role of chromosomes and hormones in sex/gender

• Everyone has 23 pairs of chromosomes in each cell. Each of these carries hundreds of genes with instructions about physical and behavioural characteristics. One pair of chromosomes are the sex chromosomes, they determine the sex. The female this pair is called XX as both chromosomes are shaped like Xs. The male chromosome pair is XY. The Y carries little genetic material, but it does determine the sex of the child. A few weeks after contraception both have genitalia that looks feminine. When the foetus is 3 months old, testosterone is produced in males and external genitalia develops.
• There are atypical patterns of sex chromosomes. Klinefelter’s syndrome is due to an XXY configuration. The individual is born with a penis and develops as a fairly normal male. Approximately 1 in 1,000 males have this. Such individuals tend to be taller than average and less muscular coordination than average. Physically they look less masculine due to reduced levels of testosterone, such as less facial hair, broader hips and breast tissue. Often infertile.
• Turners syndrome is due to an XO 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 a womb. The characteristics include, shorter than average and a lack of monthly periods. There are a range of other characteristics such as a webbed neck, narrow hips and smaller lower jaw. No two XO females have the same characteristics.
• The chromosomes determine the sex, but also which hormones are produced. Testosterone is produced prenatally and affects the development of genetalia. Some XY individuals don’t respond to the effects however, in extreme cases no external genitalia develops. The surge of testosterone during puberty is responsible for secondary sexual characteristics (facial hair and a deepening voice). Females aren’t exposed to hormones prenatally for development of genitalia. Research has found that oestrogen may actually lead to smaller brain size
• Oestrogen plays a major role from puberty onwards influencing things such as breast development. Oxytocin has been called the ‘love hormone’ as it promotes feelings of bonding both in men and women. It is produced in the pituitary gland evoking feelings of calmness. It is important in breast feeding and it causes the milk to flow. At times of stress it dampens the fight or flight response so females produce tend and befriend as testosterone dampens this.

   
• A study on non-human animals confirms the effects of testosterone on brain development.

  Quadago found that female monkeys who were deliberately exposed to testosterone during prenatal development later engaged in more rough play than other females and were more aggressive. Eisenegger did a study of observing a bargaining game. those who believed they had been given testosterone behaved more unfair than those who believed they were given a natural placebo.

  This research suggests that hormones do influence brain development and human behaviour, but relationship isn’t simple.
• a greater understanding of intersex conditions has led to real-world applications.

  In the past surgery was used to make them look 'normal'. Now it is recommended that babies with such conditions should be assigned a gender, but no surgery conducted till they can choose themselves. Genetic testing now also allows individuals with Turners syndrome to be identified early and hormone supplement.to help them develop secondary sexual characteristics and said to improve their general health.  This shows how psychological research can contribute to improving peoples lives.  
• John money may have been wrong in claiming that biological sex was not the main factor in gender development. 

  He argued that sex of rearing was much more important and intersex individuals (daniel reimer) could be successfully raised as either a boy or a girl. Further supported by research on 16 genetic males (no penis almost), 2 raised as males rest as females. Of the rest, 8 reassigned themselves to males by age 16.

  Such research suggests that biological factors do have key role in gender development. 
• However, genes and hormones are not the whole story. Genetic sex does not match external genitalia in cases of abnormal hormone exposure. The outcome appears to be unpredictable combination of genes and hormones. For example, CAH occurs when XX females have prenatally high levels of male hormones resulting in varying degrees of external male genitalia. Thus gender development must be in part biologically determined (nature) but experience, personal qualities and socialisation (nurture) also have a key role.