Practice questions: Principle of Inheritance and Variation

The following are practice questions for Chapter-5 of Class-XII Biology:-“Principle of Inheritance and Variation”. These questions are sourced from previous years board examinations question papers, sample papers issued by CBSE, NCERT exemplar and certain other sources.

Part-1

1. What percentage of gametes produced by an individual with genotype AaBb will be ab?
2. Name the law that explains the expression of only one of the parental characters in the F1 generation of a monohybrid cross.
3. How many phenotypes of human skin colour are possible if two individuals of intermediate skin colour (AaBbCc) marry?
4. How many types of glycoproteins that determine the ABO blood group are found on the surface of RBCs in humans?
5. You have read that a single gene controls starch synthesis or size of the starch grains and the seed shape in pea plant. What is the phenotype produced by the genotype Bb? Why?
6. Not all character show true dominance. What are the two other possible types of dominance? Give an example of each.
7. Why did Mendel choose pea plant for his experiments?
8. Explain the law of dominance with the help of a cross.
9. Why did Mendel’s work remain unrecognised from 1865-1900? Who rediscovered his work?
10. In shorthorn cattle, coat colour may be red, white or roan.Roan is an intermediate phenotype expressed as a mixture of red and white hair. The following data were obtained from various crosses:
    red Χ red → all red
    white Χ white → all white
    red Χ white → all roan
    roan Χ roan → 1/4 red: 1/2 roan: 1/4 white
    1. what is the inheritance pattern for coat colour is shown in shouthon cattle?
    2. What are the genotypes of parents and offspring of each cross?
11. A test is performed to know whether the given plant is homozygous dominant or heterozygous. Name the test and phenotypic ratio of this test for a monohybrid cross.
12. Can a child have blood group O if his parents have blood group ‘A’ and ‘B’? Explain.
13. Some of the characters in humans exhibit multiple allelism. Yet, these characters are controlled by two alleles only. Justify.
14. Differentiate between dominant and co-dominant.
15. In Mendel’s breeding experiment on garden pea, the offspring of F2 generation are obtained in the ratio of 25% pure yellow pod, 50% hybrid green pods and 25% green pods State
    1. which pod colour is dominant
    2. The Phenotypes of the individuals of F1 generation.
    3. Workout the cross
16. A dihybrid heterozygous round, yellow-seeded garden pea (Pisum sativum) was crossed with a double recessive plant.
    1. What type of cross is this?
    2. Work out the genotype and phenotype of the progeny.
    3. What principle of Mendel is illustrated through the result of this cross?
17. In Pisum sativum tallness is dominant over dwarfness and yellow seeds are dominant over green. Work out a dihybrid cross for the above condition starting with P1 generation. Also, mention the genotypic and phenotypic ratio.
18. A particular garden pea plant produces only violet flowers. It may or may not be homozygous dominant for the trait. How would you ensure the genotype? Explain with crosses.
19. Define polygenic inheritance? Explain the concept with the help of an example.
20. What do you understand by the concept of pleiotropy? Explain the concept with the help of one condition observed in plants and humans.

Part-2

VSA Type-I  [1 Mark]

1. Name the phenomenon and the cell responsible for the development of drones in honeybees.
2. Name one autosomal dominant and one autosomal recessive Mendelian disorders in human beings.
3. Name the respective pattern of inheritance where F1 phenotype.
   1. Does not resemble either of the two parents and is in between the two.
   2. Resemble only one of the two parents.
4. Why, in test cross, did Mendel cross a tall pea plant with a dwarf pea plant only?
5. In a dihybrid cross, when would the proportion of parental gene combinations be much higher than non-parental types, as experimentally shown by Morgan and his group.
6. With the help of one example of each, provide a genetic explanation for the following observations:
   1. F1 generation resembles both the parents.
   2. F1 generation does not resemble either of the parents.

VSA Type-II  [2 Mark]

1. Differentiate between multiple alleles and polygenes.
2. Bring out the differences between pleiotropy and multiple allelism, with an example for each.
3. How does a test cross help in identifying the genotype of the organism? Explain.

