Microsatellite-centromere mapping in common carp through half-tetrad analysis in diploid meiogynogenetic families.

Gene-centromere (G-C) mapping provides insights into the understanding of the composition, structure, and evolution of vertebrate genomes. Common carp (Cyprinus carpio) is an important aquaculture fish and has been proposed to undertake tetraploidization. In this study, we selected 214 informative microsatellite markers across 50 linkage groups of a common carp genetic map to perform gene-centromere mapping using half-tetrad analysis. A total of 199 microsatellites were segregated under the Mendelian expectations in at least one of the three gynogenetic families and were used for G-C distance estimation. The G-C recombination frequency (y) ranged from 0 to 0.99 (0.43 on average), corresponding to a fixation index (F) of 0.57 after one generation of gynogenesis. Large y values for some loci together with significant correlation between G-C distances and genetic linkage map distances suggested the presence of high interference in common carp. Under the assumption of complete interference, 50 centromeres were localized onto corresponding linkage groups (LGs) of common carp, with G-C distances of centromere-linked markers per LG ranging from 0 to 10.3 cM (2.9 cM on average). Based on the information for centromere positions, we proposed a chromosome formula of 2n = 100 = 58 m/sm + 42 t/st with 158 chromosome arms for common carp, which was similar to a study observed by cytogenetic method. The examination of crossover distributions along 10 LGs revealed that the proportion of crossover chromatids was overall higher than that of non-crossover chromatids in gynogenetic progenies, indicating high recombination levels across most LGs. Comparative genomics analyses suggested that the chromosomes of common carp have undergone extensive rearrangement after genome duplication. This study would be valuable to elucidate the mechanism of genome evolution and integrate physical and genetic maps in common carp.