The Role of Genes and Hormones

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The Role of Genes and Hormones

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The role of genes in gender development

> Each person has 23 pairs of chromosomes in each cell of the body & these chromosomes carry hundreds of genes containing instructions about physical & behavioural characteristics (eye colour & predisposition to mental illness).

> 1 pair of chromosomes are called the sex chromosomes because they determine an individual's sex. XX chromosomes = female & XY chromosomes = male. Y carries little genetic material but does determine the sex.

> There's usually a direct link between an individual's chromosomal sex and their external & internal genitalia.

> During prenatal development all individuals start out the same (m & f embryos have external genitalia that look essentially feminine).

> When the foetus is 3 months old, if it develops as male, the testes usually produce the male hormone testosterone which causes external male genitalia to develop.

> Genetic transmission explains how individuals acquire their sex - it may also explain some aspects of gender because of the link between genes and genitalia and hormones.

The role of hormones in gender development

> Chromosomes initially determine a person's sex but most gender development is governed by hormones which are produced prenatally & in adolescence (puberty). These influence the development of genitalia & the brain (both influence gender behaviour).

Development of genitalia

> The role of hormones in gender development can be seen by studying individuals who have been exposed prenatally to abnormal hormone levels (intersex individuals).

> Normally external genitalia are in accord with genetic sex but in some cases a genetic male embryo is exposed to too little male hormone and the result is that the newborn appears externally female (AIS & Batista family).

> Genetic females may be exposed prenatally to too much male hormone & the result is ambiguous genitalia (swollen labia resembling a penis) - such girls are usually assigned girls at birth and are content with this gender.

> BERENBAUM AND BAILEY found that girls exposed prenatally to too much testosterone are often interested in male-type activities and are tomboyish, presumably due to the influence of the male hormones.

Brain development

Sex differences explained - 

> Male brains are different from female brains in…

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