retain the impression of the leaf. This forms a leaf fossil which can be dug out from the earth a after a long time period.
The age of fossils can be determined in two ways as given below :
(i) By the relative method : When we dig into the earth, we find fossils at different depths. The fossils which we find in layers closer to the surface of the earth are more recent and those fossils which are found in deeper layers are older; whereas the fossils found in the deepest layers of earth are the oldest ones.
(ii) Carbon dating method : When a living object dies and forms fossil, its carbon-14 radioactivity goes on decreasing gradually. By this method, the age of fossils is found by comparing the carbon-14 radioactivity left in fossils with the carbon-14 radioactivity present in living objects today.

Question. What are fossils? Describe the importance of fossils in deciding evolutionary relationship between organisms.
Answer: Fossils are the remains or impressions of the dead animals and plants that lived in the remote past. Fossils occur in sedimentary rocks, peat, amber, asphalt, lava and snow. These provide direct evidence of evolution. Fossils play a very important role in establishing evolutionary relationship between organisms. The age of fossils can be approximately assumed through varioustechniques which gives an idea of the time period in the geological time scale when a particular organism existed. Some of the morphological features of organisms are well preserved which give a clue about their ancestors and descendants.

Question. Define evolution. How does it occur?
Describe how fossils provide us evidences in support of evolution. 
Answer: Evolution is the sequence of gradual changes, from simple life forms to complex life form, i.e., from primitive organisms that lived over millions of years ago to new organisms that exist today.
Evolution occurs by changes, improvement and modification of simple life forms. Fossils are the remains or impressions of organisms that lived in the remote past. Fossils provide the evidence that the present animal have originated from previously existing ones through the process of continuous evolution. Fossils can be used to reconstruct evolutionary history of an organism.
The distribution pattern of fossils shows that the ancient fossils present in the bottom rocks are simple, while the most recent fossils found in the upper strata are more highly evolved. It means fossils form and become more and more complex as we proceed from earliest to recent rocks. It gives us an idea of time in history when different species were formed or became extinct. Thus, fossils provide us evidences in support of evolution.

Question. (a) Planaria, insects, octopus and vertebrates all have eyes. Can we group eyes of these animals together to establish a common evolutionary origin? Justify your answer.
(b) “Birds have evolved from reptiles”. State evidence to prove the statement.
Answer: (a) Planaria, insects, octopus and vertebrates cannot be grouped together on the basis of eye.
Eyes of insects, octopus, Planaria and vertebrates are analogous organs which have developed over generation as an adaptation for similar function. They represent convergent evolution where distantly related groups develop similar functional structure as an adaptation for same function.
(b) Fossil bird Archaeopteryx had features like feathers, fused bones, beak which are the characteristic features of birds. It also had some features of reptiles, like, teeth in jaws, claws on free fingers, a long tail, etc. Thus, it represents a connecting link between reptiles and birds. This example provides a clue that birds have evolved from reptiles.

Question: Explain with an example how traits get expressed.
Answer: Hereditary information which must be carried on to offsprings is stuffed in the core of the cell i.e. nucleus. It contains the hereditary material of the cell as chromosomes. A chromosome is a structure of DNA and protein found in cells.
Chromosome is a solitary bit of coiled DNA containing genes. Chromosomes are thought to be the vehicles of heredity as they convey genes. Genes control
characteristics. Proteins formed from RNA are in charge of the traits. These traits can be expressed as phenotype {appearance} or genotypes {genetic make-up}. 

The central dogma of life.

Question:. How does DNA help in defining evolutionary relationship?
Answer: All life forms have contained DNA and use the same four nitrogenous basesadenine, thymine, cytosine and guanine in their genetic code to synthesize proteins.
DNA helps in defining the evolutionary relationship “utilizing a sequence of DNA “the connection between the living beings is dictated by their DNA sequence. The arrangement of the nucleotides in DNA of the life forms are particular and are controlled by the researcher who utilizes this data and looks at the arrangement and discovers the similitudes in this manner helping in the characterizing the advancement relationship of living beings. These data likewise used to characterizes the distinction between organisms. Researcher likewise utilized the sequence to find it.

