Chromosomes and hormones in sex and gender

• Chromosomes


  The X shaped bodies that carry genetic information DNA for an animal
• Hormones


  The body's chemical messengers. They travel through the bloodstream and control many different processes including growth, the stress response and bonding between mother and newborn baby
• Intersex


  The term used to describe an individual who is not clearly defined as male nor female because of a mismatch between their chromosomes and genitalia
• Typical chromosome patterns


  • XX (female)
  • XY (male)
• Typical chromosome patterns


  • There is usually a direct link between an individual's chromosomal sex (XX and XY) and their external genitalia (vagina or penis) and internal genitalia (ovaries or testes)
  • During prenatal development all individuals start out the same - a few weeks after conception both male and female embryos have external genitalia that look essentially feminine
• Klinefelter's syndrome


  Due to an XXY chromosome configuration. The individual is born with a penis and develops as a fairly normal male. Approximately 1 in 1,000 males have this condition. Such individuals tend to be taller than average and may have less muscular coordination than average. Physically they look less masculine because of reduced levels of testosterone.
• Turner's syndrome


  Due to an XO chromosome configuration, meaning the second sex chromosome is partly or completely missing. This occurs in about 1 in 2,000 females at birth. Such individuals are born with a vagina and womb. The characteristics include being shorter than average and having a lack of monthly periods due to underdeveloped ovaries.
• Chromosomes do not simply determine a person's sex and they also determine which hormones are produced. The hormone testosterone is produced in much greater quantities in males and the hormones oestrogen and oxytocin are mainly female hormones.
• Testosterone


  Produced primarily (before a baby is born) and affects the development of genitals. However some XY individuals have an insensitivity to such hormones, in their bodies. So do not respond to the effects of the hormones. In extreme cases the consequence is that no external male genitalia develop.
• Oestrogen


  The default gender in a genetic male will develop as a female unless exposed to testosterone. Females do not need hormones to direct penis/genital development. However, there is some evidence of other prenatal factors. For example, some recent research found that oestrogen may actually lead to smaller brain size.
• Oxytocin


  Has been called the 'love hormone' as it promotes feelings of bonding in both men and women. Oxytocin is produced in the pituitary gland and evokes feelings of contentment and calmness. In women the hormone is important in breastfeeding because it causes milk to flow in a lactating mother. In men and women oxytocin is related to caregiving and faster wound healing.
• At times of stress, oxytocin dampens the fight-or-flight response. In females the tend-and-befriend response is triggered (Taylor et al, 2000). This response ensures that females protect their young (tending) and form protective alliances with other women (befriending). The same does not happen in men because stress dampens the effects of oxytocin.
• Biological factors do have a key role in gender development, but other factors such as genetics, hormones, experiences, personal qualities and socialisation/culture also have a key role.
• The eventual outcome for each individual appears to be a complex and unpredictable combination of genes, hormones, ways of rearing and socialisation. The outcome is described as unpredictable because there do not appear to be any simple rules.
• The case of the Batista family in the Dominican Republic illustrates the role of culture - in a community prepared to accept more fluidity in gender roles, it seemed to be relatively easy to move between roles, something which is much more difficult in cultures with more rigid gender norms.
• A greater understanding of intersex conditions has led to real-world applications, such as the Intersex Society of North America recommending that babies with such conditions should be assigned a gender but no surgery should be conducted until the individual can make an informed decision themselves.
• Genetic testing enables certain individuals, such as those with Turner's syndrome, to be identified early so they can then be given hormone supplements to help them develop secondary sexual characteristics and improve their general health.
• Experimental research with non-human animals has confirmed the effects of testosterone on brain development, with male monkeys exposed to test during prenatal development engaging in more rough-and-tumble play and being more aggressive.
• However, human behaviour is governed at least to some extent by expectations and deliberate choice, as shown in a study where women who believed they had been given testosterone behaved in a more unfair way, demonstrating the effect of expectations.