- (biology) Having a male configuration of chromosomes as per the XY system.
- 1994, R. V. Short, E. Balaban (eds), The Differences between the Sexes, page 15, ISBN 052144411X.
- There is evidence to show that, occasionally, XY germ cells can undergo oogenesis when in an ovarian environment.
2009, Gerald N. Callahan, Between XX and XY: Intersexuality and the Myth of Two Sexes, ISBN 1556527853, page 30:
- The group at John Hopkins, as well as many others, dropped the "true sex" policy (such as XX or XY) and adopted the "optimal gender" policy for assigning sex to sexually ambiguous children.
- (biology) Synonym of