NCERT Questions for Class 12 Biology Chapter 4 – Principles of Inheritance and Variation

Important Questions with Solutions of Class 12 Biology Chapter 4 – Principles of Inheritance and Variation

1) Distinguish between Turner’s syndrome & Klinefelter’s syndrome.

Ans – The differences between Turner’s syndrome & Klinefelter’s syndrome are:

Turner’s syndrome	Klinefelter’s syndrome
Female undergoes this syndrome.	Male undergoes this syndrome.
It consists of 45 chromosomes thus one X chromosome less.	It consists of 47 chromosomes thus one X chromosome more.

2) Why is hemophilia not hereditary from a father to his son?

Ans – X chromosome carries the gene of hemophilia. In the male, the X chromosome is derived from his mother and the Y chromosome from his father thus the male or the father can only transfer the X chromosome to his daughter, basically female offspring. Therefore, hemophilia is not hereditary from a father to his son.

3) Considering Mendel’s factor, there are two similarities between the behavior of genes during inheritance and chromosomes during cell division.

Ans – 2 common similarities within the behavior of genes during the time of inheritance and chromosomes during cell division are:

1. Chromosomes are bound in pairs like Mendelian factors in diploid cells.
2. During meiosis, the chromosomes of various homologous pairs are gathered independently into the gametes. It results in a random showing parallelism considering Mendelian factors.

4) The zygote emerged from an XX-egg fertilized by Y-carrying sperm resulting in certain abnormalities in a child. Explain. What is this abnormality called?

Ans – The zygote emerges from an XX-egg fertilized by Y-carrying sperm & causes Klinefelter syndrome in the child with an XXY genotype which follows into the development of prominent feminine characters in the child such as tall feminine physical structure, breast enlargement, brewing pubic hair, poor growth of beard and then comes sterility.

5) Explain the cause and symptoms (any four) of Klinefelter’s syndrome.

Ans – Klinefelter’s syndrome is caused by the extra chromosome in males i.e. XXY chromosome.

The symptoms found in the sufferers of Klinefelter’s syndrome are:

1. Enlargement of breasts.
2. Brewing pubic hair in a feminine pattern
3. Poor growth of beard.
4. Underdeveloped testes.
5. Tall feminine physical structure.

6) Define pedigree analysis and state its uses.

Ans – Pedigree analysis is studying the hierarchal patterns of a particular characteristic. It’s a vigorous push to track the inheritance of specific characteristics with any other existing abnormalities or diseases.

7) When a woman from an O blood group married to a man of an AB blood group.

1. Discuss all the possible phenotypes and genotypes of the offspring.
2. Elaborate the kind of dominance present between the parents and their offspring.

Ans – When a woman of an O blood group married to a man of an AB blood group.

1. The possible phenotypes of the offspring are blood group A and B and the possible genotypes are IAi & IBi along with this blood group AB has IA IB alleles & blood group O has ii alleles which further forms both types of blood group A and B while the genotype of the offspring will be IAi & IBi.

Father’s genes: IA IB

Mother’s genes: ii

Hence, the cross will be:

Mother’s genes → Father’s genes ↓	i	i
IA	IAi	IAi
IB	IBi	IBi

2. Considering the above case, the dominance between the parents and their offspring (IA & IB) is equally dominant or co-dominant. In multiple allelism, a gene I sustains in 3 allelic forms IA, IB & i.

Why is understanding inheritance and variation important?

Knowing the basis of inheritance and variation is important for a variety of reasons. For instance, it enables a detailed study and treatment of genetic diseases. Also it enables the selective breeding of plants and animals for desirable traits and it gives insights into the evolutionary process and the diversity of life on earth.

The basis of the theory of variation of inheritance is founded by the laws formulated by Gregor Mendel, the father of modern genetics. These are the law of dominance, the segregation law, and the law of independent assortment. Under the guidance of these laws, Mendel was in a position to unravel mysteries of characteristics from one generation to the next.

What kinds of characteristics are inherited?