Genomic changes following the reversal of a Y chromosome to an autosome in Drosophila pseudoobscura

Robertsonian translocations resulting in fusions between sex chromosomes and autosomes shape karyotype evolution by creating new sex chromosomes from autosomes. These translocations can also reverse sex chromosomes back into autosomes, which is especially intriguing given the dramatic differences between autosomes and sex chromosomes. To study the genomic events following a Y chromosome reversal, we investigated an autosome-Y translocation in Drosophila pseudoobscura. The ancestral Y chromosome fused to a small autosome (the dot chromosome) approximately 10–15 Mya. We used single molecule real-time sequencing reads to assemble the D. pseudoobscura dot chromosome, including this Y-to-dot translocation. We find that the intervening sequence between the ancestral Y and the rest of the dot chromosome is only ∼78 Kb and is not repeat-dense, suggesting that the centromere now falls outside, rather than between, the fused chromosomes. The Y-to-dot region is 100 times smaller than the D. melano...

罗伯逊易位（Robertsonian translocation）可导致性染色体与常染色体发生融合，通过将常染色体转化为新型性染色体，从而塑造核型演化的进程。这类易位还可将性染色体逆转回常染色体；鉴于常染色体与性染色体之间存在显著差异，这一现象尤为引人关注。为探究Y染色体逆转后的基因组事件，我们对伪黑腹果蝇（Drosophila pseudoobscura）中的一条常染色体-Y易位展开了研究。大约1000万至1500万年前，祖先Y染色体与一条小型常染色体（点染色体，dot chromosome）发生了融合。我们采用单分子实时测序（single molecule real-time sequencing）读长，对伪黑腹果蝇的点染色体（包含该Y-点易位区域）进行了基因组组装。我们发现，祖先Y染色体与点染色体其余区域之间的间隔序列仅约78千碱基对，且不具备高重复序列密度，这表明着丝粒（centromere）如今位于融合染色体之外，而非二者之间。该Y-点易位区域的大小仅为D. melano...对应区域的百分之一……