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NCERT Exemplar Class 10 Science Chapter 9 Heredity and Evolution Solutions

NCERT Exemplar Solutions for Class 10 Science Chapter 9 Heredity and Evolution covers all the important questions and answers as well as advanced level questions. It helps in learning about the Accumulation of variation during reproduction, DNA copying, Heredity, Evolution, Speciation and geographical isolation.

The NCERT Exemplar solutions for class 10 science is very important for board exams. NCERT Exemplar Solutions for Class 10 Science Chapter 9 Heredity and Evolution is provided by our experts. They prepared the best solutions which help the students in understanding the solutions in an easy way. This chapters also covers the other topics like Evolution and classification, Fossils, Inherited traits, variations, stages of evolution and variation in generations.


Chapter Name

Chapter 9 Heredity and Evolution

Book Title

NCERT Exemplar for Class 10 Science

Related Study

  • NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution
  • Revision Notes for Class 10 Science Chapter 9 Heredity and Evolution
  • MCQ for Class 10 Science Chapter 9 Heredity and Evolution
  • Important Questions for Class 10 Science Chapter 9 Heredity and Evolution

Topics Covered

  • MCQ
  • Short Answers Questions
  • Long Answers Questions

NCERT Exemplar Solutions for Chapter 9 Heredity and Evolution Class 10 Science

Multiple Choice Questions

1. Exchange of genetic material takes place in
(a) vegetative reproduction
(b) asexual reproduction
(c) sexual reproduction
(d) budding

Solution
(c) Sexual reproduction

Apart from sexual reproduction other options are type of asexual reproduction where only single parent is involved. Hence exchange of genetic material takes place in sexual mode of reproduction.


2. 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 fertilisation
(b) self pollination
(c) cross fertilisation
(d) no fertilization

Solution
(c) cross fertilisation


3. 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’. 

Solution
(a) tallness is the dominant trait

Only dominant characters are expressed in first progeny in monohybrid cross.


4. 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

Solution
(d) For every molecule of fat there is a gene

Fats are not controlled by genes but every protein enzymes and hormones are controlled by specific gene.


5. If a round, green seeded pea plant (RR yy) is crossed with wrinkled, yellow seeded pea plant, (rr YY) the seeds produced in F1 generation are
(a) round and yellow
(b) round and green
(c) wrinkled and green
(d) wrinkled and yellow

Solution
(a) round and yellow

As round and yellow are the dominant characters in F1 generation, all the seeds will be round and yellow.


6. In human males all the chromosomes are paired perfectly except one. This/these unpaired chromosome is/are
(i) large chromosome
(ii) small chromosome
(iii) Y-chromosome
(iv) X-chromosome 

(a) (i) and (ii)
(b) (iii) only
(c) (iii) and (iv)
(d) (ii) and (iv)

Solution
(c) (iii) and (iv)

These are sex chromosomes that are not paired perfectly due to half size of Y chromosom.


7. 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

Solution
(b) the Y chromosome in zygote

The zygote develops into a male child if sperm with Y chromosome fertilize the egg. If sperm with X chromosome fertilize the egg zygote will develop into female child.


8. 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

Solution
(b) girl

If sperm with Y chromosome fertilize the egg zygote will develop into male child. If sperm with X chromosome fertilize the egg zygote will develop into female child.


9.  Select the incorrect statement
(a) Frequency of certain genes in a population change over several generations resulting in evolution
(b) Reduction in weight of the organism due to starvation is genetically controlled
(c) Low weight parents can have heavy weight progeny
(d) Traits which are not inherited over generations do not cause evolution

Solution
(b) Reduction in weight of the organism due to starvation is genetically controlled

Weight loss and gain are controlled by external factors.


10. New species may be formed if
(i) DNA undergoes significant changes in germ cells
(ii) chromosome number changes in the gamete
(iii) there is no change in the genetic material
(iv) mating does not take place

(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii), (iii) and (iv)
(d) (i), (ii) and (iii)

Solution
(a) (i) and (ii)

Without change and variation the genetic material, evolution cannot take place.


11. Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce F1 progeny that have round, yellow (RrYy) seeds. When F1 plants are selfed, the F2 progeny will have new combination of characters. Choose the new combination from the following (i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green 

(a) (i) and (ii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (i) and (iii)

Solution
(c) (ii) and (iii)


12. A basket of vegetables contains carrot, potato, radish and tomato. Which of them represent the correct homologous structures?
(a) Carrot and potato
(b) Carrot and tomato
(c) Radish and carrot
(d) Radish and potato

Solution
(c) Radish and carrot

They both have similar structure and they both growth beneath the earth.


13. Select the correct statement
(a) Tendril of a pea plant and phylloclade of Opuntia are homologous
(b) Tendril of a pea plant and phylloclade of Opuntia are analogous
(c) Wings of birds and limbs of lizards are analogous
(d) Wings of birds and wings of bat are homologous

Solution
(a) Tendril of a pea plant and phylloclade of Opuntia are homologous

Because of similar design and origin, tendril of a pea plant and phylloclade of opuntia are homologous.


14. If the fossil of an organism is found in the deeper layers of earth, then we can predict that
(a) the extinction of organism has occurred recently
(b) the extinction of organism has occurred thousands of years ago
(c) the fossil position in the layers of earth is not related to its time of extinction
(d) time of extinction cannot be determined

Solution
(b) the extinction of organism has occurred thousands of years ago
Older fossils are found deep in the earth.

15. Which of the following statements is not true with respect to variation?
(a) All variations in a species have equal chance of survival
(b) Change in genetic composition results in variation
(c) Selection of variants by environmental factors forms the basis of evolutionary processes.
(d) Variation is minimum in asexual reproduction

Solution
(a) All variations in a species have equal chance of survival

Only the useful variations have chances of survival. Nature choose the fittest variation to survive.


16. A trait in an organism is influenced by
(a) paternal DNA only
(b) maternal DNA only
(c) both maternal and paternal DNA
(d) neither by paternal nor by maternal DNA

Solution
(c) both maternal and paternal DNA

As the DNA is contributed to an offspring by both the parents, the traits are contributed by both the parents.


17. Select the group which shares maximum number of common characters
(a) two individuals of a species
(b) two species of a genus
(c) two genera of a family
(d) two genera of two families

Solution
(a) two individuals of a species

Species is the lowest taxon hence members of same species share maximum number of common characteristics.


18. According to the evolutionary theory, formation of a new species is generally due to
(a) sudden creation by nature
(b) accumulation of variations over several generations
(c) clones formed during asexual reproduction
(d) movement of individuals from one habitat to another

Solution
(b) accumulation of variations over several generations

Variation in the DNA for several generations leads to the formation of new species. No gamete formation takes place in asexual reproduction, hence it will not result in variations. Movement of individuals from one habitat to another will not affect DNA change.


19. From the list given below, select the character which can be acquired but not inherited
(a) colour of eye
(b) colour of skin
(c) size of body
(d) nature of hair

Solution
(c) size of body

The nature of the body is decides by a person’s food. Regular exercise helps in building muscular body. The size of the body is not inherited as body nature is not transferred to offsprings.


20. The two versions of a trait (character) which are brought in by the male and female gametes are situated on
(a) copies of the same chromosome
(b) two different chromosomes
(c) sex chromosomes
(d) any chromosome

Solution
(b) two different chromosomes

This is the reason why one progeny expresses one version and other versions is expressed in another progeny.


21. Select the statements that describe characteristics of genes
(i) genes are specific sequence of bases in a DNA molecule
(ii) a gene does not code for proteins
(iii) in individuals of a given species, a specific gene is located on a particular chromosome
(iv) each chromosome has only one gene 

(a) (i) and (ii)
(b) (i) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)

Solution
(b) (i) and (iii)

Statement ii) is wrong because genes code for specific proteins. Statement 4 is wrong because chromosomes have many number of genes.


22. In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F2 is
(a) 1 : 3
(b) 3 : 1
(c) 1 : 1
(d) 2 : 1

Solution
(b) 3 : 1

The following genotypes would be produced if a cross between pure tall plant (TT) and short plant (tt) is made:
TT(Pure tall), tt( Pure short) andTt ( Mixed tall).
This makes the ratio between tall and short plants is 3:1.


