Role of Chromosomes & Hormones

• A person's sex is determined by their biological status of being either male or female. This is usually categorised based on the genitals a person has, but their biological sex is determined by their chromosomes and hormones.
• Chromosomes carry genetic material that make every individual unique, this is their genotype.
• Humans have 23 chromosome pairs, with one of each pair inherited from either parent.
• Humans have 46 chromosomes which are arranged in pairs of which only one is sex linked to X or Y.
• The sex chromosomes are found on the 23rd pair and are either XX if they are female and XY if they are male.
• All normal egg cells produced by a human ovary have an X chromosome. Sperm carry an X or Y chromosome. The baby's sex is determined by the sperm that fertilises the egg cell.
• The sex chromosomes instruct the body as to how to develop in terms of the gender pathway. This will also influence which hormones the body is exposed to.
• In prenatal development sex chromosomes tell the body which reproductive organs to develop. They also send a signal to the sex organs to begin to produce hormones.
• Chromosomes initially determine a person’s sex but most gender development actually comes through the influence of hormones.
• During prenatal development, individuals have sex glands (gonads) which are identical and have the ability to turn into either testes or ovaries.
• The Y chromosome contains a gene called sex determining region Y (SRY), this tells the sex organs to become testes. The production of testosterone then influences the developing foetus to take on male characteristics, including a masculinised brain.
• The SRY gene causes testes to develop in an XY embryo, these then produce androgens which are male sex hormones.
• Androgens are a group of chemicals associated with male development, the most widely known of which is testosterone.
• In Psychology if a research study is biased towards males it is said to be androcentric (male based bias).
• The lack of a Y chromosome in the XX embryo will mean there is no SRY gene. And no instruction for the sex organs to develop into testes. Instead ovaries are developed and the foetus takes a female pathway.
• The female pathway which began with XX chromosomes encourage the ovaries to produce female hormones such as oestrogen. This will then feminise the body as well as the developing brain.
• If a Y chromosome is present, it produces a protein which causes the gonads to become testes, which will eventually produce testosterone and lead to the development of male sex organs.
• Without the presence of a Y chromosome, the male pathway cannot take place and therefore female sex organs develop.
• Hormones associated with males such as testosterone are also found in females. It is often assumed that hormones are typically male or female, when in fact they are found in different concentrations in both males and females.
• Hormones such as testosterone affect gender development in the womb, with males being exposed to more testosterone, which may explain the differences found between a male and female brain.
• Beeman (1947) castrated male mice and found that aggressiveness reduced. He later injected the mice with testosterone which re-established their aggressiveness, which is arguably a male trait.
• Oestrogen is a hormone produced by the ovaries linked to the female reproductive cycle and is found in higher levels in females from puberty.
• Oxytocin is a neuropeptide produced in the hypothalamus in the brain and secreted by the pituitary gland during child labour.
• Oxytocin is also known as the love hormone as it is believed to encourage bonding between a child and it's mother. It is also produced in males and females while kissing, leading to positive emotions.
• The hormone oxytocin is thought to reduce stress and promote feelings of love and intimacy between couples.
• Women typically produce oxytocin in much larger amounts than men, particularly as a result of giving birth.
• Oxytocin stimulates lactation making it possible for mothers to breastfeed their children. It also reduces the stress hormone cortisol and facilitates bonding.
• Hormones have an influence on gender development at several stages of the maturation process.
• Hormones act upon brain development prenatally in the womb and cause the development of the reproductive organs. They act again during adolescence when people reach puberty. This triggers the development of secondary sexual characteristics which differ between males and females.
• Hormones influence the development of sex organs by flooding the womb with an influx of either testosterone or oestrogen.
• Albrecht & Pepe (1997) found that giving oestrogen to pregnant baboons reduced miscarriage, suggesting that oestrogen is associated with successful pregnancy.
• Hormones affect the development of a foetal brain and can masculinise or feminise the brain.
• Money & Ehrhardt (1972) found that girls whose mothers took medication containing testosterone during pregnancy showed more masculine traits.
• Differences in hormonal influence may explain structural differences in the brains of males and females.
• Bryden & Saxby (1985) found that when males perform spatial tasks, there is greater electrical activity in the right hemisphere, whereas females seem to use both hemispheres.
• Testosterone is a male hormone although it is present in small quantities in women.
• According to evolutionary explanations, high levels of testosterone are linked to aggressive behaviour.
• Wang et al (2000) investigated the link between increased testosterone and sexual behaviour. They studied 227 hypogonadal (low testosterone) men for 180 days and found testosterone replacement had a significant effect on their body.
• O'Connor et al (2004) increased testosterone levels in healthy young men and found no significant changes in their sexual or aggressive behaviour.
• Oestrogen is a female hormone that determines female sexual characteristics and menstruation.