May 20, 2010

Birds do it, differently.

People, like dogs and ginko trees, do it using the XY sex-determination system: The sperm determines the sex; individuals with a pair of the same sex chromosomes (XX), or "homogametes," are female, while individuals with a pair of different sex chromosomes (XY), or "heterogametes," are male.

Birds (& some fish, insects, & reptiles) do it differently: They use the ZW sex-determination system, in which the ovum determines the sex, males are homogametic (ZZ), and females are heterogametic (ZW).

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