A01

• Outline the role of chromosomes

  The chromosomal pattern of a male and female is determined at fertilisation and the genetic information on the 23rd pair of chromosomes determines biological sex
• Outline the role of hormones

  Chemical messengers that are released into the bloodstream from glands that control and regulate the activity of certain cells and organs
• State the typical chromosomal structure for females and males

  XX for females and XY for males
• State the main hormones involved in sex and gender

  Testosterone, oestrogen and oxytocin
• Explain how biological sex is determined

  - Chromosomes (the sperm that fertilises the egg cell) determine a baby's sex at fertilisation - all normal egg cells carry an X chromosome, and sperm carry an X or Y chromosome

  - If the egg is fertilised by a Y chromosome carrying sperm, the child will be male and if the sperm carries an X chromosome, then the child will be female
• Explain the role of hormones prenatally

  - An individual's chromosomal pattern alters the hormones released pre and postnatally, the hormones released prenatally influence which internal and external genitalia the foetus will develop

  - All embryos begin with gonads which, depending upon the hormones released, either turn into testes or ovaries, gonadal differentiation occurs around six weeks after fertilisation
• Describe how the production of testosterone determines sex

  - The Y chromosome carries the sex-determining region (SRY) gene which inhibits the release of oestrogen and initiates androgen (testosterone) production which triggers the development of male phenotypes and characteristics of a male

  - Testosterone also affects the development of secondary sexual characteristics during puberty which are triggered by sexual organ maturity
• Describe how the production of oestrogen determines sex

  - If there is no Y chromosome, then oestrogen production continues and initiates the development of female phenotypes and characteristics of a female

  - Oestrogen plays a critical role postnatally as it directs the menstrual cycle and triggers secondary sexual characteristic development
• Describe the role of oxytocin

  A hormone produced in the hypothalamus which controls key aspects of the reproductive system (testosterone inhibits its action in males) especially labour and breast-feeding in mothers, as well as nurturing / bonding behaviour in both sexes
• State the case study which supports the biological explanation for gender

  David Reimer