Determinasi Sex Mammals

1. Determinasi Sex Mammals

2. Sex determination • Primary sex determination • Secondary sex determination

3. Primary sex determination • is the determination of the gonads • In mammals, primary sex determination is  chromosomal and is not usually influenced by the environment • The female  XX and the male  XY • Every individual must have at least one X chromosome

4. Female  her eggs has a single X chromosome The male  two types of sperm: half bear the X chromosome, half the Y • If the egg receives another X chromosome from the sperm, the resulting individual is XX  forms ovaries  is female • if the egg receives a Y chromosome from the sperm, the individual is XY  forms testes  is male

5. Y chromosome carries a gene  encodes a testis-determining factor • Y chromosome  organizes the gonad  testis rather than an ovary • The mammalian Y chromosome is a crucial factor for determining sex in mammals • Five X chromosomes and one Y chromosome (XXXXXY) would be male

6. A single X chromosome and no second X or Y (i.e., XO)  develops as a female: ovaries (follicles cannot be maintained) • A complete ovary  a second X chromosome (XX) is needed • In mammalian  formation of ovaries and testes are both (X,Y) active

8. Secondary sex determination •  affects the phenotype outside the gonads • A male mammal has a penis, seminal vesicles, and prostate gland • A female mammal has a vagina, cervix, uterus, oviducts, and mammary glands • These secondary sex characteristics  by hormones secreted from the gonads

9. In the absence of gonads, the female phenotype is generated • Fetal rabbit gonads  removed before differentiated  the resulting  female phenotype (XX or XY)  had oviducts, a uterus, and a vagina, and each lacked (-) a penis and male accessory structures

10. If the Y chromosome is absent, the gonadal primordia develop → ovaries • The ovaries produce estrogen → development of the Müllerian duct into the uterus, oviducts, and vagina • If the Y chromosome is present, testes form and secrete two major hormones: anti-Müllerian duct hormone and testosterone

11. Hormone 1. anti-Müllerian duct hormone (AMH or Müllerian-inhibiting substance, MIS)  destroys the Müllerian duct 2. testosterone  masculinizes the fetus, stimulating the formation of the penis, scrotum, and inhibiting the development of the breast primordia

12. Hormon Wolffian Müllerian penis, scrotum, and inhibiting breast primordia uterus, oviducts, and vagina Male Female

13. The developing gonads • All other organ rudiments can normally differentiate into only one type of organ: • A lung rudiment  become only a lung • A liver rudiment  develop only into a liver • But the gonadal rudiment  two normal options  develop into either an ovary or a testis. • The mammalian gonad first develops through a bipotential (indifferent) stage neither female nor male characteristics.

14. Indiferent Gonad (4 weeks)

15. Indiferent Gonad (6 weeks)

16. The developing of male • If the fetus is XY → the sex cords → proliferate → cords fuse, forming a network of internal sex cords → at distal end → rete testis • The sex cords → now called testis cords → the tunica albuginea • The germ cells are found in the cords  in the testes • During fetal life and childhood, the testis cords remain solid

17. Indiferent Gonad (8 weeks):  Testis Development

18. At puberty, the cords → the seminiferous tubules and the germ cells → differentiate into sperm • The cells of the seminiferous tubule are called Sertoli cells. • The Sertoli cells of the testis cords → the sperm and secrete anti-Müllerian duct hormone • The sperm are transported from the testis → the rete testis → the efferent ducts

19. Indiferent Gonad (16 weeks): Testis Development

20. The efferent tubules  the mesonephric kidney → link the testis to the Wolffian duct  used to collecting tube of the mesonephric kidney • In males, the Wolffian duct differentiates to become the epididymis, vas deferens and urethra  the tube through the sperm pass out of the body • During fetal development, the interstitial mesenchyme cells of the testes differentiate into Leydig cells, which make testosterone

21. The developing of Female • In females, the germ cells will reside near the outer surface of the gonad • Unlike the sex cords in males  the initial sex cords of XX gonads degenerate • The epithelium soon produces a sex cords → stay near the outer surface of the organ → called cortical sex cords

22. Indiferent Gonad (8 weeks): Ovarian Development

23. These cords  split into clusters  each cluster surrounding a germ cell. • The germ cells  become the ovary  surrounding cortical sex cords  differentiate into the granulosa cells • The mesenchyme cells of the ovary differentiate into the thecal cells • Thecal & granulosa cells  form the follicles envelop the germ cells & secrete steroid hormones

24. Indiferent Gonad (20 weeks):  Ovarian Development

25. Each follicle  contain a single germ cell • In females, the Müllerian duct remains intact  differentiates into the oviducts, uterus, cervix, and upper vagina. • The Wolffian duct  deprived of testosterone  degenerates

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