CBSE Class 10 Science Heredity and Evolution Assignment Set A

MCQ Questions for NCERT Class 10 Science Heredity and Evolution

Question. In a monohybrid cross done by Mendel
(a) F1 had 75% tall plants and 25% dwarf plants
(b) F1 had all tall plants
(c) F1 had all dwarf plants
(d) none of the above was observed
Answer : B

Question. Which of the following constitutes an example of Homologous organs?
(a) Wings of bat and wings of butterfly
(b) Forelimbs of horse and wings of bat
(c) Eyes of insects and eyes of man
(d) Legs of cockroach and hindlegs of frog
Answer : B

Question. Mendel was
(a) an Englishman
(b) an American
(c) a German
(d) an Austrian
Answer : D

Question. What was used by Mendel for his experiments?
(a) Fruit flies
(b) Pea plant
(c) Rice plant
(d) Rabbits
Answer : B

Question. What does a dominant character mean?
(a) It is expressed first.
(b) It suppresses the recessive character.
(c) It remains unaffected by the recessive character.
(d) All of the above
Answer : D

Fill in The Blank

Question. In a monohybrid cross, one of the alleles is ...... and another, ...... .
Answer : dominant, recessive

Question. DNA is hereditary material because it is ...... and ...... .
Answer : replicated, transmitted

Question. As it stands today, characters ...... are not inherited, and in this regard theory of ...... is not sustainable.
Answer : acquired, Lamarck

Question. Mutation is generally ...... to animals.
Answer : beneficial

Match The Columns

                A                                             B
(i) Natural selection                            (a) Lamarck
(ii) Inheritance of acquired characters  (b) Phenotype
(iii) Homozygous condition                  (c) Darwin
(iv) Physical traits                              (d) Molecular phylogeny
(v) Study of DNA sequence                 (e) TT

Answer : (i)(c)  (ii)(a)  (iii)(e)  (iv)(b)  (v)(d)

Very Short Answer Question

Question. Who gave the first scientific theory of organic evolution?
Answer : Lamarck

Question. Define allele.
Answer : Unit factor responsible for genetic character, named by Mendel

Question. Name the book in which Darwinism is described.
Answer : Origin of Species

Assertion and Reason

DIRECTION : In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as:
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.

Question. Assertion : Although living organism always arise from other living organism,, life should certainly have had a beginning.
Reason : The study of the conditions and the
mechanisms involved in the creation of most primitive living structures on earth is actually the problem of origin of life.
Answer : A

Question. Assertion : Speciation is the process of formation of a new species from a pre-existing one.
Reason : Mutation plays a role in speciation.
Answer : A

Question. Assertion : Ear muscles of external ear in man are poorly developed.
Reason : These muscles are useful which move external ear freely to detect sound efficiently.
Answer : C

Question. Assertion : Wings of butterfly and wings of bat are analogous organs.
Reason : Analogous organs have different origin and structural plan but same function.
Answer : A

Question. Assertion : Fossils are remains of dead organisms.
Reason : It is helpful in study of evolution.
Answer : B

Question. Assertion : We have lost all the direct evidence of origin of life.
Reason : The persons responsible for protecting evidences were not skilled.
Answer : C

Question. Assertion : The genetic complement of an organism is called genotype.
Reason : Genotype is the type of hereditary properties of an organism.
Answer : A

Question. Assertion : Forelimbs of vertebrates are homologous organs.
Reason : Analogous organs have same origin but different functions.
Answer : C

Question. Assertion : Variations are seen in offspring produced by asexual reproduction.
Reason : DNA molecule generated by replication is not exactly identical to original DNA.
Answer : A

Question. Assertion : A geneticist crossed two pea plants and got 50% tall and 50% dwarf in the progeny.
Reason : One plant was heterozygous tall and the other was dwrf.
Answer : A

Heredity and Evolution

Question. How are fossil studies important in working out evolutionary relationships. How would the age of fossils be determined?
Answer : Fossils are impressions of the body/ body parts or the remains of organisms living in the past, which got preserved in sediments of earth. Any remains of an organism that has been preserved in the earth’s crust.Study of fossils helps in working out evolutionary relationships. Age of fossils can be determined by time dating using isotopes of carbon (carbon dating).

