chromosomal sex

chromosomal sex PowerPoint PPT Presentation


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. . Sexually indifferent stage. initially, gonads, sex accessory ducts and external genitalia are identical for both sexes. . . Genital ridges. appear as

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chromosomal sex

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1. Chromosomal Sex sex is determined by chromosomes at fertilization XX = female, XY = male X chromosome contains many genes necessary for survival Y chromosome contains very few genes important gene on Y chromosome: SRY gene SRY = sex-determining region on the Y chromosome

3. Genital ridges appear as “gonadal ridges” near midline at back of abdominal cavity two regions: outer cortex, inner medulla contain no germ cells lasts from 5th to 7th week

4. Undifferentiated Ducts Wolffian ducts (will go on to form male accessory structures) Mullerian ducts (will go on to form female accessory structures)

5. Indifferent external genitalia genital tubercle (will form penis or clitoris) urogenital folds (will form part of penis or labia minora) labioscrotal swelling (will form scrotum or labia majora)

6. Primordial germ cells originate in yolk sac migrate to region of gonadal ridges (by ~5 weeks) proliferate en route in females, germ cells colonize cortex and medulla degenerates in males, germ cells colonize medulla and cortex degenerates

7. Female gonadal differentiation germ cells move into cortex differentiation into ovary occurs ~12 weeks oogonia undergo mitosis and then arrest in early meiosis as primary oocytes

8. Differentiation of female genitalia, sex accessory structures if testosterone isn’t present, genitalia feminize: tubercle > clitoris urogenital folds > labia minora labioscrotal swelling > labia majora Mullerian ducts become oviduct, uterus, cervix, vagina Wolffian ducts regress

9. Think, pair and share Explain how the genital tubercle, urogenital folds, and labioscrotal swellings form mature female genitalia upon differentiation. How do these structures form mature male genitalia?

10. Male gonadal differentiation occurs weeks 6-7 requires expression of SRY gene (Sertoli cells?) germ cells enter medulla, cortex regresses day 60, Leydig cells appear > secrete testosterone

11. Differentiation of male sex accessory structures testosterone “rescues” Wolffian ducts > epididymis, vas deferens, seminal vesicles, ejaculatory duct Sertoli cells secrete Mullerian inhibiting substance (MIS) MIS causes regression of Mullerian ducts

12. Differentiation of external genitalia Masculinization depends on conversion of testosterone to DHT (via enzyme 5 alpha reductase) if DHT present, genitalia assume male phenotype (8th week) tubercle > penis urogenital folds > ventral aspect of penis labioscrotal swelling > scrotum

13. Disorders of sexual development INTERSEXUALITY > ambiguous reproductive systems True hermaphrodites: combination of gonadal tissues present probably due to mosaicism sometimes, ovary and Mullerian duct develop on one side, testis and Wolffian duct on the other Pseudohermaphrodites: gonads agree with chromosomal sex Some aspect of reproductive phenotype resembles that of opposite sex

14. Testicular Feminization Syndrome (MERMs) due to insensitivity to androgens (testosterone, DHT) patients have male chromosomes, normal testes and secrete testosterone unable to respond to testosterone result > female external genitalia; Wolffian ducts don’t differentiate Mullerian ducts will disappear since Sertoli cells still secrete MIS

15. Guevodoces (MERMs) “eggs at twelve” common in remote villages of Dominican Republic chromosomal males, but female external genitalia at birth due to deficiency in enzyme 5 alpha reductase (converts testosterone to DHT)

16. Guevodoces, cont’d. normal testes present; Wolffian ducts differentiate at puberty, high levels of testosterone override deficiency in 5 alpha reductase external genitalia is converted to male phenotype at puberty usually continue life as a male

17. Female Pseudohermaphroditism known as “ferms” chromosomal females with ovaries external genitalia becomes masculinized often due to congenital adrenal hyperplasia adrenal glands are unable to make stress hormone cortisol > secrete androgens instead causes masculinization of external genitalia can also cause early secondary male sex characteristics

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