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. Author manuscript; available in PMC: 2015 Feb 9.
Published in final edited form as: Bioessays. 2009 Jan;31(1):71–83. doi: 10.1002/bies.080122

Figure 2.

Figure 2

The prezygotic model of expansion of the fragile X mutation. This model assumes that an expansion of a maternal PM to an FM takes place during meiosis. The fertilised oocyte carries an FM allele. After separation from the embryo proper, the PGCs have an FM. Some alleles will contract to PMs. To explain why FMs are only transmitted through females, some selection must exist against FMs in the male germ line during spermatogenesis. In the mature testes, PM alleles predominate. In somatic cells and the female germ line, this selection does not take place. Cells with a PM are shown in green and cells with an FM are depicted in orange.