Homozygous and Weterozygous
In an individual two identical alleles may exist [or a given character and, hence, the individual is referred to as Homozygous (e.g. AA and aa). If there are two non-identical or different alleles for a given character, the indivitlual is reffered to as heterozygous (e.g. Aa).
Let us examine a situation where both the parents arc homozygous. The male is homozygous recessive aa, and female is homozygous dominant AA. During nlciosis in the male the two 'a' alleles separate from each other so lhat cach spcrln has only asingle 'a' allele. Similarly, in the female parent each egg has one 'A' allelc. 'I'hc fertilisation of the 'A' egg by 'a' sperm results in n hcterozygoiis atiimal with 'Aa'. The form of gene which occurs in an individual in nalure is called the 'wild type' while a 'mutant type' is the one in which the genetic material is somcwhat altered. Mutants arise due to various reasons.
The alleles which express themselves in both honiozygous and heterozygous conditions are known as the dominant alleles. For example, 1T represents tallricss (homoqgous). The individuals having the alleles TT, and Tt would be tall as T is a dominant allele and it can express itself in both homozygous and heterozygous conditions. Some alleles express themselves only in hornozygous condition ant1 arc rcfcrrcd to as recessive alleles. In the height characteristic, dwarfness can be seen in individuals that have the alleles 'tt', i.e., recessive allelus are expresscti in homozygous condition only.