The gene SRY (sex determining region Y) on the Y chromosome causes testes to develop in an XY embryo. These produce androgens (male sex hormones) which cause the embryo to become male. Without them, the embryo develops into a female.
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What is oestrogen? It is a female hormone that determines female sexual characteristics and the menstrual cycle. It also causes some women to experience increased emotionality and irritability during the menstrual cycle, referred to as PMS.
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The influence of chromosomes is supported by the case of David Reimer who lost his penis in an accident during a circumcision procedure. His parents and Dr Money decided to raise him as a girl called Brenda without her knowledge.
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In a double blind study, 43 males were give a weekly injection of testosterone or a placebo and after ten weeks, there were no significant differences in aggression between the two groups.
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Feminist critiques claim that PMS is a social construction, a way of privileging certain groups over others. The medicalisation of women's lives and the dismissal of their emotions, especially anger. It stereotypes female experience and emotion.
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There are also strong environmental influences such as family, culture and social norms. The sex of the baby affects how they are treated and so it may be impossible to separate nature and nurture.
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What is Klinefelter's syndrome? A syndrome affecting males in which the genotype has an extra X chromosome (XXY).
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Psychological characteristics: poorly developed language and reading ability. Passive, shy and lack interest in sexual activity. Tend not to respond well to stress and may display problems with memory and problem solving.
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Physical characteristics: no menstrual cycle, ovaries don't develop = sterile, no breast development, low set ears and webbed neck. Physically immature.
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Studying such syndromes gives us a greater insight by comparison of typical and atypical chromosome patterns. We can learn more about the effects of chromosomes and testing can be made more reliable, earlier diagnosis and treatment.
