CBSE Class 12 Biology Sexual Principles of Inheritance And Variation Worksheet

Question. Polygenic genes show 
(a) similar genotype
(b) different phenotype
(c) different karyotype
(d) different genotype
Answer. B

Question. In Huntington’s disease, the unaffected persons are homozygous for normal allele h. The following is erroneous because

B-142 Topicwise AIIMS Solved Papers – BIOLOGY
(a) it shows both male and female affected by Huntingtons disease
(b) either person 6 or 7 should have the disease, if individual 11 shows the disease.
(c) at least one of the 2 children (8, 9) should have the disease
(d) all of these
Answer. B

Question. Discontinuous variations are 
(a) essential features
(b) acquired characters
(c) non-essential changes
(d) mutations
Answer. D

Question. Bird females have chromosome arrangement as
(a) XY
(b) XO
(c) WZ
(d) WW
Answer. C

Question. Gene pool is referred to 
(a) the genetic drift caused in a population
(b) aggregate of all genes and their alleles in a population.
(c) deletion of non essential genes.
(d) induce cell division
Answer. B

Question. Given below is a highly simplified representation of the human sex chromosomes from a karyotype.

The genes a and b could be of
(a) colour blindness and body height
(b) attached ear lobe and Rhesus blood group
(c) haemophilia and red-green colour blindness
(d) phenylketonuria and haemophilia
Answer. C

ASSERTION REASON QUESTIONS

Directions : These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following five responses.
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.
(e) If the Assertion is incorrect but the Reason is correct.

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 : Phenylketonuria is a recessive hereditary disease caused by body’s failure to oxidize an amino acid phenylalanine to tyrosine, because of a defective enzyme.
Reason : It results in the presence of phenylalanine acid in urine. 
Answer. B

Question. Assertion : In humans, the gamete contributed by the male determines whether the child produced will be male or female.
Reason : Sex in humans is a polygenic trait depending upon a cumulative effect of some genes on X-chromosome and some on Y-chromosome. 
Answer. C

Question. Assertion : Haemophilia is a recessive sex linked disease.
Reason : Haemophilia occurs due to mutation of a structural gene on chromosome 15
Answer. C

PRINCIPLES OF INHERITANCE AND VARIATION

 

1. Name one autosomal dominant and one autosomal recessive Mendelian disorder in humans.

 

2. Write the genotype of i) an individual who is carrier of sickle cell anaemia gene but apparently unaffected, and ii) an individual affected with the disease.

 

3. A human being suffering from Down’s syndrome shows trisomy of 21st chromosome. Mention the cause of this chromosomal abnormality.

 

4. Write the percentage of F2 homozygous and heterozygous populations in a typical monohybrid cross.

 

5. A man with blood group A married a woman with B group. They have a son with AB blood group and a daughter with blood group O. Workout the cross and show the possibility of such inheritance.

 

6. The male fruit fly and female fowl are heterogametic while the female fruit fly and male fowl are homogametic. Why are they called so?

 

7. A plant of Antirrhinum majus with red flowers was crossed with another plant of the same species with white flowers. The plants of the F1 generation bore pink flowers. Explain the pattern of inheritance with the help of a cross.

 

8. A woman with blood group ‘O’ married a man with AB group. Show the possible blood groups of the progeny. List the alleles involved in this inheritance.

 

9. How does a test cross help in identifying the genotype of the organism? Explain.

 

10. When a tall pea plant was selfed, it produced one fourth of its progeny as dwarf. Explain with the help of a cross.

 

11. i) Why are grasshopper and Drosophila said to show male heterogamety? Explain.

ii) Explain female heterogamety with the help of an example.

 

12. Explain the pattern of inheritance of haemophilia in humans. Why is the possibility of a human female becoming haemophilic extremely rare? Explain.

 

13. A non-haemophilic couple was informed by their doctor that there is possibility of a haemophilic child be born to them. Explain the basis on which the doctor conveyed this information. Give the genotypes and the phenotypes of all the possible children who could be born to them

 

14. Study the pedigree chart and answer the questions that follow:

 

a) Is the trait recessive or dominant?

b) Is the train sex- linked or autosomal?

c) Give the genotypes of the parents shown in generation I and their third child shown in generation II and the first grand child shown in generation III.

 

15. Haemophilia is a sex linked recessive disorder of humans. The pedigree chart given below shows the inheritance of haemophilia in one family. Study the pattern of inheritance and answer the questions given.

a) Give all the possible genotypes of the members 4,5 and 6 in the pedigree chart.

b) A blood test shows that the individual 14 is a carrier of haemophilia. The member numbered 15 has recently married the member numbered 14. What is the probability that their first child will be haemophilic male?

 

16. Inhertiance pattern of ABO blood groups in humans shows dominance, codominance and multiple allelism. Explain each concept with the help of blood group genotypes.

 

17. Who proposed chromosomal theory of inheritance? Point out any two similarities in the behaviour of chromosomes and genes.

 

18. Explain the sex determination mechanism in humans. How is it different in birds.

 

19. Explain the mechanism of sex determination in insects like Drosophila and grasshopper.