23. The number of pair (s) of sex chromosomes in the zygote of humans is
(a) one
(b) two
(c) three
(d) four

Solution
(a) one

The sex of the offspring is determined by the 23rd pair of chromosome, hence it is called as sex chromosome.


24.  The theory of evolution of species by natural selection was given by
(a) Mendel
(b) Darwin
(c) Morgan
(d) Lamarck

Solution
(b) Darwin

Mendel proposed laws of heredity. Morgan discovered mutation in drosophila. Lamarck proposed use and disuse theory.


25. Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution this means that
(a) reptiles have evolved from birds
(b) there is no evolutionary connection between reptiles and birds
(c) feathers are homologous structures in both the organisms
(d) birds have evolved from reptiles

Solution
(a) reptiles have evolved from birds

Dinosaurs had feathers but they could not fly. Later birds adapted the feathers for flight. As, dinosaurs were reptiles, this means that birds have evolved from them.


Short Answer Questions 

26. How is the sex of a newborn determined in humans?

Solution

The sex of the individual is determined by the genes inherited from parents. A new born who inherits an ‘X’ chromosome from father will be a girl and one who inherits a ‘Y’ chromosome will be a boy


27.  Do genetic combination of mothers play a significant role in determining the sex of a new born?

Solution

The genetic combination of mothers does not play a significant role in determining the sex of a new born, because mothers have a pair of X-chromosomes only. All children will inherit an ‘X’ chromosome from their mother regardless of whether they are boys or girls.


28. Mention three important features of fossils which help in the study of evolution.

Solution

The important features of fossils which help in the study of evolution are:

  1. Fossils represent modes of preservation of ancient species.
  2. The evolutionary traits among organisms and their ancestors can be established with the help of fossils.
  3. The time period in which the organisms lived can also be established with the help of fossils.


29. Why do all the gametes formed in human females have an X chromosome?
Solution
Human females have two X chromosomes known as the sex chromosomes. During meiosis at the time of gamete formation, one X chromosome enters each gamete. Hence all the gametes possess an X chromosome.

30. In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.
Solution
The type of sex chromosome contributed by the male gamete determines the sex of the infant. As the ratio of male gametes having X chromosome and those having Y chromosome is 50:50, the statistical probability of an infant to be a male or female is also 50 : 50..

31. A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Solution
Fewer number of individuals in a species impose extensive inbreeding among themselves. This in turn limits the variations and puts the species at a disadvantage if there are changes in the environment. The individuals fail to cope up with the environmental changes, and therefore they may become extinct

32. What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Solution
Homologous structures are the structures which have a common basic structure but perform different functions. For example, the fore limbs of reptiles, amphibians and mammals. Yes, homologous structures have a common ancestor but they are variously modified to carry out different activities.

33. Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Solution
Animals have a vast diversity in structures but they probably do not have a common ancestry. This is because common ancestry greatly limits the extent of diversity. Many of these diverse animals are inhabiting the same habitat, their evolution by geographical isolation and speciation is also not likely. Therefore, a common ancestry for all the animals is not the likely theory.

34. Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive 
(i) yellow seed 
(ii) round seed
Solution
(i) yellow — dominant green — recessive
(ii) round — dominant wrinkled — recessive

35. Why did Mendel choose pea plant for his experiments?
Solution
Mendel choose pea plant for his experiments for the following reasons
  • Pea plants are easy to grow 
  • They have short life span  
  • They got larger size flower  
  • Pea plants are self-pollinated

36. A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
Solution
A woman has only daughter; it means that the egg always received X chromosome from the sperm. If the sperm donates X chromosomes then the resultant child will be female and if the sperm donates Y chromosome then the baby will be a male.

Long Answer Questions 


37. Does geographical isolation of individuals of a species lead to formation of a new species? Provide a suitable explanation.
Solution
Geographical isolation gradually leads to genetic drift. As geographical isolation may impose limitations to sexual reproduction of the separated population. Slowly the separated individuals will reproduce among themselves and generate new variations. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

38. 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.
Solution
It is a debatable issue. If the appearance of complexity is concurrent with evolution then, human beings are certainly more evolved than bacteria. But if the totality of life characteristics is taken into account, then it will be hard to label either organism as evolved.