Question: Explain Mendel’s experiment with peas on inheritance of traits considering two visible contrasting characters.
Answer: Mendel crossed a pea plant that was homozygous and prevailing for round (RR), yellow (YY) seeds with a pea plant that was homozygous and latent for wrinkled (rr), green (yy) seeds, spoke to by the accompanying documentation:
RRYY x rryy 

Living beings in this underlying cross are known as the parental, or P age. The offsprings of the RRYY x rryy cross, which is known as the F1 age, were all heterozygous plants with round, yellow seeds and the genotype RrYy.
Next, Mendel crossed two plants from the F1 age. This progression is the dihybrid cross, and it is spoken to as:
RrYy xRrYy Mendel observed that the F2 descendants of his dihybrid cross had a 9:3:3:1 proportion and created nine plants with round, yellow seeds, three plants with round, green seeds, three plants with wrinkled, yellow seeds and one plant with wrinkled, green seeds. From his analysis, Mendel watched that the sets of attributes in the parental age arranged autonomously from each other, starting with one age then onto the next.

Dihybrid cross

Question: ‘Non-living material must have given rise to life’. Describe with an example.
Answer: This can be demonstrated with help of Miller and Urey experiment:
They took a blend of alkali, hydrogen sulphide and methane and water and gave it a temperature of just underneath 100 degree Celsius and presented it to 25000 V electric sparkles to take after the lightning. Following 8-10 days 15% of carbon from methane had been changed over into organic compounds such as carbohydrates, proteins, fatty acids etc. which could react to form complex compounds. So fundamentally life originated from lifeless issue. 

Question: What role does sexual reproduction play in evolution?
Answer: In sexual proliferation gametes experience meiosis which presents variation by crossing over, fertilization of gametes additionally presents variation. Offsprings hereditary material differs from the parents and along these lines legacy of qualities in sexual generation presents variation in species.

Question: While playing near a sugarcane field, Mohan noticed that the plants are almost similar to one another. At the same time, he noticed the mango trees in
the next plot of land which are not similar to one another. Mohan’s brother told Mohan that sugarcane reproduces asexually, hence there is little variation, Mango reproduces sexually, and hence there is larger variation.
(a) Why sugarcane cannot reproduce sexually?
(b) Can mango reproduce asexually?
(c)If a person wants to have a flower garden, what type of plants should he grow?
Answer: (a) flowers are absent in sugarcane which implies lack of pollen grains and anthers thus lacking sexual reproduction.
(b) Yes by means of grafting or layering.
(c) If a person wants to have a flower garden then he should grow plants obtained from vegetative propagation.

Question: On the basis of the possibilities of combination of the sex chromosomes, what percentage probability does a couple have of having a son or a daughter?
Show the same by making a cross.
Answer: A male has one X and one Y chromosomes which means half the male gametes i.e. sperms have X and the other half will have Y chromosome, whereas in females both the chromosomes are X thus all the females gametes will have one X chromosome. In humans the sex of the child depends on what happens at fertilization. If Y chromosome is inherited by the offspring from male then it will surely be a male because the child will have XY combination of sex chromosomes. If X from both the parents then the offspring will be a female having XX combination. 

Possibilities for the sex of offspring.

Question: Explain with example how characteristics of a population changes over the
years for the following situations-
(a) To gain survival advantage
(b) Due to accidental survival
(c) Temporary change of characteristics.
Answer: Characteristics of a population changes over the years for their survival in nature. This can be justified with these examples:
(a) To gain survival advantage: the best example is provided by the peppered moth in order to survive these moths then changed their colour to grey and now blended perfectly with soot coated trees.
(b) Due to accidental survival: Beetles are of two colour either red or blue. It was seen that elephants crushed all the red coloured beetle but not blue hence this example shows accidental survival.
(c) Temporary change of characteristics: Speciation of any plant or animal to the modern one is an example of temporary change of characteristics so as to bring about a finally best-suited species.