Table 1.

Sex chromosome types in vertebrates, insects and angiosperms

Taxonomic group	Number of species					Ratio
	XY	XO	ZW	ZO	Other1	XO/XY	ZO/ZW
Vertebrates	722	15	480	3	254	0.02	0.01
Insects	4415	1857	37	25	156	0.42	0.68
Angiosperms	23	0	1	0	19	0.00	0.00
Total	5160	1872	518	28	429	0.36	0.05

Data are based on the Tree of Sex database downloaded on Nov. 16, 2023.

¹Other includes species with complex sex chromosomes (e.g., more than one X or Z) and homomorphic sex chromosomes.