Shimada T, Hasegawa T, Matsumoto K, Agui N, Kobayashi M
Department of Agrobiology, University of Tokyo, Japan.
Genet Res. 1994 Jun;63(3):189-95. doi: 10.1017/s0016672300032341.
We looked for polymorphism of the prothoracicotropic hormone gene locus (Ptth) among inbred strains of the silkmoth, Bombyx mori, by in vitro DNA amplification (polymerase chain reaction), and found three alleles, PtthA, PtthB and PtthC. The PtthA allele contained a third intron consisting of 680 bp and a fourth intron of 350 bp. PtthB contained the same size third intron but a longer fourth intron of 490 bp, while PtthC had a longer third intron of 1080 bp and a shorter fourth intron of 350 bp. In 29 strains which we examined, 9 strains had PtthA, 8 strains had PtthB, and 2 strains had PtthC. The other 10 strains had heterogeneous genotypes with the same 3 alleles. Linkage analyses using these polymorphisms showed that Ptth was linked to the or gene on chromosome 22, and was independent of other chromosome markers. To determine the map position, we obtained an F1 hybrid between the w41 strain (PtthC+or+mw) and the w22 strain (PtthB or mw), and backcrossed the F1 hybrid to females of the w22 strain. From the segregation of or, mw and Ptth in 861 progeny, recombination values were calculated as 18.5% between or and mw, 23.9% between mw and Ptth, and 7.3% between Ptth and or. Because or and mw have already been mapped at positions 22-8.9 cM and 22-25.2 cM, respectively, we mapped Ptth at 22-2.5 cM. The Ptth locus is independent of any loci which are known to control growth and molting.
我们通过体外DNA扩增（聚合酶链反应），在家蚕近交系中寻找促前胸腺激素基因位点（Ptth）的多态性，发现了三个等位基因，即PtthA、PtthB和PtthC。PtthA等位基因包含一个由680 bp组成的第三内含子和一个350 bp的第四内含子。PtthB包含相同大小的第三内含子，但第四内含子更长，为490 bp，而PtthC的第三内含子更长，为1080 bp，第四内含子更短，为350 bp。在我们检测的29个品系中，9个品系有PtthA，8个品系有PtthB，2个品系有PtthC。其他10个品系具有包含相同3个等位基因的异质基因型。利用这些多态性进行的连锁分析表明，Ptth与22号染色体上的or基因连锁，并且与其他染色体标记独立。为了确定图谱位置，我们获得了w41品系（PtthC+or+mw）和w22品系（PtthB or mw）之间的F1杂种，并将F1杂种与w22品系的雌蛾回交。根据861个后代中or、mw和Ptth的分离情况，计算出or与mw之间的重组值为18.5%，mw与Ptth之间为23.9%，Ptth与or之间为7.3%。由于or和mw已经分别定位在22-8.9 cM和22-25.2 cM的位置，我们将Ptth定位在22-2.5 cM处。Ptth位点与任何已知控制生长和蜕皮的位点无关。
