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sex_gender_final_review_-_yale - "Chapter 1 Sex...

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“Chapter 1”: Sex Meiosis—reduction division of cells where chromosomal content of germ cells is halved. Mitosis—normal cell division that produces genetically identical cells to the parent. Parthenogenesis—form of asexual reproduction. Females are homogametic because they have two X’s. Males are heterogametic because they have an X and a Y. Gonad (ovaries or testis) comes from one indifferent and BIPOTENTIAL precursor. Generally speaking, presence of Y chromosome determines whether ovaries or testis develop. General Rule: If Y chromosome absent female gonads develop. If Y present male gonads develop (testis). But there are some gonadal males with XX chromosomes and some gonadal women with XY chromosomes. How can this occur??? B/c it’s actually SRY , a gene usually on the Y chromosome that stands for “sex- determining region,” that directs gonadal sex. If this gene is somehow present on the X chromosome (because of translocation), a chromosomal woman will develop testis. If it is missing on the Y chromosome, an XY chromosomal male will not develop testis. Thus, SRY specifically determines whether male gonads develop (converts an indifferent gonad into a testis). Specifically, the gene issues the instruction to “make a Sertoli cell”. Primary hermaphrodites have both ovarian and testicular tissues. This is very rare and happens when there is a mixture of XY and XX (or XO) cells. --default development as female and requires no hormonal intervention from the ovaries. --testes secrete two essential hormones however: ANDROGENS and MIS (Mullerian Inhibiting Substance). These hormones are messengers of masculine sexual differentiation sent out by the testis. --ANDROGENS and MIS divert the fetus from default feminine sexual differentiation and into the male process instead. Internal genitalia develop from different unipotential precursors through action/inaction of ANDROGEN and MIS: --Both males and females start out with two separate sets of unipotential primordia, the Wolffian (male) and Mullerian (female) ducts. --Mullerian ducts develop into oviducts, uterus, cervix. --Wolffian ducts develop into epididymis, vas defens, seminal vesicles --In the male, ANDROGEN and MIS prevent the otherwise-automatic development of the female internal genitalia. ANDROGENS maintain the Wolffian ducts. MIS prevents development of the female Mullerian ducts.
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The primordia (precursors) of the external genitalia are BIPOTENTIAL, meaning that both male and female external genitalia arise from the same tissue. --Once again, female external genitalia develop without needing any ovarian endocrine activity. --ANDROGENS secreted by male testis cause male external anatomy. Secondary hermaphrodites—have genitalia that are not of the sex expected from their gonads.
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