Heredity and Variation

Heredity is the transmission of characteristics, physical or mental from parents to offspring that is, from one generation to the successive generation. It is of common knowledge that "Like produces like" - human beings give birth to babies, a cat gives birth to kittens and a hen produces chicks. Although offsprings resemble their parents, they are not identical to them. The reproductive processes give rise to new individuals that are similar, but subtly different. They exhibit a departure in some of the qualities from the previous generation.

These differences shown by the individuals of a species are termed as variations. Some amount of variation is always seen and these appear more pronounced for species that reproduce sexually, when compared to those having asexual reproduction. All the plants of wheat in a field seem one and the same at harvest time. But if you view a litter of puppies the variations are quite evident, especially as they grow. This is true of human beings also, who reproduce sexually. Quite distinct variations are visible among different individuals and even offsprings born to same parents are different. We shall study the transmission of hereditary characters and variations from one generation to the other.