BIOL 240 1st Edition Lecture 9Outline of Last Lecture I. Sex-linked GenesII. NondisjunctionOutline of Current Lecture I. Sex DeterminationII. Structure of Y chromosomeIII. Barr bodiesCurrent LectureI. Sex DeterminationEx: Worms…. Most are XX hermaphrodites (both ovaries and testes). Nondisjunction yields XO worms, which are male.- Can evolve from the standard XX or XY system by the deterioration of the Y chromosome- Terms:o Homogametic sex—2 identical sex chromosomes (XX); produces like gameteso Heterogametic sex—2 different sex chromosomes (XY) or (XO); produces different gameteso ZZ/ZW—in chickens, females are ZW and males are ZZII. Structure of Y chromosome1. Pseudoautosomal region (PAR)—homologous to X chromosome; located at tips; only region where synapsis occurs between X and Y2. Sex-determinging region (SRY)—produces protein TDF which is expressed at 6-8 weeks gestation and causes gonads to develop as testisSo, how do males get away with only having one X chromosome? After all,autosomal chromosomes exist in like pairs…III. Barr bodies- Female cells exhibit barr bodies, which are condensed DNA masses- Ohno proposed that they are inactivated X chromosomes- All extra X chromosomes are inactivatedThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Lyon hypothesis: X chromosome inactivation occurs randomly and inherited
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