Mental health articles

Male and female sex differentiation
Biological sex may be defined on many levels—ex-determining genes, sex
chromosomes, HY sex-determining antigen, gonads, hormones, internal
reproductive structures or external genitalia. In some infants, sex cannot be
determined as exclusively male or female and complex decisions must be made about sex assignment and surgical intervention.
Genetic sex is established at fertilisation when the genetic material of sperm
and ovum are united. The ovum contains 22 chromosomes and a single X sex
chromosome. The sperm contains 22 chromosomes and either an X or Y sex
chromosome. The normal combination patterns are:
• male—46 XY
• female—46 XX.
There are several variants of this pattern, some of which are associated with
problems of biological sex development and infertility. For example:
• Turner’s Syndrome 45 X—missing X chromosome in a female
• Klinefelter’s Syndrome 47 XXY—additional X chromosome in a male.
The Y chromosome is necessary for the development of male sexual
characteristics. A gene on the Y chromosome known as the ‘sex-determining
region’ (SRY gene) codes for the production of ‘testes determining factor’, which
promotes the development of testes and seminiferous tubules. The testis
produces the male hormones testosterone and androstenedione and a substance
that works to inhibit the development of female (Mullerian) structures, known
as ‘antimullerian substance’. The X chromosome contains genes for ovarian
development and in the absence of male hormones, the course of foetal
development is female.