Question. a. How many gene sets should a germ cell have?
b. Mention two factors causing evolution.
Answer : 
a. One gene set.
b. (i) Reproduction isolation (ii) Natural selection

Question. Tails of some mice were amputated and they were allowed to breed. The mice that were produced also had their tails amputated and it was repeated for many generations. What is the reason of tail appearing again and again?
Answer :Such traits are acquired traits. Traits acquired during the life-time of an individual are not inherited as these changes are not in the genes of reproductive tissues.
The changes in the non-reproductive tissues cannot be passed on to the DNA of the germ cells, hence such acquired changes are not inherited by the progeny.
Example: tailless mice (if tail is removed by surgery) cannot produce tailless progeny.

Question. In an area A, the leaf materials available to beetles were very less. What are the two consequences seen in case of beetles?
Answer : a. Due to poor nutrition, the average weight of adult beetles decreases.
b. The number of beetles (population) decreases due to starvation.

Question.“The chromosome number of the sexually producing parents and their offspring is the same”. Justify this statement.
Answer :  In sexual reproduction, both the gametes (male and female) contain half the number of chromosomes (haploid or n) and by the fusion of these gametes, the zygote have full set (diploid 2n) chromosomes.

Question. What is the importance of DNA copying in reproduction? Why is variation beneficial to the species but not necessary for the individual? Explain.
Answer : DNA copying is essential part of reproduction because it ensures that same blueprint of the body design is maintained. Variation for the species is beneficial for
adaptation and better survival. It may result in new species formation.

Question. How did Mendel explain that it is possible that a trait is inherited but not expressed in an organism?
Answer : Yes, it is possible.
Example - When pure tall pea plants are crossed with pure dwarf pea plants, only tall pea plants are obtained in F1 generation.
On selfing tall plants of F1 both tall and dwarf plants are obtained in F2 generation in the ratio 3:1.
Reappearance of the dwarf character, a recessive trait in F2 generation shows that the dwarf trait/character was present in individuals of F1 but it did not express (due to the present of tallness, a dominant trait / character)

Question. What is evolution? How does it occur?
Answer : Organic Evolution: Gradual unfolding of organisms from pre-existing organisms through change is called evolution.
a. Evolution occurs in the form of genetic drift and natural selection combined with geographical separation.
b. Speciation - evolution of a new species from preexisting species-occurs.
c. Fossils are impressions of the body/body parts or the remains of organisms living in the past, which got preserved in sediments of earth.
d. Study of not living species but also fossils helps in working out evolutionary relationships.
e. Fossils provide one of the most acceptable evidences in support of evolution, because we can study the evolutionary past of individuals in the form of their fossils.

Question.How can we say that change in genes can be brought about the change in DNA?
Answer : A gene is a segment of DNA on a chromosome occupying a specific position.
a. It provides informations from one protein to another and is responsible for its alteration.
b. It ensures the stability of the DNA of the species.
So, we can say that change in gene segment can bring about change in DNA.

Question.What is micro evolution? Does it explain speciation?
Answer :
a. In micro evolution, the changes are small which occurs in lower categories and change the common characteristics of a particular species.
b. It does not properly explain speciation. 

Question. Where are the genes located? What is the chemical nature of gene?
Answer :Genes are located on chromosomes in linear sequence and at fixed positions. Chemically, genes are acidic in nature since they are nucleic acids which constitute DNA.

Question. What is F₂ generation?
Answer : The generation produced by the offsprings of F1
generation i.e., first generation as parent is called F2

Question. a. Write full form of DNA.
b. Why are variations essential for the species?
Answer :
a. Deoxyribonucleic acid
b. Survival 

Question. What are sex chromosomes? Which sex chromosomes are found in male and female human beings? State the chromosome responsible for the development of male child in human beings?
Answer : Sex chromosomes are set of chromosomes present in human beings which help in sex determination.
XX and XY.
Y chromosome. 

