heterogametic

Heterogametic refers to the sex of an organism that possesses two different sex chromosomes, resulting in two distinct types of gametes with respect to the sex chromosomes. In the XX/XY systems of most mammals, including humans, males are heterogametic (XY) and females are homogametic (XX). The term contrasts with homogametic, in which the sex chromosome complements are identical (XX in female mammals). In other taxonomic groups, such as birds, many reptiles, some insects, and some fish, the system is reversed: females are heterogametic (ZW) and males are homogametic (ZZ).

During meiosis, the heterogametic sex produces gametes carrying different sex chromosomes (X or Y in XY systems; Z or W in ZW systems), while the homogametic sex produces gametes with the same sex chromosome content (XX or ZZ).

The heterogametic status influences the inheritance of sex-linked genes. In XY species, X-linked traits may be expressed differently in males and females; Y-linked traits pass only from father to son. In ZW species, the pattern is inverted, with genes on the Z chromosome showing sex-specific inheritance and some genes effectively dosage-limited in the heterogametic sex.

Not all species use chromosomal sex determination; environmental factors such as temperature can determine sex in some reptiles and fish.

Understanding heterogamety helps explain patterns of sex-linked inheritance and the evolution of diverse sex-determination systems across the tree of life.