39.  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.
Solution
All human races have evolved from the common ancestry but they appear to be different.
Following are the evidence to support this view.
  • Similar size of brain.
  • Bipedal locomotion.
  • Same body design.
  • Hair on the body.
  • Ability to handle tools.
  • Ability to communicate using language.
  • Highly complex social behaviour.

40. Differentiate between inherited and acquired characters. Give one example for each type.

Solution
 

Inherited Characters

Acquired Characters

Characters that are passes on from parents to offspring

Characters appearing in an individual’s life time but cannot be transmitted to next generation

Alters Genotype and Phenotype

Alters Phenotype only

Transmitted to further generation

Cannot be transmitted to further generation

Results in genetic recombination

Results in response to environmental changes

Ex : colour of seeds, colour of eyes.

Ex : obese body, loss of a finger in an accident.


41. Give reasons why acquired characters are not inherited.
Solution
Acquired characters are the results of our body’s response to external stimuli such as food, disease, climate change. This results in a development of particular trait where change of phenotype is observed. But for characters to get inherited to generation Genotype of an organism should be changed. Acquired characters do not produce any change in the DNA of germ cells, so they cannot be inherited. Only those characters which have a gene for themselves can be inherited.

42. Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.
Solution
The living world shows immense diversity in size, form, structure and morphological features. But at the molecular level the various types of organisms exhibit unbelievable similarities. For instance, the basic biomolecules like DNA, RNA, carbohydrates, proteins etc. exhibit remarkable similarities in all living organisms.

43. In the following crosses write the characteristics of the progeny. 
 

Cross

Progeny

(a) RR YY x RR YY

Round, yellow Round, yellow

 ……………

(b) Rr Yy x Rr Yy
Round, yellow Round, yellow

……………

(c) rr yy x rr yy
wrinkled, green wrinkled, green

……………

(d) RR YY x rr yy
Round, yellow wrinkled green

…………….

Solution

Cross

Progeny

(a) RR YY x RR YY

Round, yellow Round, yellow

Round, Yellow 

(b) Rr Yy x Rr Yy
Round, yellow Round, yellow

Round, Yellow
Round, green
Wrinkled, yellow 
Wrinkled, green 

(c) rr yy x rr yy
wrinkled, green wrinkled, green

Wrinkled, green 

(d) RR YY x rr yy
Round, yellow wrinkled green

Round, yellow 



44. Study the following cross and showing self pollination in F1 , fill in the blank and answer the question that follows:

Parents

RRYY
Round, yellow

x

rryy
wrinkled green

F1 −

Rr Yy
Round, yellow

x

?

Solution
RrYy - Round yellow

45. In question 44, what are the combinations of character in the F2 progeny? What are their ratios?
Solution
rryy
(i) Round yellow — 9
(ii) Round green — 3
(iii) Wrinkled yellow — 3
(iv) Wrinkled green — 1
9 : 3 : 3 : 1 

46. Give the basic features of the mechanism of inheritance. 
Solution
The basic features of mechanism of inheritance are as follows:
  1. Genes control the characters.
  2. Each gene controls one character.
  3. There may be two or more forms of the genes.
  4. One form may be dominant over the other.
  5. Chromosomes carry genes.
  6. An individual has two forms of the gene which can be similar or dissimilar.
  7. At the time of zygote formation, the two forms separate.
  8. The two forms are brought together in the zygote

47. Give reasons for the appearance of new combinations of characters in the F1  progeny.
Solution
F1 plants have round and yellow seeds. Cross between generations can give rise to new combinations in F2 generation with round-yellow, round green, wrinkled yellow and wrinkled green in the ratio of  9 : 3 : 3 : 1.

Thus the chances for the pea seed to be round or wrinkled does not depend on the chances to be yellow or green. Therefore each pair of alleles is independent of the other pair. This is called as independent assortment.

