The Role of Chromosomes & Hormones (AQA A Level Psychology): Revision Note

The role of chromosomes in biological sex

• Chromosomes are made of nucleic acids (mainly DNA in humans) and protein; they are found in the nucleus of cells

• Humans have 23 pairs of chromosomes in each cell; the 23rd pair determines the baby’s sex

  • The chromosome genotype for a male is XY (one of the pair looks like an X and one looks shorter, like a Y)

  • Females have two of the larger X chromosomes, so their genotype is XX

• Chromosomes determine a baby’s sex at fertilisation, as all eggs carry an X chromosome

  • If the egg is fertilised by a sperm carrying a Y-chromosome, the child will be male: XY genotype

  • If the sperm carries an X chromosome, then the child will be female: XX genotype

• The Y chromosome carries the SRY gene, which, during prenatal development, causes testes to develop in an XY embryo; this then produces androgens

  • Androgens cause the embryo to become male, and without them, the embryo develops into a female

The role of hormones in biological sex

• Hormones are chemical messengers that are released into the bloodstream from glands

• Most sex development is a result of the influence of hormones prenatally in the uterus, which act upon brain development of the foetus and cause the development of reproductive organs (testes or ovaries)

• During puberty, hormonal activity triggers the development of secondary sexual characteristics, e.g., pubic hair

• Males and females produce the same hormones but in different concentrations, such as:

  • Testosterone, which stimulates the development of male sexual characteristics (such as facial and chest hair) and is produced in the testes

  • Oestrogen, which stimulates the development of female sexual characteristics (such as breasts and widening hips) and is produced in the ovaries

  • Oxytocin is produced in the hypothalamus. Women typically release it in larger amounts than men; it stimulates labour and breast-feeding in mothers, as well as bonding behaviour in both sexes

Research which investigates chromosomes and hormones

• Van Goozen et al. (1995) found that transgender women (male-to-female) who were given oestrogen treatment showed decreases in aggression and visuospatial skills, while transgender men (female-to-male) treated with testosterone showed the opposite effects 

• Deady et al. (2006) conducted a correlational study in which they measured 27 young women’s testosterone levels, gave them the Bem Sex-role Inventory with extra questions about their mothering intentions and ambition to have children and found that high testosterone levels correlated with a low desire for children

Link to Issues & Debates: 

To identify all behaviour differences between males and females as being a result of their different chromosomes and hormones is biological determinism. This refers to the idea that all human behaviour is innate and it ignores the role of the environment, culture and socialisation in gendered behaviour. The idea that all human behaviour is innate is a form of hard determinism that views biological sex as directly linked and something over which the individual has no control.