the role of hormones and chromosomes in sex and gender

• During pregnancy and a few weeks after conception, both male and female embryos have external genitalia that are essentially female. Once the foetus is 3 months old, if it is to develop into a male, the testes produce testosterone which causes the external male genitalia to develop. Genetic transmission therefore explains how individuals acquire their biological sex as well as aspects of gender and their sense of whether they are male or female.
• klinefelter's syndrome


  • XXY chromosomes
  • The individual would develop into a reasonably normal male although they may be taller than average, have less muscular coordination than average and look less masculine because of lower levels of testosterone. This may result in less facial hair, broader hips and potential breast tissue with many often being infertile. Psychological effects include poor language skills that affect reading ability and a noticeable passive temperament, attention problems and an increased risk of anxiety disorders and depression.
• turner's syndrome


  • XO chromosome configuration
  • Affected individuals are born with a vagina or womb with characteristics that include them being shorter than average, lacking monthly periods due to underdeveloped ovaries, small lower jaw, webbed neck, narrow lips and misshapen internal organs. 
  • heart conditions, high blood pressure, urinary complaints, vision and hearing problems and osteoporosis. Psychological problems include social adjustment due to their physical appearance and minor learning difficulties. higher than average reading ability
• Males produce testosterone at much greater quantities while oestrogen and oxytocin are mainly female hormones. Gender development is mostly attributed to hormones.
• The influence of testosterone begins early in pregnancy and affects the development of genitalia as well as the brain and behaviour. The gonads are sex glands with testes in males and ovaries in females and originally these are both identical in both XY and XX embryos. However with XY individuals (biological males), genetic information in the Y chromosome causes the gonads to become testes and by the 8th week of gestation, they begin producing hormones, primarily testosterone.
• SRY gene


  The SRY gene within the Y chromosome controls whether the gonads will develop into testes or ovaries.
• testosterone also affects brain development both prenatally and later in childhood e.g XX females exposed prenatally to large doses of male hormones later showed more tomboyish behaviour and greater interest in male-type activities
• surge of testosterone during puberty is responsible for secondary sexual characteristics such as facial hair and deepening voice
• oestrogen - females do not need hormones to direct prenatal genital development. oestrogen plays a major role from puberty onwards promoting secondary sexual characteristics and directing the menstrual cycle
• oxytocin - called the 'love' hormone as it promotes feelings of bonding in both men and women. it is produced in the pituitary gland and evokes feelings of calmness. it is important in women who are breastfeeding because it causes milk to flow in a lactating mother. oxytocin dampens fight or flight response. in females the alternative tend and befriend response is triggered . this response ensures they protect their young and form protective alliances with other women.
• • 23rd chromosome pair determines biological sex.
  • testes develop due to area on Y chromosome
• SRY gene triggers development of testes and stops development of ovaries