NCERT Exemplar Chapter 9 Heredity and Evolution Class 10 Science Solutions

NCERT Exemplar Class 10 Science Chapter 9 Heredity and Evolution Solutions

NCERT Exemplar Solutions for Class 10 Science Chapter 9 Heredity and Evolution covers all the important questions and answers as well as advanced level questions. It helps in learning about the Accumulation of variation during reproduction, DNA copying, Heredity, Evolution, Speciation and geographical isolation.

The NCERT Exemplar solutions for class 10 science is very important for board exams. NCERT Exemplar Solutions for Class 10 Science Chapter 9 Heredity and Evolution is provided by our experts. They prepared the best solutions which help the students in understanding the solutions in an easy way. This chapters also covers the other topics like Evolution and classification, Fossils, Inherited traits, variations, stages of evolution and variation in generations.


Chapter Name

Chapter 9 Heredity and Evolution

Book Title

NCERT Exemplar for Class 10 Science

Related Study

  • NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution
  • Revision Notes for Class 10 Science Chapter 9 Heredity and Evolution
  • MCQ for Class 10 Science Chapter 9 Heredity and Evolution
  • Important Questions for Class 10 Science Chapter 9 Heredity and Evolution

Topics Covered

  • MCQ
  • Short Answers Questions
  • Long Answers Questions

NCERT Exemplar Solutions for Chapter 9 Heredity and Evolution Class 10 Science

Multiple Choice Questions

1. Exchange of genetic material takes place in
(a) vegetative reproduction
(b) asexual reproduction
(c) sexual reproduction
(d) budding

Solution
(c) Sexual reproduction

Apart from sexual reproduction other options are type of asexual reproduction where only single parent is involved. Hence exchange of genetic material takes place in sexual mode of reproduction.


2. 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 fertilisation
(b) self pollination
(c) cross fertilisation
(d) no fertilization

Solution
(c) cross fertilisation


3. 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’. 

Solution
(a) tallness is the dominant trait

Only dominant characters are expressed in first progeny in monohybrid cross.


4. 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

Solution
(d) For every molecule of fat there is a gene

Fats are not controlled by genes but every protein enzymes and hormones are controlled by specific gene.


5. If a round, green seeded pea plant (RR yy) is crossed with wrinkled, yellow seeded pea plant, (rr YY) the seeds produced in F1 generation are
(a) round and yellow
(b) round and green
(c) wrinkled and green
(d) wrinkled and yellow

Solution
(a) round and yellow

As round and yellow are the dominant characters in F1 generation, all the seeds will be round and yellow.


6. In human males all the chromosomes are paired perfectly except one. This/these unpaired chromosome is/are
(i) large chromosome
(ii) small chromosome
(iii) Y-chromosome
(iv) X-chromosome 

(a) (i) and (ii)
(b) (iii) only
(c) (iii) and (iv)
(d) (ii) and (iv)

Solution
(c) (iii) and (iv)

These are sex chromosomes that are not paired perfectly due to half size of Y chromosom.


7. 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

Solution
(b) the Y chromosome in zygote

The zygote develops into a male child if sperm with Y chromosome fertilize the egg. If sperm with X chromosome fertilize the egg zygote will develop into female child.


8. 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

Solution
(b) girl

If sperm with Y chromosome fertilize the egg zygote will develop into male child. If sperm with X chromosome fertilize the egg zygote will develop into female child.


9.  Select the incorrect statement
(a) Frequency of certain genes in a population change over several generations resulting in evolution
(b) Reduction in weight of the organism due to starvation is genetically controlled
(c) Low weight parents can have heavy weight progeny
(d) Traits which are not inherited over generations do not cause evolution

Solution
(b) Reduction in weight of the organism due to starvation is genetically controlled

Weight loss and gain are controlled by external factors.


10. New species may be formed if
(i) DNA undergoes significant changes in germ cells
(ii) chromosome number changes in the gamete
(iii) there is no change in the genetic material
(iv) mating does not take place

(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii), (iii) and (iv)
(d) (i), (ii) and (iii)

Solution
(a) (i) and (ii)

Without change and variation the genetic material, evolution cannot take place.


11. Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce F1 progeny that have round, yellow (RrYy) seeds. When F1 plants are selfed, the F2 progeny will have new combination of characters. Choose the new combination from the following (i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green 

(a) (i) and (ii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (i) and (iii)

Solution
(c) (ii) and (iii)


12. A basket of vegetables contains carrot, potato, radish and tomato. Which of them represent the correct homologous structures?
(a) Carrot and potato
(b) Carrot and tomato
(c) Radish and carrot
(d) Radish and potato

Solution
(c) Radish and carrot

They both have similar structure and they both growth beneath the earth.


13. Select the correct statement
(a) Tendril of a pea plant and phylloclade of Opuntia are homologous
(b) Tendril of a pea plant and phylloclade of Opuntia are analogous
(c) Wings of birds and limbs of lizards are analogous
(d) Wings of birds and wings of bat are homologous

Solution
(a) Tendril of a pea plant and phylloclade of Opuntia are homologous

Because of similar design and origin, tendril of a pea plant and phylloclade of opuntia are homologous.


14. If the fossil of an organism is found in the deeper layers of earth, then we can predict that
(a) the extinction of organism has occurred recently
(b) the extinction of organism has occurred thousands of years ago
(c) the fossil position in the layers of earth is not related to its time of extinction
(d) time of extinction cannot be determined

Solution
(b) the extinction of organism has occurred thousands of years ago
Older fossils are found deep in the earth.

15. Which of the following statements is not true with respect to variation?
(a) All variations in a species have equal chance of survival
(b) Change in genetic composition results in variation
(c) Selection of variants by environmental factors forms the basis of evolutionary processes.
(d) Variation is minimum in asexual reproduction

Solution
(a) All variations in a species have equal chance of survival

Only the useful variations have chances of survival. Nature choose the fittest variation to survive.


16. A trait in an organism is influenced by
(a) paternal DNA only
(b) maternal DNA only
(c) both maternal and paternal DNA
(d) neither by paternal nor by maternal DNA

Solution
(c) both maternal and paternal DNA

As the DNA is contributed to an offspring by both the parents, the traits are contributed by both the parents.


17. Select the group which shares maximum number of common characters
(a) two individuals of a species
(b) two species of a genus
(c) two genera of a family
(d) two genera of two families

Solution
(a) two individuals of a species

Species is the lowest taxon hence members of same species share maximum number of common characteristics.


18. According to the evolutionary theory, formation of a new species is generally due to
(a) sudden creation by nature
(b) accumulation of variations over several generations
(c) clones formed during asexual reproduction
(d) movement of individuals from one habitat to another

Solution
(b) accumulation of variations over several generations

Variation in the DNA for several generations leads to the formation of new species. No gamete formation takes place in asexual reproduction, hence it will not result in variations. Movement of individuals from one habitat to another will not affect DNA change.


19. From the list given below, select the character which can be acquired but not inherited
(a) colour of eye
(b) colour of skin
(c) size of body
(d) nature of hair

Solution
(c) size of body

The nature of the body is decides by a person’s food. Regular exercise helps in building muscular body. The size of the body is not inherited as body nature is not transferred to offsprings.


20. The two versions of a trait (character) which are brought in by the male and female gametes are situated on
(a) copies of the same chromosome
(b) two different chromosomes
(c) sex chromosomes
(d) any chromosome

Solution
(b) two different chromosomes

This is the reason why one progeny expresses one version and other versions is expressed in another progeny.


21. Select the statements that describe characteristics of genes
(i) genes are specific sequence of bases in a DNA molecule
(ii) a gene does not code for proteins
(iii) in individuals of a given species, a specific gene is located on a particular chromosome
(iv) each chromosome has only one gene 

(a) (i) and (ii)
(b) (i) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)

Solution
(b) (i) and (iii)

Statement ii) is wrong because genes code for specific proteins. Statement 4 is wrong because chromosomes have many number of genes.


22. In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F2 is
(a) 1 : 3
(b) 3 : 1
(c) 1 : 1
(d) 2 : 1

Solution
(b) 3 : 1

The following genotypes would be produced if a cross between pure tall plant (TT) and short plant (tt) is made:
TT(Pure tall), tt( Pure short) andTt ( Mixed tall).
This makes the ratio between tall and short plants is 3:1.


