BIOL207 Lecture Notes - Lecture 12: Nettie Stevens, Pseudoautosomal Region, Allosome
8 Oct 2013
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X/y = male (males have heterozygous genotype) Reverse of xy system: z/w = female (females have heterozygous genotype, z/z = male. It was discovered that beetles had mismatched chromosomes that pair up with eachother during meiosis i (discovered by nettie stevens: given the name x" and y" chromosomes. Millions of years ago, they were identical (homologous with eachother) Then y" chromosome lost most of its genes. The x" chromosome still has most though: also, sex chromosome have evolved many times: That why there is also a zw sex chromosome system. Sex determination in mammals: gonad differentiation relies on several genes. Dosage compensation in mammals: females have double x-linked genes than males, solution: decreased x-linked gene expressions in females. Only one of the x-chromosomes in females is active. Active one: behaves normally during interphase: unpackages itself. It still gets replicated though: xi turns into a barr body during interphase.