Question. Variations are important for the survival of species overtime. Justify this statement with reasons.
Answer : 
a. It causes adaptations,
b. It promotes natural selection.

Question. a. Do eyes of octopus, insect and human show relation in their evolutionary process?
b. How can we say that birds have evolved from reptiles?
Answer :
a. No, eyes of these animals do not show any evolutionary relationship as they are analogous organs.
b. The presence of feathers both in dinosaurs and birds indicate birds have evolved from reptiles.Some organs may be adapted to perform new functions during evolution, e.g., feathers which were meant for providing insulation in cold weather, slowly became adapted for flight. Hence birds are closely related to reptile as dinosaurs had feathers, though could not fly. 

Question.Explain how gene expresses itself in a cell? Why are we somewhat similar to our parents yet not identical to them?
Answer :Genes are functional segments of DNA. They are units of heredity that gets passed on through reproduction from parents to progeny. It is the blue print of life. DNA expresses itself through synthesis of proteins.Proteins make structures in our body and also controls the functioning. In other words cells, tissues, organs and hence a living body expresses the traits inherited as genes/ DNA. Since we inherit the DNA, half from one and half from other parents, hence we somewhat resemble them. At the same time we show mixed traits of both so can not be identical to either of them.

Question. a. What is the genetic constitution of human sperm?
b. Mention the chromosomes pair present in zygote determining the sex of a male child.
Answer : a. 22 + Y or 22 + X
b. (22 + Y + 22 + X)

Question. “Natural selection and speciation lead to evolution”. Justify the statement.
Answer : Natural selection: Some variations are advantageous for an organism to adapt better in the prevailing conditions of habitat. It makes it easy to obtain food and mating partner by them. In this manner they are able to propagate more, transmitting their genes to next generation and producing more individuals with similar genetic makeup and phenotype.
a. It leads to change in frequency of some genes in a population which give survival advantage to a species from elimination.
b. When most of the members of a population possess this variation, it is called its adaptation.
c. Over a period of time large numbers of adaptations are accumulated in the various populations of a species which may be physically segregated from each other.
d. Geographical barriers like mountains, rivers etc., lead to incapability to reproduce amongst themselves in the population.
e. By processes like genetic drift and natural selection combined with geographical separation, when the populations of a species become incompatible/ fail to reproduce with each other, speciation- evolution of a new species from pre-existing species - occurs.

Question. If YYRR is round yellow, what do the following represent?
yyrr yyRR
Answer : yyrr - Wrinkled, green seeds
yyRR — Round, green seeds

Question. “Two areas of study namely evolution and classification are interlinked”. Justify this statement.
Answer : All living things are identified and categorised on the basis of their body design in form and function. After a certain body design comes into existence, it will shape the effects of all other subsequent design changes simply because it already exists. So, characteristics which came into existence earlier are likely to be more basic than characteristics which have come into existence later.
This means that the classification of life forms will be closely related to their evolution. On connecting this idea of evolution to classification, it is seen that some groups of organisms with ancient body designs have not changed very much. However, other groups of organisms have acquired their particular body designs relatively recently. Because there is a possibility that complexity in design will increase over evolutionary time, it may not be wrong to say that older organisms are simpler, while younger organisms are more complex.

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. (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.

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. How is the sex of child determined in human beings?
Answer : In human beings, sex of the child depends upon which kind of male gamete fertilizes the female gamete. If sperm carrying X chromosomes fertilizes the ovum carrying X chromosome, then the child born will be a girl. If a sperm carrying Y chromosome fertilizes the ovum which carries X chromosome, then the child born will be a boy.

