A phylogeny for the principal alleles of the human phosphoglucomutase-1 locus.

The results of phosphoglucomutase-1 (PGM1) typings by starch gel electrophoresis and subtypings by isoelectric focusing are presented for a sample of Japanese. A distinction made on the basis of isoelectric focusing (termed "+" and "-") is nonrandomly associated with each of the products of the four most common electrophoretic alleles (PGM1(1), PGM1(2), PGM1(3), and PGM1(7). The isoelectric trait cosegregates with the allele; the degree of nonrandomness of the association varies from allele to allele. Thus, the four alleles become eight. On the basis of these facts plus the additive nature of the pI differences between allele products and the geographical distribution of the alleles, an allele phylogeny can be constructed. This postulates that the eight alleles may be explained by three nucleotide substitutions involving the stem allele plus four intragenic recombinations between these substitutions. The potential of intragenic recombination as a cause of mutation has been insufficiently appreciated.