Generation of a linkage map for the hybridising toads Bombina bombina and B. variegata. Bombina linkage map

This study provides a dense linkage map for the hybridising toads Bombina bombina and B. variegata. These anciently diverged toads with large genomes (7.8 Gbp) hybridise freely wherever their distribution ranges adjoin in Central Europe. The linkage map facilitates the genomic analysis of natural hybrids and of patterns of introgression. A draft genome of a B. v. variegata male was assembled from Illumina short reads and molecular baits were designed for 5000 target loci. Enriched genomic libraries for 162 F2 offspring of a B. bombina x B. variegata cross were sequenced and and the taxon of origin was inferred for the 324 F2 haplotypes at each target locus. The linkage map contains 12 linkage groups corresponding to the 12 Bombina chromosomes. It also identifies males as the heterogametic sex in these taxa with homomorphic sex chromosomes and locates the sex-determining region within 7 cM of LG5 (homologous to Xenopus tropicalis chromosome 5)

本研究构建了适用于杂交铃蟾（Bombina bombina与B. variegata）的高密度连锁图谱（linkage map）。这两个经历了长期分化的铃蟾物种拥有庞大的基因组（7.8 Gbp），在中欧分布区接壤的区域可自由杂交。该连锁图谱可为自然杂交种群的基因组分析以及基因渐渗（introgression）模式研究提供助力。研究人员基于Illumina短读长测序（Illumina short reads）数据，组装得到一只B. v. variegata雄性个体的草图基因组，并针对5000个靶标位点（target loci）设计了分子诱饵探针（molecular baits）。研究对162只B. bombina与B. variegata杂交产生的F2后代（F2 offspring）的富集基因组文库（genomic libraries）进行了测序，并为每个靶标位点的324个F2单倍型（haplotypes）推断了其类群起源。该连锁图谱包含12个连锁群（linkage groups），与铃蟾属物种的12条染色体一一对应。此外，本研究明确了该类群中雄性为异配性别（heterogametic sex），且其性染色体为同形性染色体（homomorphic sex chromosomes），并将性别决定区域（sex-determining region）定位在LG5（与热带爪蟾Xenopus tropicalis染色体5同源）7 cM范围内。