CBSE Class 10 Biology Heredity Worksheet Set I

ONE MARK QUESTIONS

Question: Why is it that asexual reproduction produces exact copies but sometimes minor variations are also seen in next progeny?
Answer: Since no biochemical reaction is reliable, therefore, in copying of DNA, it may cause slight difference which causes these variations.

Question: A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the result in Fj progeny?
Answer: All will bear violet flowers.

Question: Why is the progeny always tall when a tall pea plant is crossed with a short pea plant?
Answer: The trait which represents the tallness in a pea plant is dominant over the another trait, shortness (dwarf).

Question: How many pairs of chromosomes are present in human beings?
Answer: 23 pairs.

Question: What indication do we get by reappearance of dwarf plant in F₂ generation?
Answer: After obtaining progeny in F₂ generation in a dihybrid cross, Mendel concluded that when two pairs of traits are combined in a hybrid, one pair of character segregates independently of the other pair of character.

Question: In a beetle population, the number of green beetles is more than blue and red beetles. Give a reason behind this situation.
Answer: Variation/Natural selection.

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
b. Species

Question: What is a gene?
Answer: It is a functional piece of DNA that is responsible for expression of a trait in the organisms.

TWO MARKS QUESTIONS

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: What are fossils? What is their significance in the study of evolution?
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.
a. Study of fossils helps in working out evolutionary relationships.
b. 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.
c. Age of fossils can also be found by time dating using isotopes of carbon! carbon dating.
d. By studying fossils occurring in different strata of rocks, geologists are able to reconstruct the time course of evolutionary events.

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

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: 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: 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: 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)

THREE MARKS QUESTIONS

Question: What is evolution? How does it occur?
Answer: rganic 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: Discuss the role of variations in evolution. What is natural selection and genetic drift? 
or
Explain the following:
(a) Speciation (b) Natural Selection
Answer: a. The members of a population have minor differences among them which is called variations.
b. Two sources of variations are sexual reproduction and environmental factors.
c. Sexual reproduction has greater chances of producing variation.
d. Variations with some advantage has greater chances of surviving, for example, long neck of giraffe.
e. Natural selection and genetic drift lead to formation of new species hence evolution.
Natural Selection: Some variations may have survival advantage hence they happen to gain over others so that they can propagate more than others. Ultimately such variations are selected and propagated among all members of the population.
This is called adaptation of the species which help them to cope well in their surroundings.
In course of time, it could lead to accumulation of adaptation. In geographically separated populations of a species and development of reproductive barrier among them may lead to the formation of a new species.
Genetic Drift: Some variation may not give survival advantage to members of population.
But if by chance other variations are wiped out from populations, the remaining variations get propagated in next generations.

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: 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 dominant 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: a. 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. No, the structure of the eye in each of the organisms is different.
b. Fossils of certain dinosaurs/reptiles show imprints of feathers along with their bones but they could not fly presumably using the feathers for insulation.
Later they developed / evolved and adapted feathers for flight, thus becoming the ancestors of present day birds.
(OR any other suitable evidence/example)

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: 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 function is performed by human arms, forelimbs of dog and forelimbs of whales?
b. Which type of organs are these?
c. Why do we call them so?
Answer: a. Human arm : holding things Forelimbs of dog :
running Forelimbs of whales : paddles
b. Homologous,
c. Same origin, different functions.

Question: An angiosperm plant having red coloured flowers when crossed with the other having the same colour produced 40 progenies, out of which 30 plants were with red coloured flowers, 10 plants were with white coloured flowers. Find out:
a. What is the possible genotype of parent plants?
b. Which trait is dominant and recessive?
c. What is this cross called as and what is its phenotypic ratio?
Answer: a. Rr and Rr.
b. Red colour of flowers is the dominant trait while white colour is the recessive trait.
c. Monohybrid cross, phenotypic ratio is 3 : 1.

Question: If a population of red beetles, living on green bushes,
is being eaten by crows. During sexual reproduction,
a green beetle is found in progeny:
a. What is the future of new trait?
b. Will it survive in the new habitat?
Answer: a. Among progeny, when green beetle is found, it escaped attack of crows as it merged with green colour. Green beetles increased, red decreased.
b. New trait will survive.

Question: Explain with an example for each, how the following provides evidences in favour of evolution in organisms:
a. Homologous organs
b. Analogous organs
c. Fossils
Answer: a. Homologous organs – study of homologous organs suggests that the organs having same structure but performing different functions have evolved from a common ancestor. Example: forelimbs of a frog, lizard, bird and man.
b. Analogous organs – show adoption of organs for common use. Example: wings of butterfly and wings of bat.
c. Fossils – provide the missing links between two species. Example: – Archeopteryx / fossils of some dinosaurs with feathers.