SA Type [3 Mark]

1. Who proposed the chromosomal theory of inheritance? Point out any two similarities between the behaviour of genes and that of a chromosome.
2. In a breeding experiment, a phenotypic ratio of 3:3:3:1 was obtained on crossing a pea plant with green, inflated pods with another pea plant bearing green constricted pods. Write the genotypes of the parents and judge the accuracy of the result, using a punnet square.
3. 1. Sickle cell anaemia in humans is a result of point mutation. Explain.
   2. write the genotype of the normal parents who have produced a sickle cell anaemia offspring.
4. A non-haemophilic couple was informed by their doctor, there is a possibility of a haemophilic child to be born to them. Explain the basis on which the doctor conveyed the information. Give the genotypes and phenotypes of all the possible children who could be born to them.
5. Persons with Down’s syndrome and those with Klinefelter’s syndrome have 47 chromosomes each, but they show many differences. Explain why?
6. Study the pedigree chart showing the pattern of blood group inheritance in a family.
   
   1. Give the genotype of the following:
      1. Parents
      2. The individual X in the 2^nd generation.
   2. State the possible blood groups of the individual ‘Y’ in the third generation.
   3. How does the inheritance of this blood group explain codominance?
7. Explain the mechanism of sex determination in insects like Drosophila and grasshopper.
8. Explain in brief the three different types of thalassaemia.

LA Type [5 Mark]

1. 1. A character may or may not be expressed, but they are inherited by every generation. Justify.
   2. Study the given pedigree chart and answer the questions that follow.

   

   1. 1. Is the trait sex-linked or autosomal dominant or autosomal recessive?
      2. Write the genotypes of parents in generation I.
      3. Give the genotype of the first child in generation II and that of the first and second child in generation-III.
2. 1. A cross between two pink-flowered Snapdragon plants yielded a progeny with red, pink and white-flowered plants. Explain the pattern of inheritance and the phenomenon involved in it. Mention the phenotypic and genotypic ratios in the progeny.
   2. Give four as to why Drosophila is well suited for lab experiments in genetics.
3. A true-breeding pea plant homozygous for axial, violet flower is crossed with another pea plant with the terminal, white flower.
   1. What would be the phenotype and genotype of F1 and F2 generations?
   2. Give the phenotypic ratio of F2 generation.
   3. List Mendel’s generalisation that can be derived from the above cross.
4. Write the symptoms of haemophilia and sickle cell anaemia in humans. Explain how the inheritance pattern of the two disease differs from each other.

Practice-questions based On NCERT Exemplar

Very Short Answer Type 

1. Do you think Mendel’s laws of inheritance would have been different if the characters that he chose were located on the same chromosome?
2. Enlist the steps of controlled cross-pollination. Would emasculation be needed in a cucurbit plant? Give reasons for your answer.
3. The pedigree chart given below shows a particular trait which is absent in parents but present in the next generation  irrespective of  sexes. Draw your conclusion on the basis of the pedigree.

4. In order to obtain the F1 generation, Mendel pollinated a pure-breeding tall plant with a pure breeding dwarf plant. But for getting the F2 generation, he simply self-pollinated the tall F1 plants. Why?
5. For the expression of traits,genes  provide only the potentiality and the environment provides the opportunity. Comment on the veracity of the statement.
6. How does a mutagen induce mutation? Explain with example.

Short answer type

7. In a Mendelian monohybrid cross, the F2 generation shows identical genotypic and phenotypic ratios. What does it tell us about the nature of alleles involved? Justify your answer.
8. Why is it that the chances of having a child with Down’s syndrome increase if the age of the mother exceeds forty years?
9. A plant with red flowers was crossed with another plant with yellow flowers. If F1 showed all flowers orange in colour, explain the inheritance.
10. Why is the frequency of red green colour blindness is many times higher in males than that in the females?
11. It is said, that the harmful alleles get eliminated from the population over a period of time, yet sickle cell anaemia is persisting in the human population. Why?
12. Discuss the contributions of Morgan and Sturvant in the area of genetics.