Exam Question for Class 10 Science Chapter 9 Heredity And Evolution
Please refer to below Exam Question for Class 10 Science Chapter 9 Heredity And Evolution. These questions and answers have been prepared by expert Class 10 Science teachers based on the latest NCERT Book for Class 10 Science and examination guidelines issued by CBSE, NCERT, and KVS. We have provided Class 10 Science exam questions for all chapters in your textbooks. You will be able to easily learn problems and solutions which are expected to come in the upcoming class tests and exams for standard 10th.
Chapter 9 Heredity And Evolution Class 10 Science Exam Question
All questions and answers provided below for Exam Question Class 10 Science Chapter 9 Heredity And Evolution are very important and should be revised daily.
Exam Question Class 10 Science Chapter 9 Heredity And Evolution
Very Short Answer Type Questions:
Question: Do all variations in a species have equal chances of surviving in the environment in
which they find themselves?
Answer: No, all variations in a species do not have equal chances of surviving in the environment in which they find themselves. Depending upon the nature of variations, each individual would have different advantages of survival.
Question: In a study it was found that fused ear lobes were found in more numbers within a population rather than free ear lobes. What
can you infer from the above observation with respect to dominant / recessive trait?
Answer: It can be inferred from the observation that fused ear lobes were found in more numbers within a population that fused ear lobes is a dominant trait whereas free ear lobes is a recessive trait.
Question: The gene type of green stemmed tomato plants is denoted as GG and that of purple stemmed tomato plants as gg. What colour of stem would you expect in F1 progeny when these two are crossed?
Answer: As green stem is a dominant trait as compared to purple stem, the colour of stem would be green in F1 progeny.
Question: Mendel took tall pea plants and short pea plants and produced F1 progeny through
cross-fertilisation. What did Mendel observe in the F1 progeny?
Answer: When Mendel cross fertilized tall pea plants and short pea plants, he observed that all plants in the F1 progeny were tall.
Question: Mendel crossed the round and green seeded pea plants with the wrinkled and yellow seeded pea plants. Give the phenotypic ratio of F2 generation.
Answer: The phenotypic ratio of F2 generation when round and green seeded pea plants were crossed with the wrinkled and yellow seeded pea plants is: Round Yellow : Round Green :
Wrinkled Yellow : wrinkled Green = 9: 3 : 3 : 1.
Question: Are there any organisms where sex of the newborn is not genetically determined? Give example.
Answer: Yes, there are organisms in which sex of the newborn is not genetically determined. An example is snail, which can change its sex.
Question: How is the normal number of chromosomes restored in the progeny of sexually reproducing organisms?
Answer: Each cell has two copies of each chromosome, one each from the male and female parents. Each germ cell or gamete takes one chro mosome from each pair and when two germ cells combine, the original number of chromosomes is restored in the progeny.
Question: If a pure tall pea plant is crossed with a pure dwarf pea plant, then in F1 generation only tall plants appear. What happens to the traits of the dwarf plant?
Answer: Although in F1 generation only the tall plants appear, both the tallness and dwarfness traits are inherited in the F1 plants but as the tallness trait is dominant, it is expressed, whereas, dwarfness trait being recessive is not expressed.
It is expressed in F2 generation.
Question: Give reason: Phenotypic and genotypic ratiosare different.
Answer: The phenotypic ratio in F2 generation when F1 tall plants are crossed with each other is Tall : Dwarf = 3 : 1
Whereas, the genotype ratio will be TT : Tt : tt = 1 : 2 : 1 .
Here, both TT and Tt refer to tall plants, they have
the same phenotype but different genotype.
Short Answer Type Questions:
Question: (A) Why is the F1 progeny always of tall plants when a tall pea plant is crossed with a short pea plant?
(B) How is F2 progeny obtained by self- pollination of F1 progeny different from F1 progeny? Give reason for this observation.
(C) State a conclusion that can be drawn on the basis of this observation.
Answer: (A) F2 progeny always show the traits of only one of the parent plants.
(B) F1 progeny obtained by self pollination of F1 progeny is different from F1 progeny because both the parental traits are expressed in definite proportion in F2 generation.
