chromosomes

• Biopsychologists


  Assume that gender identity and role arises from biological processes
• Gender differences


  Result of sex differences, i.e. women and men act, think and feel differently because of differences in how their brains work
• Brain differences


  May result from chromosomal and hormonal differences
• Biological sex


  Determined by genes
• Chromosomes in humans


  • 23 pairs which carry genes controlling different charcteristics
  • One pair (sex chromosomes) determines sex
• Females


  Have two X chromosomes (XX)
• Males


  Have an X and Y chromosome (XY)
• Chromosomal sex (XX and XY)

  Linked to internal genitalia (ovaries or testes) and external genitalia (vagina or penis)
• Prenatal development


  1. All individuals start out the same

  2. A few weeks after conception both male and female embryos have external genitalia that look essentially feminine

  3. In male embryos, the SRY gene on the Y chromosome causes the gonad to develop into testes (which then secrete testosterone)

  4. Testosterone stimulates the development of the male sex organs and causes the male brain to develop differently from the female brain

  5. A female's gonad will develop into ovaries due to the absence of the SRY gene
• Testes/ovaries


  Strongly influence gender development, through the effects of the hormones they produce
• Reiner and Gearhart (2004) studied 14 children born with cloacal exstrophy (a severe birth defect where much of the abdominal organs are exposed, often causing the splitting of both male and female genitalia) who were reassigned female at birth (born genetically male)
• Follow-up between the ages of 5 to 16 showed that 8 of the 14 who were reassigned identified themselves as boys (i.e. their gender identity matched their genetic sex)
• All of the participants had at least moderately male-typical attitudes and interests
• This provides some support for the argument that biological variables have an impact on gender identity and behaviour, independent of socialisation (nurture)
• David Reimer's biological sex was male (XY), but despite being raised as a female and receiving female hormone treatment, he never fully came to identify himself as a female, and at the age of 13 reverted to his true sex- male
• It has been argued that the size of the SDN (Sexually Dimorphic Nucleus) is determined by levels of testosterone in the womb, and as David was exposed to normal levels of testosterone in the womb, his brain was arguably masculinised