The role of chromosomes and hormones (testosterone, oestrogen and oxytocin) in sex and gender. Atypical sex chromosome patterns: Klinefelter’s syndrome and Turner’s syndrome

Chromosomes initially determine a person’s sex but most gender development actually comes about through the influence of hormones. In the womb, hormones act upon brain development and cause the development of reproductive organs. At puberty, a burst of hormonal activity triggers the development of secondary sexual characteristics.