SIMPLE SEQUENCE REPEATS AS A SOURCE OF QUANTITATIVE GENETIC-VARIATION

Mast traits in biological populations appear to be under stabilizing s election which acts to eliminate quantitative genetic variation Yet, v irtually all measured traits in biological populations continue to sho w significant quantitative genetic variation. The paradox can be resol ved by postulating the existence of an abundant, though unspecified, s ource of mutations that has quantitative effects on phenotype, bid noe s not reduce fitness. Does such a source actually exist? We propose th at it noes, In the form of repeat-number variation in SSRs (simple seq uence repeats, of which the triplet repeats of human neurodegenerative diseases are a special case). Viewing SSRs as a major source of quant itative mutation has broad implications for understanding molecular pr ocesses of evolutionary adaptation, including the evolutionary control of the mutation process itself.