Question. How did Mendel’s experiments show that different traits are inherited independently? Explain
Answer : Mendel crossed pea plants having round green seeds (RRyy) with pea plants having wrinkled yellow seeds (rrYY).
Since the F1 plants are formed after crossing pea plants having green round seeds and pea plants having yellow wrinkled seeds, F1 generation will have both these characters in them.However, as we know that yellow seed colour and round seeds are dominant characters, therefore, the F1 plants will have yellow round seeds. Then this F1 progeny was self-pollinated and the F2 progeny was found to have yellow round seeds, green round seeds, yellow wrinkled seeds and green wrinkled seeds in the ratio of 9:3:3:1

Question. In pea plant, round seed is dominant over the wrinkled. If a cross is carried out between these two plants, the genotype ratio of F2 progeny obtained from this cross is
(a)1:1
(b)3:1
(c)1:2:1
(d)9:3:3:1
Answer : Correct option(c)

Question. Newly formed DNA copies may not be identical at times. Give one reason.
Answer : If there is error in DNA copying/inaccuracies in DNA copying.

Question.What is the probability that the male progeny will be a boy?
(a) 50%
(b) 56%
(c) 47.43%
(d) It varies
Answer : Correct option (a)

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 generation with the help of a cross following the rules of inheritance of traits. State the visible characters of F1 and F2 progenies?
Answer : Let purple trait be represented by:PP and White trait be:pp

Visible characters of F1 progeny are all flowers are purple coloured and in F2 progenies 3 are purple coloured and 1 is white flower. 

MCQ Questions for Class 10 Science Heredity & Inheritance : -

Question. Define ‘evolution’. State Darwin’s theory of evolution.
Answer : Evolution is a change in the genetic composition of a population.
Darwin’s theory
1. The size of population remains the same, constant despite the fact that more offsprings are produced than needed.
2. Variations provide adaptations.
3. The best adapted organism survive in the changing environment (survival of the fittest).
4. Nature selects the best organisms with better adaptations and after many generations new species are formed (natural selection).

Question. Explain the analogous organs and homologous organs Identify the analogous and homologous organ amongst the following: Wings of an insect, wings of a bat, forelimbs of frog, forelimbs of human.
Answer : Analogous organs are those organs that have same function but have different structural design and origin. E.g., wings of birds and insects.
Homologous organs are those organs in different plants or animals which have the same basic structural design and organ but have different appearance and functions. Analogous—Wings of an insect, wings of a bat Homologous–Forelimbs of frog, forelimbs of human and wings of bat.

Question. What are various evidences in factors of evolution?
Answer : Evidences are:
(a) Homologous organs: Organs which have same structure but different function.
E.g., wings of a bat, hands of man and limbs of monkey.
(b) Analogous organ. Organs which perform similar function but are structurally different are called analogous organ. E.g., wings of bat, insects, birds.
(c) Vestigial organs: These organs are those which appear in an organism but are functionless e.g., vermiform appendix, nictitating membrane in eye is present in human beings but has no function.
(d) Embryological evidence: The study of embryos of vertebrates shows that all of them have same origin as their structure at initial stage is same. Embryo of frog, fish, man looks alike.
(e) Fossils as evidence: Archaeopteryx fossils shows a link between bird and reptiles as this fossil has some feature of bird and some of reptile.

Question. (i) What is genetics?
(ii) Give the common name of the plant on which Mendel performed its experiments.
(iii) What for did Mendel use the term factors and what are these factors called now?
(iv) What are genes? Where are the genes located?
Answer : (i) Science which deals with the study of heredity and variations is called genetic.
(ii) Pea plant.
(iii) Mendel used the term factors for ‘genes’.
(iv) Genes is the unit of inheritance. It is a part of the chromosome which controls the appearance of a set of hereditary character.
Genes are located on the chromosome.

Question. (i) What are traits?
(ii) Explain the inherited trait and acquired traits.
(iii) Define speciation. What are the factors which could lead to the rise of a new species?
Answer : (i) Traits: A characteristic feature is called trait.
(ii) Inherited and acquired trait (given in notes on page 112).
(iii) Speciation and factors (given in notes on page 112).

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