Heterogametic sex (digametic sex) refers to the sex of a species in which the sex chromosomes are not the same. For example, in humans, males, with an X and a Y sex chromosome, would be referred to as the heterogametic sex, and females having two X sex chromosomes would be referred to as the homogametic sex.
However, in birds, and some reptiles, males have two Z sex chromosomes and so are the homogametic sex, while females, with one Z and one W chromosome, are the heterogametic sex. Platypus males are heterogametic while females are homogametic. Among the insects, Lepidopterans (butterflies and moths) have heterogametic females, but in Drosophila, males are the heterogametic sex.
Heterogamesis can lead to reduced or absent meiotic recombination between the sex chromosomes, and in some species this extends to the autosomes, a phenomenon called achiasmy. For example, most lineages of male Drosophila melanogaster flies are achiasmic, lacking recombination on all chromosomes, although females show recombination.
- Haldane's rule, concerns hybrid speciation
- Haldane-Huxley rule, concerns achiasmy
- XY sex-determination system
- ZW sex-determination system
- King R.C.; Stansfield W.D.; Mulligan P.K. (2006). A Dictionary of Genetics (7th ed.). Oxford. p. 204.
- James Franklin Crow; William F. Dove, eds. (2000). Perspectives on genetics: anecdotal, historical, and critical commentaries, 1987–1998. Madison, WI: University of Wisconsin Press. ISBN 978-0-299-16604-5.
- Lenormand, Thomas (February 2003). "The Evolution of Sex Dimorphism in Recombination". Genetics. 163 (2): 811–22. PMC 1462442. PMID 12618416.