Lyon hypothesis

noun
Ly·​on hypothesis | \ ˈlī-ən- How to pronounce Lyon hypothesis (audio) \

Medical Definition of Lyon hypothesis

: a hypothesis explaining why the phenotypic effect of the X chromosome is the same in the mammalian female which has two X chromosomes as it is in the male which has only one X chromosome: one of each two somatic X chromosomes in mammalian females is selected at random and inactivated early in embryonic development