AO1

• Humans have 23 pairs of chromosomes, each pair carrying genes that control different characteristics
• Biological sex is determined by the sex chromosome X and Y
• Chromosomes play a crucial role in determining biological sex, which in turn can influence gender identity and roles in psychological contexts
• Females typically have two X chromosomes (XX), while males have one X and one Y chromosome (XY) - the presence or absence of the Y chromosome is critical in the determination of biological sex
• If the sperm carries the Y chromosome, the gonads develop into testes - testes produce male hormones (androgens), leading to the development of male secondary sexual characteristics
• In the absence of the Y chromosome, the default development pathway leads to the formation of ovaries and female characteristics
• To see the effects of nature and nurture in gender we can look at atypical chromosome patterns
• Two atypical chromosome patterns are Klinefelter's syndrome and Turner's syndrome
• Klinefelters syndrome - extra X chromosome (XXY)
• Klinefelters is caused by a complex fault in the cell division of one of the parent's sex cells
• Klinefelter's physical characteristics

  Small testes, infertile, no body hair growth at puberty, femenine breasts and poor muscle development
• Klinefelter's social characteristics

  Poor language skills, shyness, and difficulties with social interaction
• Girls with Tuner's syndrome are designated XO
• Turner's physical characteristics

  Short stature, no taller than 4'8", webbed neck, ovaries fail to develop, unable to concieve
• However, since the uterus is normal, in-vitro fertilisation using donorova is possible
• At puberty, breasts do not develop, pubic hair does not appear, and mensturation does not occur but can be treated by giving oestrogen
• Turner's social characteristics

  Lower than average mathematical skills, higher than average verbal ability, very femenine in their behaviour but difficulty in social adjustment at school