专题：Nature报道
一种以前人们不知道的基因变异已在有关芽殖酵母（酿酒酵母的一个近亲）的一项研究中被发现。半乳糖（GAL）利用基因网络的关键特征在大多数酵母物种中都保留了下来，但芽殖酵母这个种没有功能性GAL基因，不能将半乳糖作为碳的一个来源来利用。
这项新的研究关注从日本分离得到的不能利用半乳糖的芽殖酵母与能够利用这种糖的葡萄牙分离菌种之间的差别。基因组分析显示，日本菌种中有高度退化的、非功能性GAL假基因，而葡萄牙菌种则有功能性GAL基因。
这两种不同状态（被称为“均衡的、未关联的基因网络”，简称BuGNP）似乎有一个古老起源，共存于芽殖酵母作为一个种存在的整个历史中。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 464, 54-58 (4 March 2010) | doi:10.1038/nature08791
Remarkably ancient balanced polymorphisms in a multi-locus gene network
Chris Todd Hittinger1,2, Paula Gon?alves3, José Paulo Sampaio3, Jim Dover1,2, Mark Johnston1,2 " Antonis Rokas4
1 Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, Colorado 80045, USA
2 Center for Genome Sciences, Department of Genetics, Washington University in St?Louis, School of Medicine, St?Louis, Missouri 63108, USA
3 Centro de Recursos Microbiológicos, Departamento de Ciências da Vida, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
4 Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235, USA
Local adaptations within species are often governed by several interacting genes scattered throughout the genome. Single-locus models of selection cannot explain the maintenance of such complex variation because recombination separates co-adapted alleles. Here we report a previously unrecognized type of intraspecific multi-locus genetic variation that has been maintained over a vast period. The galactose (GAL) utilization gene network of Saccharomyces kudriavzevii, a relative of brewer’s yeast, exists in two distinct states: a functional gene network in Portuguese strains and, in Japanese strains, a non-functional gene network of allelic pseudogenes. Genome sequencing of all available S. kudriavzevii strains revealed that none of the functional GAL genes were acquired from other species. Rather, these polymorphisms have been maintained for nearly the entire history of the species, despite more recent gene flow genome-wide. Experimental evidence suggests that inactivation of the GAL3 and GAL80 regulatory genes facilitated the origin and long-term maintenance of the two gene network states. This striking example of a balanced unlinked gene network polymorphism introduces a remarkable type of intraspecific variation that may be widespread.
