Sexual Differentiation - Anatomy & Physiology

Genetic Sex

Established at the time of fertilisation.
The foetus receives its genetic endowment in two equal portions from the male gamete (Spermatozoon) and female gamete (Oocyte).
The X sex chromosome is larger than the Y sex chromosome.
Females have XX chromosomes. All oocytes contain one X chromosome, they are the homogametic sex.
Males have XY chromosomes. Spermatozoa form two distinct populations, one containing X chromosomes and one containing Y chromosomes. They are the heterogametic sex.

The Y chromosome is required to initiate male development.
In absence of the Y chromosome, female gonads (Ovaries) will develop.
The prime male determining gene is SRY (sex determining region of the Y chromosome.

SRY is a very small piece of DNA that acts as a molecular switch to regulate structural genes and autosomal chromosomes, determining if and when they are to be activated.
The presence of SRY alone is sufficient to ensure development of male gonads (Testes).
Female is the default sex, in absence of SRY female gonads (Ovaries) will develop.

Subsequent gonadal development is dependent on a normal population of germ cells.