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Sex Determination

Sex Determination

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Sex Determination

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  1. Sex Determination • Chromosomal Sex Determination • Primary and Secondary Sex Determination • Another model of chromosomal sex determination: Drosophila • Environmental Regulation of Sex Determination

  2. Mammalian Sex Chromosomes • Formation of bipotential gonad. • Males= XY • Females= XX • Sex determined by Y chromosome- SRY gene

  3. Bipotential Gonad Formation • Intermediate Mesoderm • Mesonephric tubules

  4. Bipotential Gonad Formation WT1 Wnt4 SF1 Sox9 FGF9 GATA4 • Intermediate Mesoderm • Mesonephric tubules

  5. Bipotential Gonad Formation • Intermediate Mesoderm • Mesonephric tubules • Formation of Sex specific gonads

  6. Bipotential Gonad Formation • Intermediate Mesoderm • Mesonephric tubules • Formation of Sex specific gonads • Reorganization of ducts Figure 14.3

  7. SRY Gene • Only on Y Chromosome • Upregulates Sox9

  8. Boy or Girl? Chromosomes: XX Bipotential Gonad Wnt4, R-spo1 b-catenin Sox9 Ovary

  9. Boy or Girl? Chromosomes: XY Anti Mullerian Factor (AMF) Fgf9 Sf1 Bipotential Gonad Sry, Sf1 Sox9 Testes b-catenin

  10. Sox9: Autosomal Testis-determination gene

  11. Secondary Sex Characteristics: Females • Estrogen • Fig. 14.3

  12. Secondary Sex Characteristics

  13. Male Phenotype: Testosterone and AMF • AMF: blocks development of MüllerianTube • Testosterone and dihydrotestosterone

  14. Genetics of Secondary Sex determination • Hermaphrodites: Having secondary sex characteristics for both genders • Androgen Insensitivity Syndrome • Chromosomal Translocation of SRY • Pseudohermaphroditism • Congenital Adrenal Hyperplasia Caster Semenya

  15. Sex on the Brain • SRY and the brain • Aromatase • Gyandromorphs: Some body parts male, some female • Bird Gyandromorphs

  16. Sex on the Brain • Most Mammals, estrogen (estradiol) masculinizes the brain • a-Fetoprotein • Prostaglandin E2 (PGE2)-growth of areas in male brain involved in sexual behavior (hypothalmus, limbic system)

  17. Drosophila Sex Determination • XX/XY • Previously called X:A ratio • Sex-Lethal (Sxl)

  18. Sxl Dosage and Sex Determination

  19. RNA splicing and Sex Determination

  20. Fruitless: Mating Behavior

  21. Environmental Sex Determination • Temperature • Location, Location, Location

  22. Temperature and Reptiles

  23. Temperature and Estrogen

  24. Environment and Sex Determination: Atrazine • Polychlorinated biphenyl compounds (PCBs) act as estrogens • Atrazine: Weed killer • As low as 0.1 ppb can have gonadal/sexual anomalies in male frogs. • U.S. Drinking water= 3 ppb • Midwestern water = ~224 ppb • Hayes et al (2002) found that 7 of 8 sites in Midwest contain Atrazine. • AtrazineupregulatesAromatase PCBs Atrazine

  25. Location