CBSE Class 10 Biology Heredity and Evolution Worksheet Set C

Question. The maleness of a child is determined by
(A) The X chromosome in the zygote.
(B) The Y chromosome in zygote.
(C) The cytoplasm of germ cell which determines the sex.
(D) Sex is determined by chance. 

Answer : B

Question. A cross between a tall plant (TT) and short pea plant (tt) resulted in progeny that were all tall plants because
(A) Tallness is the dominant trait.
(B) Shortness is the dominant trait.
(C) Tallness is the recessive trait.
(D) Height of pea plant is not governed by gene ‘T’ or ‘t’. 

Answer : A

Question. If a round, green seeded pea plant (RRyy) is crossed with wrinkled, yellow seeded pea plant, (rrYY) the seeds produced in F1 generation are :
(A) Round and yellow.
(B) Round and green.
(C) Wrinkled and green.
(D) Wrinkled and yellow. 

Answer : A

Question. The number of pair (s) of sex chromosomes in the zygote of humans is:
(A) One.
(B) Two.
(C) Three.
(D) Four. 

Answer : A

Question. A zygote which has an X-chromosome inherited from the father will develop into a
(A) Boy.
(B) Girl.
(C) X- chromosome does not determine the sex of a child.
(D) Either boy or girl. 

Answer : B

Question. Which of the following statement is incorrect?
(A) For every hormone there is a gene.
(B) For every protein there is a gene.
(C) For production of every enzyme there is a gene.
(D) For every molecule of fat there is a gene. 

Answer : D

Question. Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be
(A) Double fertilization.
(B) Self-pollination.
(C) Cross fertilization.
(D) No fertilization. 

Answer : C

Question. Assertion (A): Mendel choose a number of varieties of garden pea as plant material for his experiments.
Reason (R): Garden pea has well defined characters and is bisexual.

Answer : A

Question. Assertion (A): Mendel proposed the law of inheritance of traits from the first generation to the next generation.
Reason (R): Mendel’s Law of segregation is also known as “Law of purity of gametes.

Answer : B

Question. Assertion: A zygote with two X chromosomes develops into a boy.
Reason: If the egg cell carrying an X chromosome fuses with the sperm carrying a Y chromosome, the resulting child would be a boy.

Answer : D

Question. Assertion: A geneticist crossed a pea plant having violet flowers with a pea plant having white flowers, he got all violet flowers in first generation.
Reason: White colour gene is not passed on to next generation. 

Answer : C

Question. Assertion (A): Mendel in his experiment selected only two characters of seed.
Reason (R): He studied single character at one time.

Answer : D

Question. Assertion (A): In humans, males play an important role in determining the sex of the child.
Reason (R): Males have two X chromosomes.

Answer : C

Question. What is DNA?
Answer : DNA is the carrier of hereditary information from parents to the next generation. 

Question. What is a gene?
Answer : Gene is a part of DNA that encodes the instructions that allow a cell to produce a specific protein or enzyme. 

Question. Name the information source for making proteins in the cells. 
Answer : Cellular DNA is the information source for making proteins in cells. 

Question. Where is DNA found in a cell?
Answer : DNA is found in the cell nucleus. 

Question. Mendel took tall pea plants and short pea plants and produced F₁ progeny through crossfertilisation.
What did Mendel observe in the F₁ progeny? 
Answer : All pea plant were tall in F₁ generation. 

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

Question. A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the result in F₁ progeny? 
Answer : Violet flowers. 

Question. What is heredity?
Answer : The transmission of characteristics from one generation to another is known as heredity. 

Short Answer Type Questions :

Question. ‘Gene control traits’? Explain this statement with an example.
Answer : Gene controls the trait by synthesizing the specific enzyme. Consider tallness as a trait. Plant height depends upon particular plant hormone which in turn will depend on the efficiency of the process for making it. If the enzyme responsible for the production of this hormone is efficient, plant will be tall. If the gene for that enzyme has an alteration that makes enzyme less efficient, the amount of hormone will be less and plant will be short. 

Question. After self-pollination in pea plants with round, yellow seeds, following types of seeds were obtained by Mendel:

Analyse the result and describe the mechanism of inheritance which explains these results.
Answer : The ratio obtained is 9:3:3:1 in which parental as well as new combinations are observed. This indicates that progeny plants have not inherited the whole set of genes from each parent.
Every germ cell takes on chromosome from the pair of maternal and paternal chromosomes.
When two germ cells combine, segregation of one pair of characters is independent of other pair of characters. 

