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Letters to Nature
Nature 209, 429-431 (22 January 1966) | doi:10.1038/209429b0
Evolution of Over-dominance during the Initial Spread of New Alleles
S. K. JAIN
- Department of Agronomy, University of California, Davis.
Abstract
Bodmer and Parsons1–3 have discussed a model for the initial increase in the frequency of newly arising, favourable mutations in a large undivided population and under different mating systems. They argued that over-dominance (higher fitness of heterozygotes over the homozygotes) has evolved in out breeding species during this process as follows: (1) a new allele, say A1, at locus A1–A2 occurs principally in the heterozygotes when it is initially at a low frequency in the population; (2) selection favouring heterozygotes allows a rapid rate of increase in frequency of A1; (3) hence, the modifiers that primarily enhance the fitness of A1A2 particularly when linked, would themselves increase rapidly in frequency and accumulate to form the linked gene complexes; (4) such gene combinations would exhibit so-called segmental (or associative4) over-dominance maintaining a balanced polymorphism.
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