Define heredity. Explain the mechanism of hereditary changes.
Answer:
Heredity is the transfer of genetic characters or traits from parents to their offsprings.
The traits that are transferred to the progeny are known as inherited traits.
Example eye colour, ear lobe structure, blood group.
Heredity includes not only physical but also physiological qualities. These qualities may be either expressed (if the trait is dominant) or they may be latent in the offspring (if the trait is recessive).
The mechanism of heredity involves:
- Mating: Fusion of the male germ cell spermatozoa with the female ovum (tranfer of gametes and their fusion)
- Growth: Repeated mitotic division of the zygote (fertilised egg).
- Chromosomes: Both the male and female gametes contain nucleus which further contains the chromosomes. Both of them have 24 chromosomes each. (Therefore, called haploid cells)
- Gene: Chromosomes further contain smaller structures that are called genes. Now these genes are the structures that get passed on. Different genes are responsible for different characters. For example, there are genes that determine eye colour, genes that determine your blood group etc. Genes get passed onto the progeny from both the mother and father. Depending on the dominance of the gene, that particular character would be expressed in the progeny.
- Chance factor: Even though each parent passes on 24 pairs of chromosomes to the progeny, the progeny doesn't have 48 pairs of chromosomes on fertilization. Due to reduction divison (meiosis) there are 24 pairs of chromosomes only. Which 24 pairs will be selected is a matter of chance and is not predetermined.