(C) There are a pair of factors for each character eq. Tallness (TT). When gametes are formed these factors segregate and each gamete receives only one factor of each character. This is called Law of segregation.
(1) In F1 generation only one character was expressed which Mendel called it as dominant character (tallness) and the other which does not express itself was termed recessive (dwarfness). The appearance of only one of the two contrasting traits in F1 generation is termed as Law of dominance. All plants
produced in F1 progeny are all tall (Heterozygous TT).
(2) When two Tt (hybrid) plants are self pollinated, F2 progeny shows three tall and one dwarf.
(3) Genotypic ratio in F2 generation is TT : Tt : tt
Question: Why do all the gametes formed in human females have an X chromosome?
Answer: Women have a perfect pair of sex chromosomes, both called X. Women are XX, while men are XY.
All children will inherit an X chromosome from their mother regardless of whether they are boys or girls. Thus, the sex of the children will be determined by what they inherit from their father. A child who inherits an X chromosome from her father will be a girl. During meiosis, one X chromosome enters each gamete. Hence, all the gametes formed in human females have an X chromosome.
Question: (A) Why did Mendel carry out an experiment to study inheritance of two traits in garden-pea?
(B) What were his findings with respect to inheritance of traits in F1 and F2 generation?
(C) State the ratio obtained in the F2 generation in the above mentioned experiment.
Answer: (A) Mendel carried out an experiment to study inheritance of two traits in garden pea to see the interaction and basis of inheritance between them. He also concluded that also traits segregate during gamete formation and finally he gave three laws.
(1) Law of segregation
(2) Law of Dominance
(3) Law of Independent Assortment
(B) Mendel observed that—In F1 generation, feature of only one parental type appear.
The features of other parents were not expressed. He called the first one which appeared as dominant features/ character and the other features which did not appear called them as recessive.
The characters are not lost even when they are not expressed.
When F1 off springs were allowed to be self pollinated, both the parental traits were expressed in definite proportion in F2 generation.
He had started with two combinations of characteristics and two new combinations of characteristics and appeared in F2 generation.
From the F2 generation of a dihybrid cross Mendel postulated that inheritance of factors which control a particular trait in an organism are independent of the other. Thisis called law of Independent Assortment.
(C) Ratio obtained in the F2 generation in the above mentioned experiment
9 : 3 : 3 : 1
Explanation: r = Round
w = wrinkled
y = yellow
g = green
Question: Does the occurrence of diversity of animals on Earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Answer: The diversity of animals on Earth does not suggest their diverse ancestry. At present, there is a huge diversity of animals on Earth. But we can group the animals into different groups and subgroups on the basis of certain common characters. Having a single ancestor would limit the diversity seen in the organisms today.
For example all birds are closely related, they have common ancestors, but birds and bat are also related because they have analogous organ, i.e. their wings. Thus, it can be said that the occurrence of animals on earth explains their diverse ancestry.
Diverse habitat of these groups caused them to develop different characters and to look diverse from each other thus sharing the occurrence of diversity of animals and their ancestry them today. Thus, a common ancestry for all the animals is not a likely theory.
Question: In a pea plant, the trait of flowers bearing purple colour (PP) is dominant over white colour (pp). Explain the inheritance pattern of F1 and F2 generations with the help of a cross following the rules of inheritance of traits. State the visible characters of F1 and F2 progenies.
Visible characters of F1 progeny all flowers are purple coloured and in F2 progenies 3 are purple coloured and 1 is white coloured flower.
Question: Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive:
(A) Yellow seed
(B) Round seed
Question: Newly formed DNA copies may not be identical at times. Give reason.
Answer: The replication of DNA in the cell is done by biochemical reactions. No biochemical reaction can reproduce exactly the same result. So, when the DNA present in the nucleus of the parent cell undergoes replication, then slight variations occur in the two DNA copies formed.
Due to this, the two DNA molecules formed will be similar but may not be exactly identical to the parent DNA.
These variations in the replication of DNA molecule will also lead to slight variations in the offspring produced by asexual reproduction.
Question: A woman has only daughters. Analyze the situation genetically and provide a suitable explanation.
