Ancestral polymorphism and linkage disequilibrium at the het-6 region in pseudohomothallic Neurospora tetrasperma

Abstract

In species of Neurospora, non-self recognition is mediated by at least 11 heterokaryon ( het) incompatibility loci. Previously, we identified ancient allelic variation at het-c in pseudohomothallic N. tetrasperma, which confirmed outcrossing in this species. Here, we report distinct ancestral alleles at het-6 and un-24, two closely linked genes with het incompatibility function in N. crassa. The pattern of variation at het-6 and un-24 in N. tetrasperma is similar to that observed for N. crassa, where two ancestral allele specificities exist for each locus, Oak Ridge ( het-6 OR , un-24 OR ) and Panama ( het-6 PA , un-24 PA ). Only het-6 OR / un-24 OR and het-6 PA / un-24 PA allele combinations have been observed. The absence of recombinant haplotypes ( e.g., het-6 OR / un-24 PA ) appears to derive from an ancestral chromosomal rearrangement that limits recombination. Allelic variation at het-6 and un-24 in N. tetrasperma provides further evidence of outcrossing in this predominantly selfing species and indicates that selection maintains ancient allelic diversity at het loci.