Pronunciation: (zī-gos'i-tē, zi-),[key] —n.Genetics. 1. the characterization of an individual's hereditary traits in terms of gene pairing in the zygote from which it developed. Cf. homozygous, heterozygous. 2. the characterization of twinning and multiple births in terms of the combination of alleles for particular hereditary traits. Cf. monozygotic, dizygotic.