Coyne Jerry A, Kay Emily H, Pruett-Jones Stephen
Department of Ecology and Evolution, The University of Chicago, Chicago, IL 60637, USA.
Evolution. 2008 Jan;62(1):214-9. doi: 10.1111/j.1558-5646.2007.00254.x. Epub 2007 Nov 12.
The genetic basis of sexual dimorphisms is an intriguing problem of evolutionary genetics because dimorphic traits are limited to one sex. Such traits can arise genetically in two ways. First, the alleles that cause dimorphisms could be limited in expression to only one sex at their first appearance. Alternatively, dimorphism alleles could initially be expressed in both sexes, but subsequently be repressed or promoted in only one sex by the evolution of modifier genes or regulatory elements. We investigated these alternatives by looking for the expression of sexually dimorphic traits in female hybrids between bird species whose males show different types of ornaments. If modifier alleles or regulatory elements involved in sex-limited traits are not completely dominant, the modification should break down in female hybrids, which might then show dimorphic traits resembling those seen in males. Of 13 interspecific hybridizations examined, we found not a single instance of the expression of male-limited ornaments in female hybrids. This suggests that male ornaments were sex limited from the outset or that those traits became sex limited through the evolution of dominant modifiers -- possibly cis-dominant regulatory elements. Observing hybrid phenotypes is a useful approach to studying the genetics and evolution of dimorphic traits.
两性异形的遗传基础是进化遗传学中一个引人入胜的问题，因为二态性状仅限于一种性别。此类性状可通过两种遗传方式产生。首先，导致两性异形的等位基因在首次出现时，其表达可能仅限于一种性别。或者，二态等位基因最初可能在两性中都有表达，但随后通过修饰基因或调控元件的进化，仅在一种性别中受到抑制或促进。我们通过观察雄性具有不同类型饰羽的鸟类物种之间雌性杂种的两性异形性状表达，来研究这些可能性。如果参与性别限制性状的修饰等位基因或调控元件并非完全显性，那么这种修饰在雌性杂种中应该会失效，这样雌性杂种可能就会表现出类似于雄性的二态性状。在所研究的13次种间杂交中，我们没有发现一例雌性杂种中出现雄性限制饰羽表达的情况。这表明雄性饰羽从一开始就受到性别限制，或者这些性状通过显性修饰因子——可能是顺式显性调控元件的进化而变得受到性别限制。观察杂种表型是研究二态性状的遗传学和进化的一种有用方法。
