WEEK 5 (Sex determination and sex hormones)

Question 1

What occurs in female development?

Answer 1

• Default development
• Mesonephric duct degenerates and paramesonephric duct develops

Question 2

What occurs in male development?

Answer 2

• The SRY gene on Y chromosome produces testis-determining factor leading to testes development
• Sertoli cells secrete Mullerian inhibitory factor (MIF, called antimullerian hormone) that suppresses development of paramesonephric ducts
• Leydig cells secrete androgens that stimulate development of mesonephric ducts

Question 3

What is the function of Paramesonephric (Mullerian) duct?

Answer 3

Develops into female internal structures (Fallopian tubes, uterus, upper portion of vagina)

Mullerian agenesis (Mayer-Rokitansky-Kuster-Hauser syndrome) may present as 1st degree amenorrhea (due to lack of development) in females with fully developed 2nd degree sexual characteristics

Question 4

What is the function of the Mesonephric (Wolffian) duct?

Answer 4

Develops into male internal structures (except prostate)
S - Seminal vesicles
E - Epididymis
E - Ejaculatory duct
D - Ductus deferens

Question 5

What are first degree sexual characteristics in males?

Answer 5

Internal male genitalia: Seminal vesicle, Epididymis, Ejaculatory duct, Ductus deferens

External male genitalia: Penis, Scrotum, Prostate

Question 6

What are second degree sexual characteristics in males?

Answer 6

• Pubic, axillary and facial hair
• increased penis size/length
• growth spurt

Question 7

What are first degree sexual characteristics in females?

Answer 7

External female genitalia: clitoris, labia, distal vagina

Internal female genitalia: Fallopian tubes, uterus, proximal vagina

Question 8

What are second degree sexual characteristics in females?

Answer 8

• Breast development
• Pubic and axillary hair

Question 9

What are the different regions of the Y chromosome?

Answer 9

• Pseudoautosomal region (PARs)
• Nonrecombining region of the Y (NRY)
• Male-specific region of the Y (MSY)
• Sex-determining region Y (SRY)
• Testis-determining factor (TDF)

Question 10

Y chromosomes are ____________ than X chromosomes

Answer 10

smaller

Y chromosomes have at least 75 genes whereas X chromosomes have 900-1400 genes

Question 11

Paternal age has now been associated with an increased risk in offspring of congenital disorders with a genetic basis collectively known as ___________________

Answer 11

Paternal age effects (PAE)

conditions include:
- certain cancers
- schizophrenia
- autism

Question 12

Define the “primary sex ratio’ (PSR)

Answer 12

reflects the proportion of males to females conceived in a population

Question 13

Define the ‘secondary sex ratio’

Answer 13

reflects the proportion of each sex that is born

Question 14

What is the advantage and disadvantage of the secondary sex ratio?

Answer 14

Advantage - much easier to determine than the primary sex ratio

Disadvantage - doesn’t account for any disproportionate embryonic or metal mortality