Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, 50 Ngamwongwan, Chatuchak, Bangkok, 10900, Thailand.
Special Research Unit for Wildlife Genomics (SRUWG), Department of Forest Biology, Faculty of Forestry, Kasetsart University, 50 Ngamwongwan, Chatuchak, Bangkok, 10900, Thailand.
Chromosome Res. 2020 Jun;28(2):209-228. doi: 10.1007/s10577-020-09631-4. Epub 2020 May 1.
Sex chromosomes in some amniotes share linkage homologies with distantly related taxa in regions orthologous to squamate reptile chromosome 2 (SR2) and the snake W sex chromosome. Thus, the SR2 and W chromosomes may formerly have been part of a larger ancestral amniote super-sex chromosome. Comparison of various sex chromosomal linkage homologies in Toxicofera with those in other amniotes offers an excellent model to assess key cytological differences, to understand the mechanisms of amniote sex chromosome evolution in each lineage and the existence of an ancestral amniote super-sex chromosome. Chromosome maps of four species of Toxicofera were constructed using bacterial artificial chromosomes (BACs) derived from chicken and zebra finch libraries containing amniote sex chromosomal linkages. Different macrochromosome linkage homologies were highly conserved among Toxicofera, and at least two BACs (CH261-125F1 and CH261-40D6) showed partial homology with sex chromosomes of amniotes associated with SR2, which supports the hypothesis of an ancestral super-sex chromosome with overlaps of partial linkage homologies. The present data also suggest a possible multiple fission mechanism of an ancestral super-sex chromosome, which resulted in further development of various sex chromosomal linkages of Toxicofera based on particular properties that favored the role of sex chromosomes.
一些羊膜动物的性染色体与远距离相关的分类群在与蜥蜴目动物染色体 2（SR2）和蛇 W 性染色体同源的区域共享连锁同线性。因此，SR2 和 W 染色体可能曾经是更大的祖先羊膜动物超级性染色体的一部分。比较 Toxicofera 中的各种性染色体连锁同线性与其他羊膜动物的同线性，可以很好地评估关键的细胞学差异，了解每个谱系中羊膜动物性染色体进化的机制以及祖先羊膜动物超级性染色体的存在。使用来自鸡和斑马雀文库的细菌人工染色体（BAC）构建了四种 Toxicofera 物种的染色体图谱，这些文库包含了与 SR2 相关的羊膜动物性染色体连锁。Toxicofera 之间的不同宏观染色体连锁同线性高度保守，至少有两个 BAC（CH261-125F1 和 CH261-40D6）与与 SR2 相关的羊膜动物的性染色体具有部分同源性，这支持了祖先超级性染色体具有部分连锁同线性重叠的假说。目前的数据还表明，祖先超级性染色体可能经历了多次分裂机制，这导致了 Toxicofera 的各种性染色体连锁的进一步发展，这是基于有利于性染色体作用的特定特性。
