Fridolfsson A K, Cheng H, Copeland N G, Jenkins N A, Liu H C, Raudsepp T, Woodage T, Chowdhary B, Halverson J, Ellegren H
Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Biomedical Center, Box 597, S-751 24 Uppsala, Sweden.
Proc Natl Acad Sci U S A. 1998 Jul 7;95(14):8147-52. doi: 10.1073/pnas.95.14.8147.
Among the mechanisms whereby sex is determined in animals, chromosomal sex determination is found in a wide variety of distant taxa. The widespread but not ubiquitous occurrence, not even within lineages, of chromosomal sex determination suggests that sex chromosomes have evolved independently several times during animal radiation, but firm evidence for this is lacking. The most favored model for this process is gradual differentiation of ancestral pairs of autosomes. As known for mammals, sex chromosomes may have a very ancient origin, and it has even been speculated that the sex chromosomes of mammals and birds would share a common chromosomal ancestry. In this study we showed that the two genes, ATP5A1 and CHD1, so far assigned to the female-specific W chromosome of birds both exist in a very closely related copy on the Z chromosome but are not pseudoautosomal. This indicates a common ancestry of the two sex chromosomes, consistent with the evolution from a pair of autosomes. Comparative mapping demonstrates, however, that ATP5A1 and CHD1 are not sex-linked among eutherian mammals; this is also not the case for the majority of other genes so far assigned to the avian Z chromosome. Our results suggest that the evolution of sex chromosomes has occurred independently in mammals and birds.
在动物性别决定的机制中，染色体性别决定存在于多种远缘分类群中。染色体性别决定在动物类群中广泛存在但并非普遍存在，甚至在同一谱系内也不是普遍存在，这表明性染色体在动物辐射演化过程中曾多次独立进化，但目前尚缺乏确凿证据。关于这一过程最受青睐的模型是祖先常染色体对的逐渐分化。正如哺乳动物的情况一样，性染色体可能起源非常古老，甚至有人推测哺乳动物和鸟类的性染色体有共同的染色体祖先。在本研究中，我们发现，迄今为止被认为是鸟类雌性特异性W染色体上的两个基因ATP5A1和CHD1，在Z染色体上都存在非常相似的拷贝，但并非拟常染色体基因。这表明两条性染色体有共同的祖先，与由一对常染色体进化而来的观点一致。然而，比较图谱分析表明，ATP5A1和CHD1在真兽类哺乳动物中并非性连锁基因；到目前为止，大多数其他被认为位于鸟类Z染色体上的基因也是如此。我们的研究结果表明，性染色体在哺乳动物和鸟类中是独立进化的。
