Indel segregating within introns in the chicken genome are positively correlated with the recombination rates.

Insertions and deletions (Indel) are important sources of genetic diversity and phenotypic divergence. Many factors such as mutation, recombination, selection and genetic drift can jointly affect the indel distribution across the genome. Studies of the relationship between recombination and indel density can, to a certain extent, reflect the selective constrain on indel. Based on the improved genetic map, genome sequence assembly and the partial (0.25X) shotgun sequencing of three breeds of domestic chicken, we calculated the recombination rates and the indel density segregating within introns and intergenic for 4 Mb windows (n = 210). Regression analyses demonstrated that recombination rates are significantly correlated with intron indel density, but not with the intergenic indel density. After adjusted regional effect, the significant trend was remained. This implies that selection is an important factor to influence the indel distribution within introns in chicken genome. By contrast, the intergenic indel seem to be neutral. Since the intron indel density on Z chromosome is less than half of that on autosomes, we preliminarily deduced that genetic hitchhiking might be more important than background selection in producing the observed correlation. As these two processes are not mutually exclusive, it is most likely that both contribute somewhat to the observed pattern. In result similar to previous study, we also found SNP density is highly correlated with indel density. Based on this characteristic, a hypothesis suggested that there are common effects of mutation and/or selection on the occurrence of indel and point mutations. This hypothesis can not explain our observations.