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Sex determination.docx

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Michelle French

Sex determination October-27-12 5:55 PM Somatic cells contain 46 chromosomes • Meiosis reduces number to 23 chromosomes At 6 weeks the fetus has bipotential primordium and rudimentary male and female reproductive tracts • Female ovary o Mullerian duct -> Fallopian tube, uterus, upper vagina • Male testis o Wolffian duct -> epididymis, vas deferens, seminal vesicle Y chromosome has SRY gene that promotes testes development • Altered y chromosome lacks SRY gene • Codes for a gene regulatory protein (transcription factor Function: • SRY gene -> SRY -> SOX9 gene (negatively regulates SRY gene) -> SOX9 (positively regulates SOX9 gene) -> transcription of many genes -> development of sertoli cells and testes, expression of anti-mullerian hormone • SOX9 initiates sertoli cell differentiaton o Proliferation of sertoli precursors o Sertoli precursors organize around clusters of germ cells • Cellular events downstream of SOX9 rapidly organize testis structure o Bipotential gonad ->SRY -> sertoli cell differentiator • Proliferation • Migration • Organization • Vascularization • leydig cell differentiation Hormones regulate sex differentiation • Sex determining region of Y chromosome in embryonic germ cells (SRY gene) • Produces testis determining SRY protein • Initiates production of multiple proteins that cause gonad medulla to differentiate into a testis • Which has o Leydig cells • Secrete testosterone (controls development of Wolffian duct into accessory structures • Testosterone converted to DHT with 5a reductase which controls the develpoment of male external genetalia Development of internal male organs 1. SRY gene protein in
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