Month: October 2014

The role and importance of epistasis (non-additive interactions between alleles) in shaping genetic variation, and its effects on fitness have been the focus of much debate. Russell et al. recently investigated the genomic footprint of epistatic fitness effects. Starting from two sets of 8 highly inbred Drosophila melanogaster strains, they created 4 panels of 400 recombinant inbred lines. Then, they investigated non independent allelic segregation of pairs of unlinked loci (i.e. on different chromosomes; figure 1 a and c). Indeed, it is expected that unfavourable allelic combinations will be under-represented in a the population. This deviation from Mendelian proportions was refereed as genotype ratio distortion (GDP). 22 pairs of epistatically interacting alleles could be identified. Many of the incompatible alleles are present in more than one founder strain, suggesting that they were segregating in natural populations. They estimated that any pairwise combination of founder strains has, on average, 1.15 pairs of epistatically interacting alleles . They performed experimental crosses in order to investigate two incompatibilities in more details. They discovered that the negative interaction is caused by the minor alleles at each locus in both cases (Figure 1 b, d). Interestingly, both involved a reduction in male fertility (with respectively …