Answer: Women have a perfect pair of sex chromo- somes, both called X. But men have a mis- matched pair, in which one is a normal-sized X, while the other is a short one called Y. So, women are XX, while men are XY. All children will inherit an X chromosome from their mother.
A child who inherits an X chromosome from her father will be a girl and the one who inherits a Y chromosome from him will be a boy. It is given that the woman has only daughters.
This indicates that in every fusion, the sperm carrying the X chromosome fertilized the ovum.
Question: What is the phenotypic ratio obtained in Mendels dihybrid cross?
Answer: The phenotypic ratio obtained in Mendel’s dihybrid cross is 9:3:3:1.
Phenotypic ratio is the way in which the samples appear physically.
For example, in a dihybrid cross, Mendel took round-yellow seeds and wrinkled-green seeds as samples.
After the dihybrid cross, the following traits were appeared in the ratio 9:3:3:1
(1) Round-yellow seeds : 9
(2) Round-green seeds : 3
(3) Wrinkled-yellow seeds : 3
(4) Wrinkled-green seeds : 1
Question: A red haired woman marries a brown haired man, and all the children are brown haired.
Explain this genetically.
Answer: A red haired woman marries a brown haired man, and all the children are brown haired. The brown hair colour genes are dominant to the red hair colour genes.
A brown haired man can have BB factors or Bb as only one dominant factor expresses itself in the next generation.
(1) In situation 1 brown hair man bas a pure strain i.e. BB and all the children an brown haired.
(2) In situation 2 brown hair man carriers recessive red coloured hair trait gametes
formed fertilize and results into 50% brown and 50% red haired children. So in the given situation, brown haired man has passed the pure factors i.e., BB because all the children are brown haired.
That is why the children were having brown coloured hairs.
Question: (A) Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
(B) Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer: (A) The geographical isolation will not be a major factor in the speciation of a self- pollinating plant species. The reason behind this is that these species will not have to depend on other plants for process of reproduction to be carried out.
(B) Geographical isolation also cannot be a major factor in the speciation of an asexually reproducing organism because it does not require any other organism to carry out the process of reproduction.
Question: What are Mendel’s laws of inheritance?
Answer: Mendel’s Laws of inheritance are:
(1) Law of dominance: When two homozygous individuals with one or more sets of
contrasting characters are crossed the characters that appear in the F1 hybrids are
(2) Law of segregation: The characteristics of an organism are determined by internal factors which occur in pairs. Only one of a pair of such factors can be present in a single gamete.
(3) Law of independent assortment: In the inheritance of more than one pair of contrasting characters in a cross simultaneously, the factors responsible
for each pair of traits are distributed independently to the gametes.
Explanation: Law of segregation and law of dominance can be explained by monohybrid cross. When Mendel crossed pure-breed tall pea plants (TT) with pure breed dwarf plants (tt), he found only tall plants were produced in F1 generation and concluded that in F1 generation, traits of only parent plant i.e., tall expresses itself.
Then he crossed (Tt) plants of F1 generation and found that tall and dwarf plants of F1 generation and found that tall and dwarf plants are present in F1 generation in the ratio of 3 : 1.
Mendel noted the dwarfness traits which disappeared in F1 generation, reappeared in F2 generation. Mendel called the dwarfness trait as recessine trait and tallness trait as domant trait. This proves law of dominance.
In F1 and F2 generation, Mendel noted only one of a pair of factors was present in a single gamete. So this process that the factors get segretated and law of segretation.
Law of independent assortment can be explained by Dihybrid cross. Mendel first crossed pea plants having pure breed and yellow seeds with pure having breed wrinkled-green seeds. He obtained plants having only round-yellow seeds. But when crossed these plants, he obtained plants having different characteristics in F2 generation.
Round yellow seed: 9
Round green seed: 3
Wrinkled yellow seed: 3
Wrinkled green seeds: 1
Mendel observed that he had started with two contrasting pair of characteristics in seeds: round yellow and wrinkled-green and two new combinations of characteristics had appeared in F2 generation: round-green and wrinkled yellow. He concluded though the two pairs of original characteristics combine in F1 generation but they separate and behave independently in subsequent generations.
Question: A group of grass hoppers – some green and some brown-lived in grassland having dry bushes and dry grass.
