Simmons M J, Raymond J D, Culbert T P, Laverty T R
Genetics. 1984 May;107(1):49-63. doi: 10.1093/genetics/107.1.49.
The Q strain known as v6 was tested for its ability to induce X-linked lethal mutations in male and female hybrids from crosses with M strains in the P-M system of hybrid dysgenesis. All measurements of the mutation rate were made on the X chromosome derived from the v6 strain. The lethal rate for young hybrid males from the cross M female X v6 male was 1.11% per chromosome. For older males, it was only 0.44%, suggesting that there is less mutational or more repair activity in the germ cells of the older males or that mutant cells are selectively eliminated as the hybrid males age. The lethal rate for hybrid females from comparable crosses was approximately the same for both ages that were tested. However, it was substantially less than the rate for the hybrid males--only 0.26% per chromosome. Genetically identical hybrid females from reciprocal crosses also showed a low mutation rate, 0.13% per chromosome. Again, there was no difference between young and old flies. Mapping experiments established that most of the lethal mutations that were recovered from the male and female hybrids were located in two regions on the X chromosome, one between bands 14B13 and 15A9 , the other between bands 19A1 and 20A , which encompasses the maroonlike locus. More refined mapping of the lethals in the maroonlike region demonstrated that the vast majority of these affected a single gene located in band 19C4 . Cytological analysis of the lethal chromosomes revealed that several carried rearrangements, including inversions, duplications and deficiencies. Chromosome breakage occurred primarily in bands 14D1 -3 and 18F- 20A , and most of the breaks in the latter segment were located in 19C . However, rearrangements involving 19C and mutations of the gene in 19C4 were mutually exclusive events. In situ hybridization of a P element probe to the chromosomes of v6 demonstrated that P elements reside at a minimum of five sites on the X chromosome. These P element sites correspond to the mutational and breakage hot spots on that chromosome. The combined genetic and cytological data imply that most of the X-linked lethal mutations that occur in M X v6 hybrids are due to local P element action. Consideration of these and other data suggest that v6 is a weak P strain in the P-M system of hybrid dysgenesis and that other Q strains might also be regarded in this way.
在杂种不育的P-M系统中，对名为v6的Q品系进行了测试，以考察其在与M品系杂交产生的雄性和雌性杂种中诱导X连锁致死突变的能力。所有突变率的测量均基于来自v6品系的X染色体。M雌蝇与v6雄蝇杂交产生的年轻杂种雄蝇的致死率为每条染色体1.11%。对于年龄较大的雄蝇，该致死率仅为0.44%，这表明年龄较大的雄蝇生殖细胞中的突变活性较低或修复活性较高，或者随着杂种雄蝇年龄增长，突变细胞被选择性清除。在两个测试年龄中，类似杂交产生的杂种雌蝇的致死率大致相同。然而，该致死率显著低于杂种雄蝇的致死率——仅为每条染色体0.26%。正反交产生的基因相同的杂种雌蝇也显示出较低的突变率，为每条染色体0.13%。同样，年轻和年老的果蝇之间没有差异。定位实验表明，从雄性和雌性杂种中获得的大多数致死突变位于X染色体的两个区域，一个在14B13和15A9带之间，另一个在19A1和20A带之间，后者包含类褐眼基因座。对类褐眼区域致死突变的更精细定位表明，这些突变绝大多数影响位于19C4带的单个基因。对致死染色体的细胞学分析表明，其中几条染色体发生了重排，包括倒位、重复和缺失。染色体断裂主要发生在14D1 - 3带和18F - 20A带，后一区域的大多数断裂位于19C带。然而，涉及19C带重排和19C4带基因的突变是相互排斥的事件。用P因子探针与v6染色体进行原位杂交表明，P因子至少存在于X染色体的五个位点。这些P因子位点与该染色体上的突变和断裂热点相对应。综合的遗传学和细胞学数据表明，M×v6杂种中发生的大多数X连锁致死突变是由局部P因子作用引起的。对这些数据和其他数据的思考表明，v6是杂种不育P-M系统中的一个弱P品系，其他Q品系可能也应如此看待。