23. The number of pair (s) of sex chromosomes in the zygote of humans is
(a) one
(b) two
(c) three
(d) four

Solution
(a) one

The sex of the offspring is determined by the 23rd pair of chromosome, hence it is called as sex chromosome.


24.  The theory of evolution of species by natural selection was given by
(a) Mendel
(b) Darwin
(c) Morgan
(d) Lamarck

Solution
(b) Darwin

Mendel proposed laws of heredity. Morgan discovered mutation in drosophila. Lamarck proposed use and disuse theory.


25. Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution this means that
(a) reptiles have evolved from birds
(b) there is no evolutionary connection between reptiles and birds
(c) feathers are homologous structures in both the organisms
(d) birds have evolved from reptiles

Solution
(a) reptiles have evolved from birds

Dinosaurs had feathers but they could not fly. Later birds adapted the feathers for flight. As, dinosaurs were reptiles, this means that birds have evolved from them.


Short Answer Questions 

26. How is the sex of a newborn determined in humans?

Solution

The sex of the individual is determined by the genes inherited from parents. A new born who inherits an ‘X’ chromosome from father will be a girl and one who inherits a ‘Y’ chromosome will be a boy


27.  Do genetic combination of mothers play a significant role in determining the sex of a new born?

Solution

The genetic combination of mothers does not play a significant role in determining the sex of a new born, because mothers have a pair of X-chromosomes only. All children will inherit an ‘X’ chromosome from their mother regardless of whether they are boys or girls.


28. Mention three important features of fossils which help in the study of evolution.

Solution

The important features of fossils which help in the study of evolution are:

  1. Fossils represent modes of preservation of ancient species.
  2. The evolutionary traits among organisms and their ancestors can be established with the help of fossils.
  3. The time period in which the organisms lived can also be established with the help of fossils.


29. Why do all the gametes formed in human females have an X chromosome?
Solution
Human females have two X chromosomes known as the sex chromosomes. During meiosis at the time of gamete formation, one X chromosome enters each gamete. Hence all the gametes possess an X chromosome.

30. In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.
Solution
The type of sex chromosome contributed by the male gamete determines the sex of the infant. As the ratio of male gametes having X chromosome and those having Y chromosome is 50:50, the statistical probability of an infant to be a male or female is also 50 : 50..

31. A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Solution
Fewer number of individuals in a species impose extensive inbreeding among themselves. This in turn limits the variations and puts the species at a disadvantage if there are changes in the environment. The individuals fail to cope up with the environmental changes, and therefore they may become extinct

32. What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Solution
Homologous structures are the structures which have a common basic structure but perform different functions. For example, the fore limbs of reptiles, amphibians and mammals. Yes, homologous structures have a common ancestor but they are variously modified to carry out different activities.

33. Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Solution
Animals have a vast diversity in structures but they probably do not have a common ancestry. This is because common ancestry greatly limits the extent of diversity. Many of these diverse animals are inhabiting the same habitat, their evolution by geographical isolation and speciation is also not likely. Therefore, a common ancestry for all the animals is not the likely theory.

34. Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive 
(i) yellow seed 
(ii) round seed
Solution
(i) yellow — dominant green — recessive
(ii) round — dominant wrinkled — recessive

35. Why did Mendel choose pea plant for his experiments?
Solution
Mendel choose pea plant for his experiments for the following reasons
  • Pea plants are easy to grow 
  • They have short life span  
  • They got larger size flower  
  • Pea plants are self-pollinated

36. A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
Solution
A woman has only daughter; it means that the egg always received X chromosome from the sperm. If the sperm donates X chromosomes then the resultant child will be female and if the sperm donates Y chromosome then the baby will be a male.