(A) Which one would normally be picked up by predatory birds and why?
(B) Population of which grasshopper will increase?
(C) Name this phenomenon.
Answer: (A) Green grasshoppers would be normally picked up by predatory birds because they can be easily seen in dry bushes and grasses as compared to brown grasshoppers.
(B) As brown grasshoppers would be eatenless, their population will increase.
(C) This phenomenon is called ‘Natural Selection’. It is based on the ‘Theory of Evolution’ proposed by Charles Darwin.
Question: Mention the function of cellular DNA. Taking tallness as a characteristic for a plant, explain how proteins control the characteristic.
Answer: The major function of the DNA is to store information and pass it to offspring. It also directs the synthesis of proteins, which are necessary for a cell to perform its functions.
The part of DNA that provides information for protein synthesis is called gene. Proteins control specific characteristic or trait of an organism.
For example, a plant species has gene for the characteristic called ‘tallness’. Now, the gene for tallness will give orders to the plant cells to make a lot of plant growth hormones. Due to the formation of excess of plant growth hormones, the plant will grow tall.
If the plant has genes for dwarfness, then plant growth hormones production will be low. As a result, the plant will not grow tall and will remain short. The above examples explain how proteins control the characteristic.
Long Answer Type Questions:
Question: Gregor johon mendel was the first to give scientific explanation for the mechanism of transmission of characters from parents to the oppsprings. He is called the Father of Genetics. Mendel conducted hybridisation (cross breeding) experiments on Garden pea
Pisum in the garden of a monastry in Austria, continuously for eight years. He studied the inheritance of one character at a time and introduced the concept that each character is controlled by a factor. Mendel made a cross between pure breeding pea plants one with round and green seeds and the other with wrinkled and yellow seeds.
Answer the following questions on the basis of your understanding about mendel’s laws:
(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) In the given cross, two traits were taken into account, which is a dihybrid cross. The round shape and yellow colour of seed is dominant over the wrinkled shape and green colour of seed in pea plant as observed by Mendel.
Suppose R and Y denote dominant trait and r and y denote recessive trait. Genotype of the parent plant with round and green seeds – RRyy
Genotype of the parent plant with wrinkled and yellow seeds – rrYY Therefore, the cross involved in the given question is The above cross shows round and yellow seeds in the F1 generation. It occurs because dominant traits (round and yellow) express itself, whereas recessive traits (wrinkled and green) get suppressed.
(B) On selfing of F1 generation:
Phenotypic ratio 9:3:3:1
Round Round Wrinkled Wrinkled
yellow green yellow green
9 : 3 3 1
Question: (A) What is the law of dominance of traits?
Explain with an example.
(B) Why are the traits acquired during the life time of an individual not inherited?
Answer: (A) Law of Dominance of traits: Law of dominance is defined as when two homozygous individuals with one or more sets of contrasting characters are crossed, the F1 hybrids have both the contrasting genes of a pair but only one expresses and it does not allow the other to appear. The one that is expressed is dominant and the other which does not appear is recessive.
Monohybrid cross to explain the law of dominance. Mendel first crossed homozygous tall pea plants (TT) with homozygous dwarf pea plants (tt) and found
that only tall pea plants were produced in the first generation or F1 generation.
From this Mendel concluded that F1 generation showed the traits of only one of the parent plants. The trait of dwarfness did not show up.
The traits which were shown/ expressed were called dominant traits.
The traits which were not expressed was termed as recessive traits.
This phenomenon of appearance of only one of two contrasting traits in F1 generation, is termed as dominance.
The traits are not lost even when they are not expressed.
When F1 offsprings were self-pollinated, both the paternal traits were expressed.
Question: Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Provide a suitable explanation.
Answer: It is difficulttosaywhetherhumanbeingsare more evolved than bacteria or bacteria are more evolved than human beings. It depends on the way we evaluate evolution. If the appearance of complexity is concurrent with evolution, then human beings are certainly more evolved than bacteria. Bacteria have a cellular level of organization, whereas humans have organ level organization.
However, if evolution is viewed as the ability to survive in extreme conditions, then bacteria is more evolved as compared to human beings.
