McColl G, Hoffmann A A, McKechnie S W
Department of Genetics and Developmental Biology, Monash University, Clayton, Australia.
Genetics. 1996 Aug;143(4):1615-27. doi: 10.1093/genetics/143.4.1615.
To identify genes involved in stress resistance and heat hardening, replicate lines of Drosophila melanogaster were selected for increased resistance to knockdown by a 39 degrees heat stress. Two selective regimes were used, one with and one without prior hardening. Mean knockdown times were increased from approximately 5 min to > 20 min after 18 generations. Initial realized heritabilities were as high as 10% for lines selected without hardening, and crosses between lines indicated simple additive gene effects for the selected phenotypes. To survey allelic variation and correlated selection responses in two candidate stress genes, hsr-omega and hsp68, we applied denaturing gradient gel electrophoresis to amplified DNA sequences from small regions of these genes. After eight generations of selection, allele frequencies at both loci showed correlated responses for selection following hardening, but not without hardening. The hardening process itself was associated with a hsp68 frequency change in the opposite direction to that associated with selection that followed hardening. These stress loci are closely linked on chromosome III, and the hardening selection established a disequilibrium, suggesting an epistatic effect on resistance. The data indicate that molecular variation in both hsr-omega and.hsp68 contribute to natural heritable variation for hardened heat resistance.
为了鉴定参与抗逆性和热驯化的基因，选用黑腹果蝇的重复品系，通过39摄氏度热应激来提高对击倒的抗性。使用了两种选择方案，一种有预先驯化，一种没有。经过18代后，平均击倒时间从大约5分钟增加到了20分钟以上。对于未经过驯化选择的品系，初始实现遗传力高达10%，品系间杂交表明所选表型存在简单的加性基因效应。为了研究两个候选应激基因hsr-omega和hsp68中的等位基因变异及相关选择反应，我们对这些基因小区域的扩增DNA序列应用了变性梯度凝胶电泳。经过八代选择后，两个位点的等位基因频率在驯化后显示出相关的选择反应，但未驯化时则没有。驯化过程本身与hsp68频率的变化方向相反，而hsp68频率变化方向与驯化后的选择相关。这些应激位点在第三条染色体上紧密连锁，驯化选择建立了一种不平衡状态，表明对抗性存在上位效应。数据表明，hsr-omega和hsp68的分子变异都对驯化后的耐热性自然遗传变异有贡献。
