Describe male heterogamety.

Explanation

In this mechanism, the female sex has two X chromosomes while the male sex his only a single X chromosome. The heterogametic male may be of the following two types.
1) XX-XO type: IN certain insects belonging to order Hemiptera (true bugs), Orthoptera (grass hoppers) and Dicytoptera (cockroaches), female has two X chromosomes (XX) and are thus homogametic, while male has only single X chromosome (XO). THe male being heterogametic sex produces two types of sperms, half with X chromosome and half without X chromosome in equal proportions. The sex of the offspring depends upon the sperm that fertilises the egg, each of which carries a single X chromosomes. THus fertilisation between male and female gametes always produced zygotes with one X chromosome from the female but only 50% of the zygotes have an additional X chromosome from the male. In this way XO and XX types would be formed in equal proportions, the former being males and the latter being females.

2) XX-XY type: In man, other mammals, certain insects incluing Drosophila, the females possess two X chromosomes (XX) and are thus homogametic, produce one kind eggs, each one with one X chromosome. While the males possess one X and one Y chromosome (XY) and are hence, heterogametic. They produce two kinds of sperms, half with X chromosome and half with Y chromosome. The sex of embryo depends on the kind of sperm. AN egg fertilised by a X bearing sperm, produces a female, but if fertilised by a Y-bearing sperm, a male is produced