Reversed sex-biased mutation rates for indels and base substitutions in Drosophila melanogaster

Mutation rate heterogeneity between males and females is well-documented and frequently attributed to different numbers of germline cell divisions. In Drosophila melanogaster the number of germline cell divisions are similar, but single nucleotide variants (SNVs) still have higher mutation rates, suggesting sex-specific differences in replication or DNA repair. Since, the influence of (linked) selection may also have affected this pattern, we studied the sex-specific mutation patterns in mutation accumulation lines, which minimizes the influence of purifying selection. To obtain a sufficiently large number of independent mutations, we used mismatch-repair deficient D. melanogaster lines. We confirm the higher SNV mutation rate in males, but find a higher indel rate in females. Since the mismatch repair mostly affects mutations during DNA replication and only young females were used in our experiment, we consider mutations in quiescent cells an unlikely explanation for the higher indel mutation rate in females. The differences in SNV and indel mutation rates explain why D. melanogaster X-chromosomes have longer microsatellites than autosomes.