大多數(shù)有性生殖的物種都能保持兩性數(shù)量的大致平衡,，這一直令科學(xué)家迷惑不解。美國(guó)研究人員近日通過對(duì)果蠅染色體的研究,，得出結(jié)論認(rèn)為,，此現(xiàn)象可能是由特定的基因所致。這一發(fā)現(xiàn)有助于科學(xué)家深入理解基因組的進(jìn)化和新物種的形成,。相關(guān)論文發(fā)表在11月份的《公共科學(xué)圖書館·生物學(xué)》（PLoS Biology）上,。
此次研究由美國(guó)埃默里大學(xué)（Emory University）的進(jìn)化遺傳學(xué)家Tao Yun領(lǐng)導(dǎo)完成。研究人員比較了兩種雄性果蠅的DNA,，其中一種后代90%都是雌性,，另一種后代的兩性數(shù)目大致相等。研究人員發(fā)現(xiàn),，X染色體上含有名為Dox基因的雄性果蠅產(chǎn)生的含X染色體的精子會(huì)破壞含Y染色體精子的活性,，從而導(dǎo)致更多的雌性后代出現(xiàn)。通過遺傳手段使果蠅缺失Dox基因后,，含Y染色體精子的活性會(huì)恢復(fù)正常,，所產(chǎn)生的后代兩性比例大致相當(dāng)。
在另外一個(gè)獨(dú)立的實(shí)驗(yàn)中,，研究人員在另一個(gè)染色體上發(fā)現(xiàn)了一個(gè)名為Nmy的基因,，它能夠抑制Dox的活性。含有這兩種基因的果蠅能產(chǎn)生兩性數(shù)量相當(dāng)?shù)暮蟠?，而缺乏Nmy就會(huì)導(dǎo)致產(chǎn)生更多的雌性后代,。
Tao表示,，雖然尚不清楚這兩種基因是否在其他物種中也存在，但這一發(fā)現(xiàn)有助于解釋減數(shù)分裂性染色體失活這一普遍存在的現(xiàn)象,。有可能正是通過阻礙Dox的作用,，物種保持了兩性數(shù)量的平衡。
美國(guó)羅切斯特大學(xué)的進(jìn)化遺傳學(xué)家Daven Presgraves說,，這一發(fā)現(xiàn)是開創(chuàng)性的,。它提升了這樣一種可能性，即Dox和Nmy促進(jìn)了X染色體的遺傳變異,，而有可能就是這種變異導(dǎo)致了新物種的產(chǎn)生,。他說：“新物種的產(chǎn)生有可能就是自私基因和它們的抑制者相互‘角力’時(shí)，偶然出現(xiàn)的副產(chǎn)品,。”
原始出處:
Received: April 12, 2007; Accepted: September 17, 2007; Published: November 6, 2007
A sex-ratio Meiotic Drive System in Drosophila simulans. II: An X-linked Distorter
Yun Tao1,2*, Luciana Araripe1, Sarah B. Kingan1, Yeyan Ke1, Hailian Xiao2, Daniel L. Hartl1
1 Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America, 2 Department of Biology, Emory University, Atlanta, Georgia, United States of America
The evolution of heteromorphic sex chromosomes creates a genetic condition favoring the invasion of sex-ratio meiotic drive elements, resulting in the biased transmission of one sex chromosome over the other, in violation of Mendel's first law. The molecular mechanisms of sex-ratio meiotic drive may therefore help us to understand the evolutionary forces shaping the meiotic behavior of the sex chromosomes. Here we characterize a sex-ratio distorter on the X chromosome (Dox) in Drosophila simulans by genetic and molecular means. Intriguingly, Dox has very limited coding capacity. It evolved from another X-linked gene, which also evolved de nova. Through retrotransposition, Dox also gave rise to an autosomal suppressor, not much yang (Nmy). An RNA interference mechanism seems to be involved in the suppression of the Dox distorter by the Nmy suppressor. Double mutant males of the genotype dox; nmy are normal for both sex-ratio and spermatogenesis. We postulate that recurrent bouts of sex-ratio meiotic drive and its subsequent suppression might underlie several common features observed in the heterogametic sex, including meiotic sex chromosome inactivation and achiasmy.
英文全文：
http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050293
