Determination of Sex

Question 1

• Advantages of sexual reproduction? (2)

- X inactivation? Implications? (4)

Answer 1

• Increased genetic variability by increased evolution; protects species
• Female inactivate 1x; all dipoid have active x; females are mosaic for x’s; inactivation via methylation; Xist inactivates Cis (self) to form Barr Body; non random process

Question 2

Sex differentiation:

• Leads to teste development? Encodes what TF?
• Mechanism?
• Anatomic progression? XY? (6) XX (3)
• Leads to internal reproductive organs?
• Sex and CNS?

Answer 2

• SRY; HMG box capable of opening chromosome
• SRY acts on Sox9 to inhibit dupDAX (leads to ovaries if not inhibited)
• XY –> SRY Gene –> Testes –> MIF and Testosterone produces –> Testosterone actively makes mesenephric ducts; MIF actively degrades Paramesenephric ducts
• XX –> Ovary –> Passive development and degradation of ducts
• XY = MIF presence
• Dimorphic b/n sexes