This is because bacteria can survive under the most extreme conditions. Many bacteria live in sulphur springs and in craters of volcanoes.
But the totality of life characteristics makes it hard to prove whether bacteria are less or more evolved organisms as compared to human.
Question: Name the plant Mendel used for his experiment. What type of progeny was obtained by Mendel in F1 and F2 generations when he crossed the tall and short plant?
Write the ratio he obtained in F2 generation plants.
Answer: Name of plant used by Mendel for his experiments was: Garden Pea (Pisum sativum) When Mendel crossed pure Tall plant having genotype ‘TT’ with pure dwarf plant having genotype ‘tt’, progeny obtained in F1 generation were all Tall.
Mendel then crossed the tall pea plants of the first generation and found that 75% or three quarter of the F2 progeny were tall and 25% or one quarter of them were short.
Ratio obtained in F2 generation:
Tall : Short = 3 : 1
TT : Tt : tt = 1 : 2: 1
Question: Give reasons for the appearance of a new combination of characters in the F2 progeny.
Answer: F1 plants have round and yellow seeds. In F1 generation, the dominant alleles suppress the recessive ones. So, as a result, only dominant alleles are expressed. Thus, all the progenies in the F1 generation; showed dominant traits only. However, genes for recessive traits were present in all the plants. When the F1 generation is crossed, it gives rise to new combinations in the F2 generation with round-yellow, round-green, wrinkled yellow and wrinkled-green in
the ratio of 9 3: 3: 1.
This indicates that the chances for the pea seed to be round or wrinkled do not depend on their chances to be yellow or green. Each pair of alleles is independent of the other pair. This is known as ‘principle of independent assortment’.
Question: All the human races like Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor. Provide a few evidences in support of this view.
Answer: All human beings have evolved from a common ancestor as they have the maximum number of common characters. Moreover, all human beings can interbreed with each other, which shows that all of them belong to the same species. Some of the common characters of all human beings are:
(1) Common body plan, structure, physiology and metabolism.
(2) All of them have a constant chromosome number i.e., 46.
(3) Their genetic makeup is also similar i.e., almost 99.9% DNA is nearly the same in all humAnswer:
(4) All the humans; can freely inter-breed to produce offspring.
All these evidences clearly indicate that all of us, whether Africans, Asians, Europeans, Americans, etc., have evolved from a common ancestor.
Question: Mention that total number of chromosomes along with the sex chromosomes that are present in a human female and a human male.
Explain how in sexully producing organisms the number of chromosomes in the progeny remains the same as that of the parents.
Answer: The total number of chromosomes in humans is 23 pairs (or 46 chromosomes). Out of this, the 23rd pair is sex chromosome.
The equal genetic contribution of male and female parents in a progeny is ensured through special type of reproductive cells called gametes. Gametes have only half the amount of DNA as compared to other body cells. So, when the gametes from male and female parents combine during sexual reproduction to form a zygote, they contribute equal amount of DNA.
Let us further understand it with the help of an example. The normal body cells of human beings contain 46 chromosomes each. Now, the human male gamete has 23 chromosomes and the human female gamete has also 23 chromosomes.
So, during sexual reproduction the combination of 23 chromosomes from male and 23 chromosomes from female ensures equal genetic contribution in the progeny, i.e., 23 + 23 = 46 chromosomes.
Question: Differentiate between inherited and acquired traits by giving one example of each. Give reason why the traits acquired during the life time of an individual are not inherited?
Question: (A) List two visible traits of garden pea that Mendel considered in his experiments.
How do Mendel’s experiments show that traits may be dominant or recessive?
(B) With the help of a flow diagram, how would you establish that in human beings
the sex of a newborn is purely a matter of chance and none of the parents may be considered responsible for a particular sex of a newborn child?
Answer: (A) Visible traits of garden pea that Mendel considered in his experiments were:
(1) Tall and dwarf plants.
(2) Round and wrinkled seeds
(3) Yellow and green colour of seeds
(4) Purple and white colour of flower
(5) Inflated and constricted shape of pod.
(6) Yellow and green colour of pod
(i) Mendel first crossed pure-breed tall pea plants (TT) with pure-breed dwarf pea plants (tt) and found that all plants in this first generation, or F1 progeny, were tall (Tt).
