The molecular mechanism underlying the "rare allele phenomenon" in a subspecific hybrid zone of the California field mouse, Peromyscus californicus.

Natural hybrid zones are known to have unusually high levels of novel or otherwise rare electrophoretic variants (the "rare allele phenomenon"). These variant alleles are most likely the result either of high levels of unique mutations in hybrids or of intragenic recombination between divergent alleles from the parental populations. This study uses DNA sequence comparisons to determine which process has produced a rare allele of the 6-phosphogluconate dehydrogenase (6-PGD) gene in a subspecific hybrid zone of the California field mouse (Peromyscus californicus). About 70% of the coding sequence of 6-PGD was cloned and sequenced from three alleles, including two widespread alleles and one rare allele unique to hybrid populations. Sequence comparisons among the three alleles reveal no patterns that would indicate that the variant was formed by intragenic recombination. Instead, the unique allele of 6-PGD studied seems to have developed by the accumulation of base substitutions, which supports the hypothesis of increased mutation rates in hybrids.