大多数有性生殖的物种都能保持两性数量的大致平衡，这一直令科学家迷惑不解。美国研究人员近日通过对果蝇染色体的研究，得出结论认为，此现象可能是由特定的基因所致。这一发现有助于科学家深入理解基因组的进化和新物种的形成。相关论文发表在11月份的《公共科学图书馆·生物学》（PLoS Biology）上。
此次研究由美国埃默里大学（Emory University）的进化遗传学家Tao Yun领导完成。研究人员比较了两种雄性果蝇的DNA，其中一种后代90%都是雌性，另一种后代的两性数目大致相等。研究人员发现，X染色体上含有名为Dox基因的雄性果蝇产生的含X染色体的精子会破坏含Y染色体精子的活性，从而导致更多的雌性后代出现。通过遗传手段使果蝇缺失Dox基因后，含Y染色体精子的活性会恢复正常，所产生的后代两性比例大致相当。
在另外一个独立的实验中，研究人员在另一个染色体上发现了一个名为Nmy的基因，它能够抑制Dox的活性。含有这两种基因的果蝇能产生两性数量相当的后代，而缺乏Nmy就会导致产生更多的雌性后代。
Tao表示，虽然尚不清楚这两种基因是否在其他物种中也存在，但这一发现有助于解释减数分裂性染色体失活这一普遍存在的现象。有可能正是通过阻碍Dox的作用，物种保持了两性数量的平衡。
美国罗切斯特大学的进化遗传学家Daven Presgraves说，这一发现是开创性的。它提升了这样一种可能性，即Dox和Nmy促进了X染色体的遗传变异，而有可能就是这种变异导致了新物种的产生。他说：“新物种的产生有可能就是自私基因和它们的抑制者相互‘角力’时，偶然出现的副产品。”
原始出处:
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
