Question

explain the mechanism of hereditary changes

Answer 1

Definition of Heredity:

Under heredity we include all the factors that were present in the organism at birth. In other words, it is the sum-total of inborn individual tracts. Heredity has two aspects – biological and psychological. Biologically, it means the sum total of biological traits that are present in the fertilised ovum. Psychologically it means the traits, innate tendencies, and capacities that resemble between the parents and the child.

Mechanism of Heredity:

1. Mating:

Mating is the first step for reproduction. It is essential for the union of the male germ cell spermatozoa with the female ovum. The union causes fertilisation of the ovum. Growth and development takes place by the multiplication of the fertilized cell through continuous division (or mitosis).

2. Growth:

Growth involves repeated division of the fertilised cell or zygote.

3. Chromosomes:

The fertilised ovum consists of a semi-fluid mass called cytoplasm, and within that there is a small nucleus of denser material. The nucleus includes the elementary carriers of the traits of both the parents, called chromosomes. In a fertilised ovum, there are 24 pairs of chromosomes, 24 from father and 24 from mother.

4. Genes:

Each chromosome consists of small particles numbering 40 to 100, which are called genes. In fact the genes are the real carriers and determinants of heredity. Each gene carries some structure which is responsible for the development of a particular trait. There is experimental evidence to prove that the physical traits, like the colour of the eyes, the skin, the size, the type of blood, and some organic diseases are represented by respective genes.

5. Chance factor:

Both the ova and the sperm before fertilisation contains 24 pairs of chromosomes each. On fertilisation, there will be not 24 + 24 or 48 pairs, but only 24 pairs. Others drop out equally from both. Which 24 of 48 chromosomes of the sperm or the ova will continue, is a matter of chance. A mathematician will tell us that there are millions of permutations and combinations possible for the chromosomes. That is why no two persons can be identical.