Mukai T, Yamaguchi O
Genetics. 1974 Feb;76(2):339-66. doi: 10.1093/genetics/76.2.339.
Six hundred and ninety-one second chromosomes were extracted from a Raleigh, North Carolina population, and the following experimental results were obtained: (1) Salivary gland chromosomes of all lines were observed and the number of inversion-carrying chromosomes was 130, among which 76 carried In(2R)NS, 36 carried In(2L)t, 4 carried In(2L)t and In(2R)NS, and 14 carried different kinds of rare inversions. (2) Viabilities of homozygotes and heterozygotes were examined. The frequency of lethal-carrying chromosomes was 275/691 (or 0.398):70/130 (or 0.538) in inversion-carrying chromosomes and 205/561 (or 0.365) in inversion-free chromosomes. The former is significantly higher than the latter. The average homozygote viability was 0.4342 including lethal lines and 0.7163 excluding those, the average heterozygote viability being 1.0000. The detrimental load to lethal load ratio (D:L ratio) was 0.334/0.501 = 0.67. The average viability of lethal heterozygotes was less than that of lethal-free heterozygotes, significantly in inversion-free individuals but not significantly so in inversion-carrying individuals. Inversion heterozygotes seem to have slightly better viability than the inversion-free heterozygotes on the average, but not significantly so. (3) The average degree of dominance of viability polygenes was estimated to be 0.293 +/- 0.071 for all heterozygotes whose component chromosomes had better viabilities than 0.6 of the average heterozygote viability, 0.177 +/- 0.077 for inversion-free heterozygotes and 0.489 +/- 0.082 for inversion heterozygotes. (4) Mutation rates of viability polygenes and lethal genes were estimated on the basis of genetic loads and average degrees of dominance of lethal genes and viability polygenes. Estimates were very close to those obtained by direct estimation. (5) Possible overdominance and epistasis were detected, but the magnitude must be very small. (6) The effective size of the population was estimated to be much greater than 10,000 by using the allelism rate of lethal-carrying chromosomes (0.0040) and their frequency.-On the basis of these findings and the comparison with the predicted result (Mukai and Maruyama 1971), the mechanisms of the maintenance of genetic variability in the population are discussed.
从北卡罗来纳州罗利市的一个种群中提取了691条第二染色体，并获得了以下实验结果：（1）观察了所有品系的唾液腺染色体，携带倒位的染色体有130条，其中76条携带In(2R)NS，36条携带In(2L)t，4条同时携带In(2L)t和In(2R)NS，14条携带不同种类的罕见倒位。（2）检测了纯合子和杂合子的活力。携带致死基因的染色体频率为275/691（或0.398）：在携带倒位的染色体中为70/130（或0.538），在无倒位的染色体中为205/561（或0.365）。前者显著高于后者。包括致死品系在内的平均纯合子活力为0.4342，不包括致死品系的平均纯合子活力为0.7163，平均杂合子活力为1.0000。有害负荷与致死负荷之比（D:L比）为0.334/0.501 = 0.67。致死杂合子的平均活力低于无致死杂合子，在无倒位个体中差异显著，在携带倒位个体中差异不显著。平均而言，倒位杂合子的活力似乎比无倒位杂合子略好，但差异不显著。（3）对于所有组成染色体活力高于平均杂合子活力0.6的杂合子，活力多基因的平均显性度估计为0.293±0.071，无倒位杂合子为0.177±0.077，倒位杂合子为0.489±0.082。（4）根据遗传负荷以及致死基因和活力多基因的平均显性度，估计了活力多基因和致死基因的突变率。估计值与直接估计得到的值非常接近。（5）检测到可能的超显性和上位性，但程度一定非常小。（6）通过使用携带致死基因的染色体的等位率（0.0040）及其频率，估计种群的有效大小远大于10000。基于这些发现并与预测结果（Mukai和Maruyama，1971）进行比较，讨论了种群中遗传变异维持的机制。
