Cosegregation of recombinant chromatids maintains genome-wide heterozygosity in an asexual nematode
Caroline Blanc, Nathanaëlle Saclier, Ehouarn Le Faou, Lucas Marie‐Orleach, Eva Wenger, Célian Diblasi, Sylvain Glémin, Nicolas Galtier, Marie Delattre
Abstract
In asexual animals, female meiosis is modified to produce diploid oocytes. If meiosis still involves recombination, this is expected to lead to a rapid loss of heterozygosity, with adverse effects on fitness. Many asexuals, however, have a heterozygous genome, the underlying mechanisms being most often unknown. Cytological and population genomic analyses in the nematode Mesorhabditis belari revealed another case of recombining asexual being highly heterozygous genome-wide. We demonstrated that heterozygosity is maintained despite recombination because the recombinant chromatids of each chromosome pair cosegregate during the unique meiotic division. A theoretical model confirmed that this segregation bias is necessary to account for the observed pattern and likely to evolve under a wide range of conditions. Our study uncovers an unexpected type of non-Mendelian genetic inheritance involving cosegregation of recombinant chromatids.