In biology, it takes on two meanings: 1. heterogametic sex: the gender that has two different sex chromosomes (e.g., in humans, the male is heterogametic because he has an X and a Y chromosome, while in avian species , the female is heterogametic because she has a W and a Z chromosome); 2. homogametic sex: the gender that has two copies of the same sex chromosome (e.g., in humans, the female is homogametic because she is XX , while in birds, the male is homogametic because he is ZZ).
See Chromosome, Gender, Gender identity, Own-sex schema, Sex chromosomes, Sexually dimorphic, Sex ratio, Theory of sexual selection