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
Intermediate Mesoderm
Mesonephric tubules
WT1
Wnt4
SF1
Sox9
FGF9
GATA4

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? Sox9 Chromosomes: XX Bipotential Gonad Wnt4, R-spo1
b-catenin
Sox9
Ovary

9. Boy or Girl? Sox9 Chromosomes: XY Anti Mullerian Factor (AMF)
Bipotential Gonad
Anti Mullerian Factor (AMF)
Fgf9
Sf1
Sry, Sf1
Testes
Sox9
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 Müllerian Tube
Testosterone and dihydrotestosterone

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

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.
Atrazine upregulates Aromatase
PCBs
Atrazine

25. Location