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.
(i) What do the plants of F₁ generation look like? 
(ii) State the ratio of tall plant to dwarf plants in F₂ generation.
(iii) State the type of plants not found in F₁ generation but appeared in F₂ generation. Write the reason for the same. 
Answer : (i) Tall 
(ii) 3: 1
(iii) Dwarf 
Reason: Being a recessive trait, dwarfness can only be expressed in the recessive homozygous condition or in the absence of dominant trait.  

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.
Answer : Let purple trait be represented by: PP and White trait be: pp 

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 respective scientific terms used for studying:
(i) The mechanism by which variations are created and inherited and
(ii) The development of new type of organisms form from the existing ones. 
Answer : (i) Genetics is the study of mechanism by which variations are created and inherited.
(ii) Evolution is used for studying the development of new type of organisms from the existing ones. 

Question. ‘Different species use different strategies to determine sex of a newborn individual. It can be environmental cues or genetically determined.’
Explain the statement by giving example for each strategy.
Answer : Environmental Cue: (i) In some animals, the temperature at which fertilised eggs are kept determines whether the developing animal in egg is male or female.
(ii) In some animals like snail, individual can change sex.
Genetical Cue: A child who inherits an X-chromosome from her father will be a girl and one who inherits a Y- chromosome from the father will be a boy. 

Question. A green stemmed rose plant denoted by GG and a brown stemmed rose plant denoted by gg are allowed to undergo a cross with each other. 
(a) List your observations regarding:
(i) Colour of stem in their F₁ progeny
(ii) Percentage of brown stemmed plants in F₂ progeny if F₁ plants are self pollinated.
(iii) Ratio of GG and Gg in the F₂ progeny.
(b) Based on the finding of this cross, what conclusion can be drawn? 
Answer : (a) (i) Colour of the stem in F₁ progeny: All green

(ii) Percentage of brown stem: 25 

(iii) GG: Gg is 1: 2
(b) Based on the above cross, it can be concluded that green colour is dominant and get expressed in F₁ generation. The brown stem, which does not get express itself in the F₁ generation, is the recessive character. This is the law of dominance.

Question. How did Mendel interpret his result to show that traits may be dominant or recessive? Describe briefly. 
Answer : Mendel conducted breeding experiments on Pea plants.
(i) He selected pure breed tall and dwarf plants. 
(ii) He cross-pollinated these plants. 
(iii) In the F₁ generation, he obtained only tall plants. Tallness is the dominant trait. 
(iv) Then, he produced F₂ generation by self cross of hybrids / F₁. 
(v) He found that 3/4^th of the plants were tall and 1/4th were dwarf. 
(vi) The trait which remains hidden in F₁ generation plants is the recessive traits. 

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 plants? Write the ratio he obtained in F₂ generation plants. 
Answer : Mendel used Pisum sativum (Pea plant) for his experiment.
Mendel took a tall pea (TT) plant and a short pea (tt) plant. When he crossed both, the first filial generation (F₁) obtained were tall. When F₁ progeny was self-pollinated, all plants obtained in F₂ generation were not tall. Instead, three tall pea (dominant) plants and one short pea (recessive) plant was obtained.

Question. What is DNA copying? State its importance.
Answer : DNA replication or DNA copying is the process of producing two identical replicas from one original DNA molecule during cell division.
Importance of DNA Copying:
(i) DNA replication needs to occur so that during cell division, new cells will also have a copy of organism’s DNA.
(ii) DNA is necessary to make all the RNA and proteins needed for cells to carry out necessary reactions and cellular processes in order to survive. 

Question. “The chromosome number of the sexually reproducing parents and their offspring is the same.” Justify this statement. 
Answer : Male individual have 46 chromosomes but because the gametes are always haploid i.e., they have half the number of chromosomes; sperms will be haploid (23 chromosomes). Female individual also contains only 23 chromosomes in egg. It is the fusion of the sperm and egg which leads to an offsprings with 46 chromosomes. 

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 self cross of 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 : Yes, the scientist may arrive at the law of dominance according to which the trait that is expressed in the F₁ generation is the dominant trait, although both the dominant and recessive traits are present in the F₁ generation. In the F₂ generation the recessive traits is also expressed along with the dominant traits. 

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) Occurrence of differences between organisms is called variation.
New variation may arise during the process of DNA copying that already has variations accumulated from previous generations.
Combining variations from two or more individuals would thus create new combinations of variations.
Species having suitable variations have more chances of survival in case of change in environment conditions.
(b) In sexually reproducing organisms, male and female gametes/reproductive cells with only half the number of chromosomes (as in the parent cell) are produced. During fertilization, when male and female gametes fuse to give rise to a zygote, original number of chromosomes are restored.

