Intragenic Recombination as a Source of Population Genetic Variability

Intragenic recombination, between alternative nucleotide sequences within single-gene loci, generates new allelic sequences under certain conditions. In particular, certain minimum levels of variation must already exist in the population, and at the loci, in question. This process differs qualitatively from recombination between separate loci in populations, since it causes the production of new gene products, with potentially novel properties, rather than new genotypic combinations of unaltered gene products. Deterministic models of intragenic recombination in populations, assuming several alternative mechanisms for the operation of the process, are presented. Their quantitative properties are studied by explicit solution or by iteration in a computer. These calculations show that, for reciprocal and nonreciprocal mechanisms alike, intragenic recombination can produce new alleles at rates several orders of magnitude above observed rates of "standard" mutational processes. In effect, as long as the minimum amount of variability is maintained at a locus, intragenic recombination will generate more variability by assembling all possible sequence combinations of those variations present. It will thus act as a high frequency locus-specific mutation process, and in some ways will imitate "directed mutation." The variants thus produced may have different fates depending on the population size, breeding system, selective regime, etc. Present methods for electrophoretic surveying of enzyme-level genetic variation in populations may provide a convenient means of studying the actual operation of intragenic recombination in the wild.