Long Answer Questions 


37. Does geographical isolation of individuals of a species lead to formation of a new species? Provide a suitable explanation.
Solution
Geographical isolation gradually leads to genetic drift. As geographical isolation may impose limitations to sexual reproduction of the separated population. Slowly the separated individuals will reproduce among themselves and generate new variations. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

38. 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.
Solution
It is a debatable issue. If the appearance of complexity is concurrent with evolution then, human beings are certainly more evolved than bacteria. But if the totality of life characteristics is taken into account, then it will be hard to label either organism as evolved.

39.  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.
Solution
All human races have evolved from the common ancestry but they appear to be different.
Following are the evidence to support this view.
  • Similar size of brain.
  • Bipedal locomotion.
  • Same body design.
  • Hair on the body.
  • Ability to handle tools.
  • Ability to communicate using language.
  • Highly complex social behaviour.

40. Differentiate between inherited and acquired characters. Give one example for each type.

Solution
 

Inherited Characters

Acquired Characters

Characters that are passes on from parents to offspring

Characters appearing in an individual’s life time but cannot be transmitted to next generation

Alters Genotype and Phenotype

Alters Phenotype only

Transmitted to further generation

Cannot be transmitted to further generation

Results in genetic recombination

Results in response to environmental changes

Ex : colour of seeds, colour of eyes.

Ex : obese body, loss of a finger in an accident.


41. Give reasons why acquired characters are not inherited.
Solution
Acquired characters are the results of our body’s response to external stimuli such as food, disease, climate change. This results in a development of particular trait where change of phenotype is observed. But for characters to get inherited to generation Genotype of an organism should be changed. Acquired characters do not produce any change in the DNA of germ cells, so they cannot be inherited. Only those characters which have a gene for themselves can be inherited.

42. Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.
Solution
The living world shows immense diversity in size, form, structure and morphological features. But at the molecular level the various types of organisms exhibit unbelievable similarities. For instance, the basic biomolecules like DNA, RNA, carbohydrates, proteins etc. exhibit remarkable similarities in all living organisms.

43. In the following crosses write the characteristics of the progeny. 
 

Cross

Progeny

(a) RR YY x RR YY

Round, yellow Round, yellow

 ……………

(b) Rr Yy x Rr Yy
Round, yellow Round, yellow

……………

(c) rr yy x rr yy
wrinkled, green wrinkled, green

……………

(d) RR YY x rr yy
Round, yellow wrinkled green

…………….

Solution

Cross

Progeny

(a) RR YY x RR YY

Round, yellow Round, yellow

Round, Yellow 

(b) Rr Yy x Rr Yy
Round, yellow Round, yellow

Round, Yellow
Round, green
Wrinkled, yellow 
Wrinkled, green 

(c) rr yy x rr yy
wrinkled, green wrinkled, green

Wrinkled, green 

(d) RR YY x rr yy
Round, yellow wrinkled green

Round, yellow 



44. Study the following cross and showing self pollination in F1 , fill in the blank and answer the question that follows:

Parents

RRYY
Round, yellow

x

rryy
wrinkled green

F1 −

Rr Yy
Round, yellow

x

?

Solution
RrYy - Round yellow

45. In question 44, what are the combinations of character in the F2 progeny? What are their ratios?
Solution
rryy
(i) Round yellow — 9
(ii) Round green — 3
(iii) Wrinkled yellow — 3
(iv) Wrinkled green — 1
9 : 3 : 3 : 1 

46. Give the basic features of the mechanism of inheritance. 
Solution
The basic features of mechanism of inheritance are as follows:
  1. Genes control the characters.
  2. Each gene controls one character.
  3. There may be two or more forms of the genes.
  4. One form may be dominant over the other.
  5. Chromosomes carry genes.
  6. An individual has two forms of the gene which can be similar or dissimilar.
  7. At the time of zygote formation, the two forms separate.
  8. The two forms are brought together in the zygote

47. Give reasons for the appearance of new combinations of characters in the F1  progeny.
Solution
F1 plants have round and yellow seeds. Cross between generations can give rise to new combinations in F2 generation with round-yellow, round green, wrinkled yellow and wrinkled green in the ratio of  9 : 3 : 3 : 1.

Thus the chances for the pea seed to be round or wrinkled does not depend on the chances to be yellow or green. Therefore each pair of alleles is independent of the other pair. This is called as independent assortment.

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