Sawamura Kyoichi, Tomimura Yoshihiko, Sato Hajime, Yamada Hirokazu, Matsuda Muneo, Oguma Yuzuru
Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
Genet Res. 2006 Aug;88(1):1-11. doi: 10.1017/S0016672306008299.
Strong sexual isolation exists between the closely related species Drosophila ananassae and D. pallidosa, but there is no obvious post-mating isolation; both sexes of the hybrids and their descendants appear to be completely viable and fertile. Strains exhibiting parthenogenesis have been derived from wild populations of both species. We intercrossed such strains and established iso-female lines after the second generation of parthenogenesis. These lines are clones, carrying homozygous chromosomes that are interspecific recombinants. We established 266 such isogenic lines and determined their genetic constitution by using chromosomal and molecular markers. Strong pseudo-linkage was seen between loci on the left arm of chromosome 2 and on the right arm of chromosome 3; the frequency of inheriting the two chromosome regions from the same species was significantly larger than expected. One possible cause of pseudo-linkage is female meiotic bias, so that chromosomes of the same species origin tend to be distributed to the same gamete. But this possibility is ruled out; backcross analysis indicated that the two chromosome regions segregated independently in female hybrids. The remaining possibility is elimination of low-fitness flies carrying the two chromosome regions from different species. Thus, genetic incompatibility was detected in the species pair for which no hybrid breakdown had previously been indicated. The 'interspecific mosaic genome' lines reported here will be useful for future research to identify genes involved in speciation and phenotypic evolution.
在亲缘关系密切的物种果蝇（Drosophila ananassae）和苍白果蝇（D. pallidosa）之间存在强烈的性隔离，但不存在明显的交配后隔离；杂种及其后代的雌雄个体似乎都完全存活且可育。已从这两个物种的野生种群中获得了表现出孤雌生殖的品系。我们将这些品系进行杂交，并在第二代孤雌生殖后建立了同雌系。这些品系是克隆体，携带的纯合染色体是种间重组体。我们建立了266个这样的同基因系，并使用染色体和分子标记确定了它们的遗传组成。在2号染色体左臂和3号染色体右臂上的基因座之间观察到强烈的假连锁；从同一物种继承这两个染色体区域的频率明显高于预期。假连锁的一个可能原因是雌性减数分裂偏向，即同一物种来源的染色体倾向于分布到同一个配子中。但这种可能性被排除了；回交分析表明，这两个染色体区域在雌性杂种中独立分离。剩下的可能性是淘汰携带来自不同物种的这两个染色体区域的低适应性果蝇。因此，在之前未显示杂种衰退的物种对中检测到了遗传不相容性。本文报道的“种间镶嵌基因组”品系将有助于未来研究鉴定参与物种形成和表型进化的基因。