(ii) Mendel then crossed the tall pea plants (Tt) of the first generation and found that the second-generation, or F2, progeny of the F1 tall plants are not all tall. Instead, one quarter of them are short (tt).
(iii) This indicates that both the tallness (T) and shortness (t) traits were inherited in the F1 plants, but only the tallness trait (T), which was dominant, was expressed.
(iv) The dwarfness trait (t) which was inherited in the F1 progeny and not expressed but was later expressed in F2 progeny was the recessive trait.
(v) Thus, two copies of the trait are inherited in each sexually reproducing organism.
(B) The flow chart showing sex determination in human beings is given below:
The sex of a new born baby is therefore a matter of chance and none of the parents may be considered responsible for it as it is genetically determined.
Question: (A) What is variation? How is variation created in a population? How does the creation of variation in a species promote survival?
(B) Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes.
Answer: (A) The differences in characteristics between individuals of the same species is called variation. Variations arise in organisms during the process of copying the DNA due to which the DNA copies will be similar but not identical to the original.
Variation is created in a population consisting of sexually reproducing organisms as greater diversity will be generated over succeeding generations since it involves two parents, and there will always be subtle changes in DNA. So, there is accumulation of new combinations of variations as each generation inherits differences from its previous generation, along with the newly created differences.
Species having suitable variations have better chances of surviving in the event of sudden environmental changes.
(B) During the process of formation of germ cells in sexually reproducing organisms, meiosis cell division takes place in the reproductive organs due to which the male and female germ cells or gametes will have half the number of chromosomes as compared to their parent cells. When fertilization takes place by the fusion of the two germ cells, the normal number of chromosomes is thus restored in the progeny. So, the progeny will have the same number of chromosomes as its parents.
The total number of chromosomes in human beings is 23 pairs or 46 chromosomes out of this, the 23rd pair is sex chromosome.
Women have a perfect pair of sex chromosomes both called X chromosome.
Men have a mismatched pair’ XY. This human Male gamete has 23 chromosome (22 + X or 22 + Y) and the human female
gamete has also 23 chromosomes (22 + X): During fertilization, the normal number of chromosomes (46) is restored in the progeny.
Question: If we cross-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant, we will get plants of F1 generation. If we now self-cross the pea plant of F1 generation, 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.
Write the reason for the same.
Answer: (A) All plants of F1 generation are tall.
(B) Ratio of tall plants to dwarf plants in F2 generation = 3 : 1.
(C) Dwarf plants were not found in F1 generation but appeared in F2 generation. This indicates that both the tallness (T) and shortness (t) traits were inherited in the F1 plants, but only the tallness trait was expressed as it is a dominant trait, whereas the dwarfness trait was not expressed, though it was inherited, as it is a recessive trait. Both TT and Tt are tall plants, while only tt is a short plant. A single copy of ‘T’ is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.
Traits like ‘T’ are called dominant traits, while those that behave like ‘t’ are called recessive traits.
Question: How did Mendel interpret the results of his experiments to show that ‘‘the traits may be dominant or recessive”? Explain briefly.
Answer: Mendel crossed pure-bred tall pea plants (TT) with pure-bred dwarf pea plants (tt) and found that all plants of F1 progeny were tall.
When these F1 progeny are self crossed, he observed that the F2 progeny are not all tall. The ratio of tall plants to dwarf plants comes to be approximately 3 : 1.
This indicates that both the tallness (T) and shortness (t) traits were inherited in the F1 plants, but only the tallness trait was expressed.
Above experiment led Mendel to propose that two copies of factor (now called genes) controlling traits are present in sexually reproducing organisms.
Traits like ‘T’ are called dominant traits, while those that behave like ‘t’ are called recessive traits.
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?
In Mendel’s cross between round and wrinkled pea plant, the percentage of the plants in the 2 generation is 75%
Explanation: Mono hybrid cross between round and wrinkled pea plants
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.
(C) Explain in brief how Mendel interpreted his results to show that the traits may be
dominant or recessive.
Answer: (A) Mendel chose garden pea for his experiment because:
(1) Pea plant has short life cycle.
(2) Pea plant is small and easy to grow.
