Sex linkage: a geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) is said to be sex-linked if it maps to a sex chromosomeplugin-autotooltip__default plugin-autotooltip_bigSex chromosomes: in some species, these are a set of chromosomes that determine sex. In some species, females are homogametic (XX) and males are heterogametic (XY), whereas in other species it is the other way around (homogametic ZZ males and heterogametic ZW females). Not all species use sex.