Beginner's guide to genetics: Sex and genetics

Throughout history, humans have tried to discover differences between men and women, and how this determines the nature of sex. In the last century, scientists began to unlock the molecular and genetic mechanisms of sexual development. This process has not been so simple, however; sexual development consists of an orchestrated, ordered, and interrelated cascade of events.

The first step is the establishment of genetic sex (XX or XY). This results when a spermatozoid with an X or Y chromosome (genetic sex) fertilises an oocite, which carries an X chromosome. The second step is development of sex gonads. At the beginning of this step, regardless of genetic sex, embryos develop a bipotential primordium--a structure in the forming embryo that can turn into female or male gonad. This then differentiates to form the testis in XY embryos or the ovary in XX embryos, thereby defining gonadal sex. The last step is phenotypical sexual differentiation, when sexual external and internal genitalia develop due to hormones secreted by the gonad, resulting in the physical characteristics of each specific sex.

Finally, the gender of a person is the rearing assignated sex--the psychosocial implications of sex, which comprises determination and differentiation processes. Sex determination is the genetic events leading to male or female gonadal development; and sexual differentiation is the subsequent steps leading to functional sexuality and secondary sexual characteristics.