According to this system female is homogametic or XX and male is heterogametic or XY. Females produce one type of egg (X) and males produce two types of sperm (X and Y). When a woman’s egg X meets a man’s sperm X, a female child (XX) will be produced. Again, the union of the woman’s egg X with the man’s sperm Y will produce a son (XY). This method determines the sex of animals such as humans, Drosophila, various insects, cannabis, cockroaches, Elodea etc.