Genetics, sex and gender

Question 1

How is sexual development regulated? What key gene is involved?

Answer 1

Males:
1. genetic factors initiate differentiation of the gonads into testis
2. Activation of sertoli cells which secrete mullerian inhibiting homrones, causing the degenaration of the mullerian ducts
3. Stimulation of the Leydig cells, which secrete testosterone, causing the development of the wolffian ducts owards the epidydimes, vas deferens and seminal vesicles.
The sexual development of men is caused by the genes present on the Y chromosome: it has SRY and SOX9 genes, which cause a molecular cascade that activate sertoli and leydig cells.

Females:
If any of the genes/hormones that is present in male’s development, is absent, then gonads will develop into female’s organs.
The X chromosome contain genes that cause the differentiation of gonadal tissue into ovaries; the absence of testosterone causes the degeneration of wolffian duct; the absence of MIH cause the mullerian ducts to develop into fellopian tubes, uterus and vagina.

Question 2

How does hormonal environment affect sexual phenotypes?

Answer 2

The congenital adrenal hyperplesia is the perfect example for overexposure to synthetic steroid: individuals with this syndrome, are 46XX but present virilization of external genitalia. This is due the excessive production of androgens, caused by genetic defects.

Question 3

What are some genetic defects that affect genotypic-phenotypic sex?

Answer 3

1. Swyer syndrome:
   
   • SRY mutation
   • XY
   • no testis/ovaries
   • female external genitalia
   • defective spermatogenesis
2. Anti-mullerian hormone
   
   • SRY present
   • testosterone
   • cryptorchidism
3. DHT-converting enzyme
   
   • no 5 α-reductase
4. Androgen insensitivity
   
   • 46XY
   • phenotypically female