atypical sex chromosomes and hormones

• Klinefelter's syndrome

  • Affects between 1 in 500 and 1 in 1000 people
  • Individuals have an additional X chromosome, resulting in XXY sex chromosome structure
  • Around two-thirds of people with Klinefelter's syndrome are not aware of it
  • Diagnosis often comes about accidentally via a medical examination for some unrelated condition
• Turner's syndrome

  • Affects approximately 1 in 5000 biological females
  • Caused by an absence of one of the two allotted X chromosomes, resulting in 45 chromosomes rather than the usual 46
• klinefelter’s syndrome 


  a syndrome affecting males in which an individuals genotype has an extra X chromosome in addition to the normal X and Y

  sex chromosome structure is then XXY
• physical characteristics of klinefelter’s syndrome

  reduced body hair compared to a normal male

  long gangly limbs

  underdeveloped genitals

  problems with coordination

  general clumsiness

  tall thin physique
• psychological characteristics of klinefelter’s syndrome

  poorly developed language skills and reading ability

  tend to be passive

  shy

  lack interest in sexual activity

  tend not to respond well in stressful situations

  may exhibit problems with memory and problem solving (executive functions)
• turner’s syndrome 


  a chromosomal disorder in which women only have one X chromosome causing developmental abnormalities and infertility

  affected individuals have 45 chromosomes instead of 46
• physical characteristics of turner’s syndrome

  no menstrual cycle - ovaries fail to develop and they are sterile

  low set ears

  webbed neck

  hips not bigger than waist

  broad shield chest

  physically immature

  tend to retain the appearance of pre pubescent girls
• psychological characteristics of turner’s syndrome

  higher than average reading ability

  performance on spatial, visual memory and mathematics tasks is lower than normal

  socially immature

  have trouble relating to peers

  experience difficulty fitting in
• TICK by comparing people who have these conditions with chromosome-typical individuals and ones who don't, it becomes possible to see psychological and behavioural differences between the groups

  • can be logically inferred that these differences have a biological basis and are a direct result of the abnormal chromosomal structure = suggests that innate 'nature' influences have a powerful effect on psychology and behaviour
• X may be that environmental and social influences are more responsible for the behavioral differences

  eg. social immaturity observed in females with turner's syndrome may arise from the fact that they are treated immaturely by the people around them

  • therefore it is wrong to assume that observed psychological and behavioural differences are due to nature
• X lack of generalisability from atypical individuals to the wider population
• X individuals who look different due to their unusual chromosomes are unlikely to be treated in the same way as their peers - can make it harder to assess the contribution of nature and nurture in behavioural and psychological differences
• X based on stereotypical assumptions of what constitutes as 'normal' behaviour for men and women
• treating klinefelter's syndrome - testosterone replacement therapy

  can help increase hormone levels towards a normal range

  can produce bigger muscles, deepen voice, and stimulate hair growth
• treating turner's syndrome - growth hormone injections

  injections begin in early childhood and may increase final adult height by a few inches
• treating turner's syndrome - oestrogen replacement therapy


  started at the time of normal puberty to help start development

  oestrogen and progesterone given a little later to begin a monthly period, which is necessary to keep the womb healthy