Nature Genetics Advance Online Publication Avian W and Mammalian Y Chromosomes Convergently Retained Dosage-sensitive Regulators-猫眼课题宝

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D. W. Bellott;H. Skaletsky;Ting-Jan Cho;L. Brown;Devin P. Locke;Nancy F. Chen;S. Galkina;Tatyana Pyntikova;Natalia Koutseva;Tina Graves;Colin L. Kremitzki;W. Warren;A. Clark;E. Gaginskaya;R. Wilson;D. Page

在鸟类和哺乳动物中，雄性和雌性之间有一对染色体不同。在鸟类中，雌性为ZW，雄性为ZZ;在哺乳动物中，雌性为XX，雄性为XY。鸟类和哺乳动物的性染色体并不是直联的：在鸟类中与性别连锁的基因在哺乳动物中是常染色体的，反之亦然1-3。鸡性连锁基因的直向同源物在人类常染色体5、9和18上发现，而人类性连锁基因的直向同源物在鸡常染色体1和4上发现（参考文献10）。第1-4段）。来自鸟类和哺乳动物的性连锁基因的直系同源物在外群物种（如鱼类）的单独常染色体上被发现，这表明鸟类和哺乳动物的性染色体是独立进化的，它们曾经是共同祖先中的普通常染色体。虽然鸟类的ZW性染色体是哺乳动物XY对在性别上的镜像，但这两对染色体遵循平行的进化轨迹。在每个谱系中，一系列事件，最有可能是性别特异性（W或Y）染色体的倒位，抑制了性染色体之间的交换，导致进化层5-7的形成。在没有交换的情况下，性别特异性的W和Y染色体从它们的对应物Z和X染色体中分离出来。Z和X染色体保留了祖先常染色体4，8上存在的98%的基因。与此相反，性别特异性的W和Y染色体成为遗传衰变9。很少有祖先基因保留在哺乳动物的Y染色体上;负鼠的Y染色体是最保守的，保留了4-5%的祖先基因，而小鼠的Y染色体上的衰变更严重，只有1%的祖先基因保留下来。Z和W染色体之间的分歧程度在鸟类中差异很大，从鸸鹋和鸵鸟-其中三分之二的Z染色体仍然与W染色体在冗长的假常染色体区域交叉-到鸡，其中Z和W染色体几乎完全分化7。目前对性别特异性染色体的生物学和进化的了解很大程度上基于几条男性特异性Y染色体10-15的参考序列。脊椎动物的性染色体通常含有扩增子序列，即具有高度核苷酸同一性的长段重复序列4，8，10 -15。解析这些序列需要一种具有非常高的准确度和精确度的方法，特别是对来自单个单倍型的大插入克隆进行测序。高质量，基于克隆的Y染色体参考序列已经确定了两个...

In birds and mammals, one pair of chromosomes differs between males and females. In birds, females are ZW and males are ZZ; in mammals, females are XX and males are XY. The sex chromosomes of birds and mammals are not orthologous: genes that are sex linked in birds are autosomal in mammals, and vice versa 1–3. The orthologs of chicken sex-linked genes are found on human autosomes 5, 9, and 18, while the orthologs of human sex-linked genes are found on chicken autosomes 1 and 4 (refs. 1–4). The orthologs of sex-linked genes from birds and mammals are found on separate autosomes in outgroup species, like fish, indicating that the sex chromosomes of birds and mammals evolved independently, from what were once ordinary auto-somes in the common ancestor 4. Although the avian ZW sex chromosomes are the mirror image of the mammalian XY pair with respect to sex, these two chromosome pairs followed parallel evolutionary trajectories. In each lineage, a series of events, most likely inversions on the sex-specific (W or Y) chromosome, suppressed crossing-over between the sex chromosomes , leading to the formation of evolutionary strata 5–7. In the absence of crossing-over, the sex-specific W and Y chromosomes diverged from their counterparts, the Z and X chromosomes. The Z and X chromosomes retained 98% of the genes that existed on the ancestral autosomes 4,8. In contrast, the sex-specific W and Y chromosomes became subject to genetic decay 9. Few ancestral genes remain on mammalian Y chromosomes; the opossum Y chromosome was among the most conservative, retaining 4–5% of ancestral genes, while decay was more severe on the mouse Y chromosome, where only 1% of ancestral genes remain 10,11. The extent of divergence between the Z and W chromosomes varies widely across birds, from emu and ostrich—where two-thirds of the Z chromosome still crosses over with the W chromosome in lengthy pseudoautosomal regions—to the chicken, where the Z and W chromosomes are almost completely differentiated 7. The current understanding of the biology and evolution of sex-specific chromosomes is largely based upon the reference sequences of several male-specific Y chromosomes 10–15. Vertebrate sex chromosomes commonly contain ampliconic sequences, long stretches of duplicated sequences that have high nucleotide identity 4,8,10–15. Resolving these sequences requires a methodology with an extraordinary level of accuracy and precision—specifically, the sequencing of large-insert clones derived from a single haplotype. High-quality, clone-based Y-chromosome reference sequences have identified two …

Nature Genetics Advance Online Publication Avian W and Mammalian Y Chromosomes Convergently Retained Dosage-sensitive Regulators

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