Whenever an infant is born in a family, the relatives begin to wonder about the resemblance of the infant’s eyes, facial features, complexion, colour of hair with those of the parents, siblings and grand parents. The source of such resemblances and differences are in the genes that are passed down form parents to children and so on generation after generation. This inheritance of genes is termed heredity the study of reasons of heredity is Genetics.
New individuals develop features according to the genes inherited by them from their parents. The transmission of characters from one generation to the next, that is from parents to offsprings is known as heredity.
Siblings from same parents are unique and differ from each other except the identical twins. Such differences are termed variations. Variation means differences between parents and their offsprings or between offsprings of same parents or between members of the same population.
Variation in a population is very important. It has survival value for the population. This is because if the environment changes, some individuals (variants) may be able to adapt to new situations and save the population from dying out. Variation arises due to mutation or sudden change in the genes. Variation also arises because genes get shifted and exchanged during meiosis at the time of formation of gametes, giving rise to new gene combinations.
At fertilization, there is random mixing of paternal and maternal chromosomes with different gene combinations. Such a source of variation which is most common is called genetic recombination.
Heritable Variations generally arise because of mutation and recombination.