(3) In pea plant both (self and cross) pollination can be made possible.
(B) Contrasting characters of garden pea are:
(1) Round / wrinkled seeds (shape)
(2) Green/ yellow seeds (colour)
(3) Tall / Dwarf plant (height)
(C) When mendel crossed two pea plants with a pair of contrasting characters (shape, colour,height etc.) only one character appeared in all the members of F1 progeny, the other remains hidden.
On selfing, F1, the hidden characters reappeared in just 25% of the offsprings and the other 75% shared the characters expressed in F1. Mendel concluded that the character which express itself in F1 and 75% of the individual in F2 is dominating because they express their traits while other are recessive.
Question: With the help of Mendel’s experiments show that:
(A) traits may be dominant or recessive, and (B) traits are inherited independently.
Answer: (A) • Mendel crossed pure tall pea plants with pure short pea plants.
• All tall plants were produced in the Fgeneration.
• When F1 tall plants were self-pollinated, Mendel got both tall and short plants in the ratio of 3 Tall : 1 Short.
• This clearly indicated that tall character is dominant over short character which although present would not be expressed in F1 generation./
(B) When pea plants with two different characteristics like plants with round and green seeds and the plants with wrinkled and yellow seeds; were bred with each other, the F1 generation had plants with round and yellow seeds (dominant character). On self-pollination of F1 generation plants, F2 generation obtained was a mixture of round yellow, round green, wrinkled yellow and wrinkled green in the ratio 9:3:3:1, thus showing that the traits are inherited independently.
Question: How do Mendel’s experiments show that the (A) traits may be dominant or recessive,
(B) traits are inherited independently?
Answer: (A) When Mendel cross pollinated pure tall pea plants with pure dwarf pea plants, only tall plants were obtained in F1 generation. On self pollinating the F1 progeny, both tall and dwarf plants appeared in F2 generation in the ratio 3:1 Appearance of tall character in both the F1 and F2 shows that it is a ominant
character. The absence of dwarf character in F1 generation and its reappearance in F2 shows dwarfness is the recessive character.
(B) When Mendel conducted a dihybrid cross having two sets of characters, he obtained only one set of parental characters in F1 generation whereas in F2 generation he obtained both the set of parental characters now recombined in the ratio of 9:3:3:1.
The appearance of new recombinants in the F2 generation along with parental type shows that traits are inherited independently.
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 self- fertilised, 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) The dwarf traits of the plant is not expressed in the presence of the dominant tall trait.
(B) In the F2 generation, both the tall and dwarf traits are present in the ratio of 3 : 1. This showed that the traits for tallness and dwarfness are present in the F1 generation,but the dwarfness, being the recessive trait does not express itself in the presence of tallness, the dominant trait.
Question:Answer the following questions:
(A) Why did Mendel choose garden pea plant for his experiments? Write two reasons.
(B) List two contrasting visible characters of garden pea Mendel used for his experiment.
(C) Explain how Mendel interpreted his results to show that the traits may be dominant or recessive.
Answer: (A) Mendel choose garden pea plant for his experiments because
(1) Pea plant has several contrasting characters like height, flower colour,seed colour and shape.
(2) Normally allows self pollination but cross pollination can also be done.
(3) It has short life span and also is easy to cultivate.
(B) Contrasting characters of garden peaplants:
Colour of seeds:
Dominant – Yellow Recessive – Green Shape of seeds:
Dominant – Round Recessive – Wrinkled.
(C) Mendel took pea plants with different characteristics – a pure breed tall plant and a pure breed dwarf plant. Pure breed plant means, both versions of a trait are identical.
(1) Pure tall pea plant (TT) – Both trait T are identical, which represents tallness in the plant.
(2) Pure dwarf pea plant (tt) – Both trait t are identical, which represents dwarfness in the plant.
He produced progeny from them by cross pollination of TT and tt plants and calculated the percentages of tall or short progeny. He observed that
all F1 generations of plants were tall.
Mendel allowed only self-pollination in F1 progeny.
He found that in F2 progeny 75% plants were tall (TT or Tt) and only 25% plants were dwarf (tt).
The result of his experiment shows that trait may be dominant or recessive.