(b) : Establishment of sex through differential development in an individual at an early stage of life is called sex determination. It is determined at the time of fertilization and is also called as syngametic sex determination. The female is homomorphic (isomorphic) possessing two similar sex chromosomes, $XX$ and the male is heteromorphic possessing one $X$ chromosome similar to that of female and one shorter and morphologically different $Y$ chromosome. The female is said to be homogametic (produces similar eggs) and the male heterogametic (produces two types of sperms $i.e.$, $X$ or $Y$). Sex is determined at the time of fertilization by the kind of sperm ($X$ or $Y$) that fuses with the ovum $(X)$.