Sex, or what we perceive to be maleness or femaleness, is largely about the interaction between genetics and biochemistry and the effects this has on all of the tissues of the body, including the brain. Imagine a genetically pink embryo that goes into overproduction of testosterone (as happens when a gene mutation causes adrenal hyperplasia), or a genetically blue embryo that either does not switch on its SRY gene or fails to produce enough testosterone (adrenal hypoplasia), or goes into overproduction of oestrogen, and you start to see how the interplay between genetic sex and physical
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