Question. How do Mendel’s experiment show that traits are inherited independently?
Answer : (i) When a cross was made between a tall pea plant with round seeds and a short pea plant with wrinkled seeds, the F₁ progeny plants are all tall with round seeds. This indicates that tallness and round seeds are the dominant traits. 
(ii) When the F₁ plants are self-pollinated, the F₂ progeny consist of some tall plants with round seeds and some short plants with wrinkled seeds which are the parental traits. 
(iii) There were also some new combinations like tall plants with wrinkled seeds and short plants with round seeds. 
(iv) Thus, it may be concluded that tall and short traits and round and wrinkled seed traits have been inherited independently. 

Question. In humans, there is a 50% probability of the birth of a boy and 50 % probability that a girl will be born. Justify the statement on the basis of the mechanism of sex-determination in human beings.
Answer : In human beings, the genes inherited from our parents decide whether it will be a boy or girl. Women have a perfect pair of sex chromosomes (XX). But, men have a mismatched pair (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, and one who inherits a Y chromosome from him will be a boy. 

Question. Differentiate between dominant and recessive traits. 
Answer : (a) The character which gets expressed in the presence of its contrasting form is termed as dominant trait.
(b) The trait which remains unexpressed in the presence of its contrasting form is called recessive trait. 

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 plants, in the first generation, F₁ only tall plants appear.
(i) What happens to the traits of the dwarf plants in this case?
(ii) 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 : (i)

Due to the Presence of dominant tall trait, plant was not able to express Recessive dwarf trait.
Tall: Dwarf = 3: 1 ratio
(ii) 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. 

Long Answer Type Questions :

Question. (a) What are dominant and recessive traits?
(b) “Is it possible that a trait is inherited but may not be expressed in the next generation?” Give a suitable example to justify this statement. 
Answer : (a) Dominant Trait: The trait which expresses itself in F₁ (first) generation after crossing contrasting (opposite) trait is known as dominant character (trait). 
Recessive Trait: The trait which is not expressed itself in F₁ (first) generation after crossing contrasting (opposite) trait. 
(b) Yes 2

(∴ t is not expressed in this generation which is recessive trait.)

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) Reasons:
(i) Pea plant is small and easy to grow.
(ii) A large number of true breeding varieties of pea plant are available.
(iii) Short life cycle.
(iv) Both self and cross-pollination can be made possible. (Any two reasons) 
(b) Contrasting characters:
Round / Wrinkled seeds
Tall / Short plants
White / Purple flowers
Green / Yellow seeds (Or any other)
(c) When Mendel crossed two pea plants with a pair of contrasting characters, only one character appeared in all the members of F₁ progeny and the others remain 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 expresses itself in F₁ and in 75% of the individuals of F₂ is dominating while the other is recessive.
(Or same thing can be explained by using an example) 

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? Explain.
Answer : (a) Law of dominance of traits: It states that “When parents having pure contrasting characters are crossed then only one character expresses itself in F₁ generation. This character is the dominant character and the character which cannot express itself is called recessive character”.
Let us take an example of tall and dwarf in pea plant. When pure line tall (TT) plants were crossed with pure line dwarf (tt) plants, offspring were all heterozygous tall (Tt). The appearance of all Tall plants in the F₁ generation shows that tallness is the dominant character while dwarfness is the recessive character. The ratio of Tall to Dwarf in F₂ generation is 3: 1.

(b) Characters that a person acquires during one’s life time are known as acquired characters/traits. Such changes do not occur in the reproductive tissues. Changes in the non-reproductive tissues are not passed on to the DNA of the germ cells and therefore not inherited by the next generation. 

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 conducted a Monohybrid cross/ (crossed pure tall pea plants with pure dwarf pea plants) he observed only tall pea plants in the F₁ generation, but on self crossing of the F₁ progeny, both tall and dwarf pea plants were observed in F₂ generation in the ratio 3: 1. Appearance of tall character in F₁ and F₂ generations shows tallness to be a dominant character. But absence of dwarf character in F₁ and its reappearance in F₂ confirms that dwarfness is recessive character. 
(b) Mendel conducted a dihybrid cross and observed that though he started with two types of parents, he obtained four types of individuals in F₂. The appearance of new recombination in F₂ generations along with parental type characters showed that traits are inherited independently of each other.