Sex-Determination Systems
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Sex-determination systems assign sex chromosomally: humans and most mammals use XY, some insects use XO, and birds and butterflies use ZW.
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Human XY males are the heterogametic sex, while ZW birds reverse this — females, not males, carry the two different sex chromosomes.
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Which chromosome type an organism inherits at fertilization is what Bio 1047's X-linked crosses assume, not derive.