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| Modern Genetic Analysis Chapter 7. Gene Mutations The Molecular Basis of Mutation Figure 7-20. Expansion of the CGG triplet in the FMR-1 gene seen in the fragile X syndrome. Normal persons have from 6 to 54 copies of the CGG repeat, whereas those from susceptible families display an increase (premutation) in the number of repeats: normally transmitting males (NTMs) and their daughters are phenotypically normal but display 50 to 200 copies of the CGG triplet; the number of repeats expands to some 200 to 1300 in persons showing full symptoms of the disease.

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