Gene conversion restores selfing in experimentally evolving populations with loss-of-function mutation.

We have discovered a new case of gene conversion restoring ability of self-fertilization in obligatory outcrossing populations. The mutation, used to transform the nematodes’ mating system from mostly self-fertilization to obligatory outcrossing, was spontaneously removed by replacing a fragment of gene with a fragment of its paralog, . This has occurred spontaneously in experimental evolution with large populations, evolving with mutation for over a hundred generations, without addition mutagens or other factors promoting mutation accumulation. A converted allele restoring hermaphrodite sperm production was detected in five experimental populations. This raises the question about stability of obligatory outcrossing populations in long-term experiments.