Atypical sex chromosome patterns

• Atypical sex chromosome patterns

  • Any sex chromosome pattern that deviates from the usual XX/XY formation and which tends to be associated with a distinct pattern of physical and psychological symptoms.
• Examples of atypical sex chromosome combinations

  • Klinefelter’s syndrome
  • Turner’s syndrome
• Klinefelter’s syndrome

  • Affects 1 in 600 males
  • Individuals who have this condition are biologically male, with the anatomical appearance of a male and have an additional X chromosome.
  • Sex chromosome structure is XXY
• Sex chromosome structure in Klinefelter’s syndrome


  XXY
• Physical characteristics of Klinefelter’s syndrome

  • Reduced body hair
  • Breast development (gynaecomastia) at puberty
  • Long gangly limbs
  • Underdeveloped genital
  • Problems with co-ordination and general clumsiness
  • XXY men’s are susceptible to health problems commonly found in females. e.g breast cancer
• Psychological characteristics of Klinefelter’s syndrome

  • Poorly developed language skills and reading ability
  • Tend to be passive, shy and lack interest in sexual activity
  • Don’t respond well to stressful situations.
  • Problems with executive functions such as memory and problem solving.
• Turner’s syndrome

  • 1 in 5000 biological females have Turner’s syndrome
  • Created by the absence of 2 allotted X chromosomes this is referred to as XO
  • This means affected individuals have 45 chromosomes instead of 46 chromosomes.
• Physical characteristics of Turner’s syndrome

  • Do not have a menstrual cycle (amenorrhoea) their ovaries do not develop so they are infertile.
  • Do not develop breast at puberty, instead they have a broad ‘shield’ chest
  • Low set ears
  • Webbed neck
  • High hip to waist ratio
  • Retain the appearance of prepubescent girls
• Psychological characteristics of Turner’s syndrome

  • Higher than average reading ability
  • Performance on spatial, visual memory and mathematical tasks is lower than average
  • Socially immature- have trouble relating to their peers and find it difficult to fit in
• Treatment of Klinefelter’s syndrome

  • Testosterone replacement therapy, helps to increase hormone levels to normal range.
  • Can help to produce bigger muscles, deepen the voice and stimulate hair growth
  • Fertility treatment
• Treatment of Turner’s syndrome

  • Growth hormone injections are beneficial for some in early childhood, in order to increase adult height.
  • Oestrogen replacement therapy started at puberty to start breast development
  • Oestrogen and progesterone given later to begin menstruation to keep the womb healthy.
• How does the atypical sex chromosome theory contribute to nature-nurture debate?

  • By comparing them to those with typical sex chromosome patterns, we can see the psychological and behavioural differences in the 2 groups.
  • For example, people with Turner’s syndrome have higher verbal ability and talk more than typical girls.
  • Therefore we could say these differences are due to biology and a direct result of abnormal chromosomal structure, suggested that nature influences behaviour.
• Nurture influence on atypical sex chromosomes

  • It may be that psychological and behavioural differences seen in Turner’s syndrome is due environmental and social influences, not biology.
  • For example, it might be that those with Turner’s syndrome are socially immature as they have been treated immaturely by those around them e.g parents, peers as they may react to the pre-pubescent appearance in a way that encourages immaturity and affects performance at school, causing developmental problems to be identified.
  • There we cannot assume that the differences are due to nature.
• Real world application to atypical sex chromosomes

  • Continued research will lead to earlier and more accurate diagnosis and more positive outcomes for individuals.
  • An Australian study of 87 people with Klinefelter’s syndrome showed that those who has been identified and treated from a young age had significant benefits compared to those diagnosed in adulthood.
  • Awareness of atypical chromosome patterns have helped improved quality of life for individuals diagnosed with Klinefelter’s and Turner’s syndrome.
• Sampling issues

  • In order to identify characteristics of XXY and XO individuals, it is necessary to identify a large sample and build a database. We can then get an idea of the range of characteristics from mild to severe. However only a third of people with Klinefelter’s syndrome have been diagnosed and therefore been the subject of research which may distort findings.
  • Boada et al study follows children from birth and has produced a more accurate picture many do not report cognitive or psychological problems and many are highly successful in their academic and personal lives.
• Why is the fact that many people are unaware they have a condition a problem?

  • 2 thirds of people with Klinefelter’s are unaware of it.
  • This can be seen in a positive light as it avoids a self-fulfilling prophecy.
  • Therefore knowing you have the syndrome creates self-expectations of what your capabilities are.
• Contradictory evidence-Why is it good to know that you have the disorder?

  • Early knowledge of the syndrome may help people understand why they appear and act different from other children of the same age.
  • This means that the child doesn’t fell their physical and psychological differences are their fault and can seek early access to medical and psychological support.