Meiotic recombination spans almost entire chromosome arms in a fully monoarmed karyotype of an African annual killifish Nothobranchius virgatus

Background During meiosis, homologous chromosomes pair to form synaptonemal complexes (SCs) and exchange genetic material through a process known as meiotic recombination. It starts with programmed DNA double-strand breaks, followed by the assembly of recombination foci on SCs. These foci mark the sites of recombination intermediates and future crossovers. Distributions of recombination foci along SCs have been studied in many eukaryotes, revealing the interplay between recombination patterns and genome evolution. However, in fish, data on recombination patterns are scarce, and, for the majority of groups, completely absent. Results We measure the positions of MLH1 foci in 3,504 SCs from 219 meiotic cells obtained from two males of an African annual killifish Nothobranchius virgatus , a representative of a genus with remarkable karyotype and genome diversity, and present a detailed statistical analysis of its recombination patterns. In contrast to the several other fish species characterised to date, recombination in both N. virgatus males occurs across almost entire chromosome arms, sharply decreasing only at (peri)centromeres and telomeres. Additionally, both individuals demonstrate interference between foci, with the minimal interfocus distance of ~​4 μm. Because the two males were derived from two different populations, we hypothesise that these properties are characteristic of the species. Our further analysis revealed significant differences between the two individuals in their SC lengths, as well as the numbers and positions of MLH1 foci. These disparities may reflect inter-individual or inter-populational variability within the species. Conclusions We provide a detailed analysis of the male meiotic recombination in two individuals of a killifish with a fully acrocentric karyotype and contribute to cytogenomic and statistical methodology for the future exploration of meiotic recombination patterns.