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Q J Med 2004; 97: 381-382
QJM vol. 97 no. 6 © Association of Physicians 2004; all rights reserved.

Biologic

How does X mark the spot?

Colin Berry

The first 10% of the full text of this article appears below.

Mammals can be distinguished as male and female by their differing number of X and Y chromosomes. Although sex determination may be dependent on a number of different mechanisms, there has to be a way of avoiding a double dose of active X genes in those with two Xs. This is achieved by a number of differing mechanisms in different groups; in XX C. elegans, genes on both X chromosomes are expressed, but each X is repressed by half, relative to the output of a single male X (Xm). In Drosophila, the solution is . . . [Full Text of this Article]


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