Department of Human Genetics, Emory University School of Medicine, Atlanta, GA, 30322, USA.
Chromosome Res. 2010 Jul;18(5):543-53. doi: 10.1007/s10577-010-9134-y. Epub 2010 Jun 10.
A hallmark feature of the male-specific region of the human Y chromosome is the presence of large and near-identical palindromes. These palindromes are maintained in a state of near identity via gene conversion between the arms of the palindrome, and both neutral and selection-based theories have been proposed to explain their enrichment on the human Y and X chromosomes. While those proposed theories would be applicable to sex chromosomes in other species, it has not been established whether near-identical palindromes are a common feature of sex chromosomes in a broader range of taxa, including other tetrapods. Here, we report the genomic sequencing and features of a 279-kb region of the non-recombining portion of the W chromosome spanning the CHD1W locus in a New World sparrow, the white-throated sparrow (Zonotrichia albicollis), and the corresponding region on the Z chromosome. As has been observed for other Y and W chromosomes, we detected a high repetitive element content (51%) and low gene content on the white-throated sparrow W chromosome. In addition, we identified a 22-kb near-identical (>99%) palindrome on the W chromosome that flanks the 5' end of the CHD1W gene. Signatures of gene conversion were readily detected between the arms of this palindrome, as was the presence of this palindrome in other New World sparrows and blackbirds. Near-identical palindromes are therefore present on the avian W chromosome and may persist due to the same forces proposed for the enrichment of these elements on the human sex chromosomes.
人类 Y 染色体的男性特定位点的一个显著特征是存在大型且近乎相同的回文序列。这些回文序列通过回文臂之间的基因转换保持近乎相同的状态，并且已经提出了中性和基于选择的理论来解释它们在人类 Y 和 X 染色体上的富集。虽然这些提出的理论适用于其他物种的性染色体，但尚未确定近乎相同的回文序列是否是更广泛的分类群（包括其他四足动物）性染色体的常见特征。在这里，我们报告了非重组部分的 W 染色体的 279-kb 区域的基因组测序和特征，该区域跨越了新大陆雀、白喉雀（Zonotrichia albicollis）的 CHD1W 基因座，以及 Z 染色体上的相应区域。与其他 Y 和 W 染色体一样，我们在白喉雀的 W 染色体上检测到了高重复元件含量（51%）和低基因含量。此外，我们在 CHD1W 基因 5'端侧翼发现了一个 22-kb 的近乎相同（>99%）的回文序列。很容易在这个回文序列的臂之间检测到基因转换的特征，并且在其他新大陆雀和黑鸟中也存在这个回文序列。因此，近乎相同的回文序列存在于鸟类的 W 染色体上，并且可能由于同样的力量而得以保留，这些力量促进了这些元素在人类性染色体上的富集。
