Sexual differentiation

Question 1

What is the overall process of sex differentiation in humans?

Answer 1

Genome (XX/XY) → Gonad → Sex hormone (oestrogens/testosterone) → Sex characteristics

Question 2

What determines male sex differentiation?

Answer 2

Y chromosome contains SRY gene that codes for testes-determining factor, which drives male sex differentiation. Else the default sex is female.

Question 3

What is the process of male sex differentiation?

Answer 3

1. Y chromosome expresses Sry gene coding for a protein called testes determining factor (TDF).
2. TDF drives the differentiation of primitive sex cord cells (from coelomic epithelium) into Sertoli cells and invading cells from mesonephric duct into Leydig cells.
3. TDF also drives the expression of SOX9, which stimulates production of anti-Müllerian hormone (AMH) by Sertoli cells.
4. AMH promotes degradation of paramesonephric ducts.
5. Leydig cells (derived from mesonephric cells) secrete androgens (mainly testosterone) that sustain the mesonephric duct, which eventually develops into the male internal genitalia (epididymis, vas deferens, seminal vesicles) and external genitalia.

Question 4

What is the process of female sex differentiation?

Answer 4

1. Primary sex cords don’t fully form, and cluster around germ cells to form layer of epithelium, forming the primary ovarian follicles. These differentiate into granulosa cells.
2. Invading mesonephric cells develop into thecal cells.
3. Thecal cells produce androgens that are converted to oestrogens immediately by granulosa cells.
4. In the absence of androgen production, the mesonephric duct regresses and the paramesonephric duct (under oestrogen support) develops into the female internal genitalia (fallopian tubes, uterus, cervix, upper vagina).
5. The female external genitalia develops in the absence of androgens, but does not need the presence of oestrogens.

Question 5

What drives development of the male external genitalia?

Answer 5

Dihydrotestosterone

Question 6

What drives development of the female external genitalia?

Answer 6

Absence of testosterone (no oestrogen required)

Question 7

What are the types of intersex conditions?

Answer 7

1. Primary hermaphroditism: Mutations in Sry/abnormal fertilisation results in expression of both testicular and ovarian tissue (either in mosaic form or testes on one side and ovaries on another).
2. Secondary hermaphroditism: Gonads are normal and produce androgens/oestrogens, but somatic tissue fails to respond, therefore inappropriate internal and/or external genitalia develop.

Question 8

What are the forms of secondary hermaphroditism?

Answer 8

1. Persistent Müllerian duct syndrome: Mutations in AMH result in persistence of Müllerian duct (paramesonephric duct) in males that develop into remnants of female genitalia.
2. Androgen insensitivity syndrome: Mutations in androgen receptor results in development of female/ambiguous external genitalia in males. No development of any internal genitalia.
3. 5α-reductase deficiency: Results in less production of dihydrtestosterone and development of female external genitalia but male internal genitalia in males.
4. Congenital adrenal hyperplasia (21-hydroxylase deficiency): Less production of cortisol results in less feedback and oversecretion of ACTH. Over-production of 17-hydroxyprogesterone which cannot be converted to cortisol and so is converted to androgens. In females, ambiguous external genitalia develops with presence of features of both male and female internal gentialia.

Question 9

What is gender?

Answer 9

Categorising individuals as boy or girl based on anatomical features.

Question 10

What is gender identity?

Answer 10

An individual’s feelings towards whether they should be classified as a man or woman.

Question 11

What is gender stereotype/role?

Answer 11

Socially expected attributes of men/women. This is determined by clothing, hair, interaction with others.

Question 12

What is sexuality?

Answer 12

The part of an individual’s emotional and intellectual make up concerned with the erotic. In other words, the type of people an individual is sexually attracted towards.

Question 13

What is sexual identity?

Answer 13

An individual’s belief in which sex they are attracted to.

Question 14

What is sexual stereotype/role?

Answer 14

Socially expected attributes associated with specific sexualities.