BIOL W3006 Fall 2002 Mini-exam #2 NAME______________________________________________

Answers in red. Explanations in blue.

1. (10 pts) Females are sometimes born who have 5-alpha reductase deficiency. As adults, they resemble normal women in most regards, but one difference is that they have very little body hair. This suggests that in normal women, body hair growth depends on the presence of

a. estrogen b. cortisol c. progesterone d. DHT e. aromatase 5-alpha reductase converts T to DHT, so the enzyme deficiency means that DHT won’t be produced.

2. (10 pts) Careful observation of a developing human embryo shows that the Mullerian ducts start to regress in week 7, while the Wolffian ducts start to develop in week 8. This would lead you to suspect that in the testes, the __Sertoli__ cells develop before the ___Leydig__ cells. Sertoli cells secrete MIH, which causes the Mullerian ducts to start to regress in week 7. In week 8, the Leydig cells start secreting testosterone, which is needed for Wolffian duct development.

3. (8 pts) Oocytes develop in the _________ of the indifferent gonad. a. cortex b. medulla

4. Early in the follicular phase, about 20 follicles start to develop, but eventually 19 of them degenerate. This degeneration is partly caused by androgens. The accumulation of androgens in a follicle causes it to degenerate. (20 pts)

A. Which cells do these androgens come from? Thecal cells 3 pts.

B. What stimulates their production there? LH 3 pts

C. Why are they produced? The androgens are precursors for the estrogen produced by granulosa cells. 4 pts

D. What event in the menstrual cycle causes them to accumulate? Explain. 10 pts

Early in the cycle, 20 follicles start to develop, but only one of them will ovulate…. The rest degenerate. FSH stimulates receptors on the granulosa cells, leading to increased activity of the aromatase, which converts androgens to estrogens. If FSH were not present, the androgen wouldn’t be converted to estrogen, and so would accumulate in the follicle. There is a decrease in FSH before ovulation, caused by negative feedback by estrogen and by inhibin.

5. Consider the situation of an individual who has normal XY chromosomes, but has a mutation in the gene for the LH receptor, so that this receptor cannot function at all. Describe the sexual differentiation of this person below. For each part, explain what causes differentiation in this direction. Your explanation should make it clear that you understand what causes normal differentiation of this structure, and how it is (or is not) different in this person.

(32 points: 3 pts each structure, 5 pts each explanation)

A. What kind of gonad will this person have?

Testes. Testes normally develo in males if the Y chromosome, containing the SRY gene, is present. Here, the Y chromosome is normal, so testes should develop.

B. What will happen to the Mullerian ducts?

Regress. Testes normally secrete MIH, which causes Mullerian ducts to regress. This should occur normally here, since MIH is not dependent on LH.

C. What will happen to the Wolffian ducts?

Regress. In response to LH, testes secrete testosterone, which causes the Wolffian ducts to develop into the vas deferens and epididymis. Since the person here can’t respond to LH, no testosterone will be secreted, so the Wolffian ducts will regress.

D. What kind of genitals will this person have?

Female. Genital differentiation in the male direction depends on DHT, which is produced from T. Since there’s no T (as explained in part C.), there’s no DHT, so the genitals follow the default pattern of development, which is female.