FIVE MARKS QUESTIONS

Question: Give five points to show the significance of variations.
Answer: a. Variations help an organism to get adapted to the changing environment.
b. Variations lead to evolution through natural selection and adaptation.
c. During sudden change in the environment only those variants will make the population of that particular species which can withstand such changes.
d. Variations result in more genetic vigour, i.e., organism emerges as a strong species maintaining its large population.
e. Variations make an organism to be resistance to diseases and environmental fluctuations.

Question: In a pea plant, find the contrasting trait if:
a. the position of flower is terminal.
b. the flower is white in colour.
c. shape of pod is constricted.
Answer:
a. Axial position of flower.
b. Purple colour of flower.
c. Inflated shape.

Question: A pea plant with blue colour flower denoted by BB is cross-breed with a pea plant with white flower denoted by ww.
a. What is the expected colour of the flowers in their F1 progeny?
b. What will be the percentage of plants bearing white flower in F2 generation, when the flowers of F1 plants were selfed?
c. State the expected ratio of the genotypes BB and Bw in the F2 progeny.
Answer:
a. F1 generation — blue.
b. 25%
c. BB : Bw = 1 : 2.

Question: What are chromosomes ? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.
Answer: Chromosomes – Thread like structures made up of DNA found in the nucleus. The original number of chromosomes becomes half during gamete formation.
Hence, when the gametes combine, the original number of chromosomes gets restored in the progeny.
(or same thing explained in the form of a flow chart).

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: Woman are often blamed for bearing daughters. As a student with knowledge in science how will you explain it to your fellow students that the sex of the child is not determined by mother’s genetic contribution?
Answer: Sex of the child is not determined by mother’s genetic contribution. The sex is determined by a specific pair of 7 chromosomes called sex-chromosomes. In female, this pair consists of two similar (homologous) chromosomes denoted as XX. Hence, females produce only one type of gametes (Ova/eggs) each having an ‘X’ chromosome.
Whereas male human being has two different types of sex chromosomes i.e., X, Y (heterologous) having different sizes and shapes. Hence male produces two different kinds of gametes (sperms). Half of them have “X’ chromosome and half have ‘Y’ chromosome.
If a sperm with ‘X’ fuses with the ovum, female child is born and if a sperm with ‘Y’ chromosome fuses with the ovum, male child is bom as shown below in the cross. Therefore, the father’s genes is responsible for the determination of the sex of the child.

Question: (a) “Each organism has its own identity”. Explain.
(b) What is speciation?
Answer: 
a. (i) The DNA of each organism is different from others.
(ii) The DNA of each organism is specific within the same species with specific number of chromosomes/genes.
b. Emergence of new species from pre-existing forms through natural selection/artificial selection/ genetic drift/evolution, etc. 

Question: (a) Explain giving examples how artificial selection has helped in the formation of newer varieties of cauliflower.
(b) List the steps involved in the formation of new species.
(c) How different races of human beings belong to the same species?
Answer: 
a. Formation of newer varieties, e.g., Broccoli, cauliflower, red cabbage, etc. by man.
b. Migration, gene flow, natural selection, new species.
c. Capable of interbreeding among themselves.

Question: How are fossils formed? Describe, in brief, two methods of determining the age of fossils.
Answer: Fossils are formed when dead organisms are not completely decomposed. The organisms may get trapped in resins of tree, lava of volcanoes or hot mud which when hardens, retains the animal’s parts thus, forming fossils.
Two methods of determining the age of fossils:
a. Relative method: By estimating the age of the layer of earth’s crust where the fossil is found.
Fossils near the surface are recent and those in the deeper layers are more ancient.
b. Radio-carbon dating method: By detecting the ratios of different isotopes of carbon in the fossils.
Fossils help in determining the connecting links between various groups and their origin from their primitive ones, e.g., Archaeoptyrx.

Question: What is speciation? Discuss any two factors that lead to speciation.
Answer: Speciation means creation of new species from pre exiting ones. The two main factors which could lead to the formation of a new species are natural selection leading to accumulation of adaptation in geographically separated populations of a species and development of reproductive barrier among them.
Complete separation of sub-populations of a spices (Genetic drift) and difference in way of Natural selection in them for many generations results in speciation i.e. formation of new species that cannot interbreed under natural conditions.

Question: List three main factors responsible for the speciation and briefly describe each one of them.
Answer: Genetic Drift: Random change in the frequency of genes. 
Natural Selection: Nature selects the fittest individual in a population. Reproductive Isolation: When two individuals are geographically isolated and natural selection operates upon them differently leading to inability of the individuals to interbreed.