鳥(niǎo)類(lèi)和哺乳動(dòng)物有鮮明的性染色體,。在鳥(niǎo)類(lèi)中,，雄性個(gè)體有一對(duì)Z染色體,，而雌性個(gè)體有一個(gè)Z染色體和一個(gè)W染色體。在哺乳動(dòng)物中,，雄性個(gè)體的染色體是XY,，雌性是XX。人們長(zhǎng)期假設(shè),，性染色體演化涉及性特異性染色體（即W染色體和Y染色體）的巨大改變,，但兩性都有的Z染色體和X染色體只發(fā)生較小的改變,。但根據(jù)一項(xiàng)新的研究，事實(shí)并不是這樣的,。
這項(xiàng)研究報(bào)告了雞的Z染色體的序列,，并將其與已完成測(cè)序的人X染色體序列進(jìn)行了比較。Z染色體和X染色體與產(chǎn)生它們的常染色體（非性染色體）相比發(fā)生了巨大變化,。而且Z染色體和X染色體似乎是遵從收斂的演化軌跡,，包括由睪丸所表達(dá)的基因家族的獲得和放大，盡管它們是從先祖基因組的不同部分獨(dú)立形成的,。（生物谷Bioon.com）
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澳研究：鴨嘴獸的性別是由5對(duì)染色體決定
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生物谷推薦原文出處：
Nature doi:10.1038/nature09172
Convergent evolution of chicken Z and human X chromosomes by expansion and gene acquisition
Daniel W. Bellott,Helen Skaletsky,Tatyana Pyntikova,Elaine R. Mardis,Tina Graves,Colin Kremitzki,Laura G. Brown,Steve Rozen,Wesley C. Warren,Richard K. Wilson& David C. Page
In birds, as in mammals, one pair of chromosomes differs between the sexes. In birds, males are ZZ and females ZW. In mammals, males are XY and females XX. Like the mammalian XY pair, the avian ZW pair is believed to have evolved from autosomes, with most change occurring in the chromosomes found in only one sex—the W and Y chromosomes1, 2, 3, 4, 5. By contrast, the sex chromosomes found in both sexes—the Z and X chromosomes—are assumed to have diverged little from their autosomal progenitors2. Here we report findings that challenge this assumption for both the chicken Z chromosome and the human X chromosome. The chicken Z chromosome, which we sequenced essentially to completion, is less gene-dense than chicken autosomes but contains a massive tandem array containing hundreds of duplicated genes expressed in testes. A comprehensive comparison of the chicken Z chromosome with the finished sequence of the human X chromosome demonstrates that each evolved independently from different portions of the ancestral genome. Despite this independence, the chicken Z and human X chromosomes share features that distinguish them from autosomes: the acquisition and amplification of testis-expressed genes, and a low gene density resulting from an expansion of intergenic regions. These features were not present on the autosomes from which the Z and X chromosomes originated but were instead acquired during the evolution of Z and X as sex chromosomes. We conclude that the avian Z and mammalian X chromosomes followed convergent evolutionary trajectories, despite their evolving with opposite (female versus male) systems of heterogamety. More broadly, in birds and mammals, sex chromosome evolution involved not only gene loss in sex-specific chromosomes, but also marked expansion and gene acquisition in sex chromosomes common to males and females.
