What makes a man?

In a seven-week-old embryo, the sex glands and organs of males and females appear identical. In male embryos, the testis determining factor gene, called SRY, is then switched on. This 'male gene', found on the Y-chromosome, triggers male development in all mammals and causes the testes and male external genitals to start to grow. In a female embryo, there is no Y-chromosome and no SRY gene, allowing the ovaries and female external genitals to develop. Other genes are also involved in sex determination.

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This model of a 12-week-old fetus is on display in the Who Am I? gallery.


Principal Funder:

Wellcome trust

Major Sponsors:

GlaxoSmithKline life technologies