Sex Determination and Gonadal Development

Question 1

Sex differentiation depends on the ________ gene on the Y chromosome. In the presence of this factor, male sex organs develop, in its absence, female sex organs develop.

Answer 1

Testis Determining Factor (TDF)

Question 2

What is the indifferent period of gonadal development?

Answer 2

This refers to the first six weeks of intrauterine life when the sex of the embryo is indistinguishable.

Further notes:
It refers to the time and morophological period when the primordial embryonic/foetal structures have full potential of differentiating into either male or female sex organs.
This stage applies to the development of the gonads, the internal genitalia, and the external genitalia.

Question 3

State three embryonic sources of the gonads.

Answer 3

(a) mesothelium (mesodermal lining epithelium) on the posterior abdominal wall
(b) underlying mesenchyme (embryonic connective tissue)
(c) primordial germ cells (earliest undifferentiated sex cells)

Question 4

Comment on the indifferent stage of gonadal development.

Answer 4

A thickened area of mesothelium develops on the medial side of the mesonephros. Proliferation of this epitheilum and underlying intermediate mesenchyme produces a bulge known as the gonadal ridge. It has a cortex and medulla and is the primordium of the testis/ovary.

Question 5

Comment on the indifferent stage of the internal genitalia.

Answer 5

It is marked by the presence of two key embryonic genital ducts - the Wolfian and Mullerian ducts.
The Wolfian (mesonephric) duct is the embryonic primordium of the male internal genitalia.
The Mullerian (paramesonephric) duct is the embryonic primordium of the female internal genitalia.

Further notes:
The Mullerian ducts, also known as paramesonephric ducts, originate from a finger-shaped invagination of the coelomic epithelium at the upper pole of the mesonephros. They run laterally down the side of the urogenital ridge and terminate at the Mullerian eminence in the primitive urogenital sinus. In females, these ducts develop into the fallopian tubes, uterus, cervix, and the upper one-third of the vagina. Male embryos, on the other hand, produce anti-Mullerian hormone, leading to regression of the paramesonephric ducts. Disturbances in this process can result in various reproductive anomalies.

Question 6

State the three stages in sex determination prenatally.

Answer 6

(1) Genotypic (chromosomal) sex determination
(2) Gonadal sex differentiation
(3) Phenotypic (anatomical) sex differentiation