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.
• Normal Oocte growth requires the activity of both X chromosomes.

External Genetalia

Turner's Syndrome

Kleinfelter's Syndrome

Testicular Feminisation

Adrenogenital Syndrome

Hermaphroditism

Bovine Freemartinism