Centromere-linkage in the turbot (Scophthalmus maximus) through half-tetrad analysis in diploid meiogynogenetics

Seventy nine microsatellite markers selected across all linkage groups (LG) from a previous turbot genetic map were studied in a diploid meiogynogenetic family for centromere mapping using half-tetrad analysis. Significant deviations from Mendelian segregation were observed at 25% loci analyzed. The clustering of distorted loci at specific LGs, suggested the existence of genes of different deleterious effects. The lack of Mendelian segregation distortion at 1 day and 10 days post-hatching larvae at these loci precluded an explanation based on aberrant meiotic segregation. Heterozygote frequency distribution in gynogenetic offspring showed close to 50% values above 0.667, which suggested high chiasma interference in turbot. Complete interference appeared as the best fitting function when estimating centromere position. However, Kosambi and Haldane functions performed better at specific LGs as a consequence of the variable crossover pattern of centromere-distant markers among LG. Great concordance between half-tetrad data and the positions previously reported in the turbot map was observed. Most centromeres were localized with an error around or below 5 cM and closely linked markers exist now in 8 LGs. Centromere location was mostly in accordance with previous karyotypic information.