Department of Biology, Kyushu University, Fukuoka 812, Japan.
Genetics. 1983 Sep;105(1):115-34. doi: 10.1093/genetics/105.1.115.
About 500 second and 500 third chromosomes were extracted, using the marked inversion technique, from the Orlando-Lake Placid, Florida, population. From the experiments using these chromosomes, the following findings were obtained: (1) The frequencies of lethal-carrying chromosomes were 0.37 in the second and 0.55 in the third chromosomes. (2) The size of the population was estimated to be effectively infinite, on the basis of the allelism rate of lethal-carrying chromosomes. (3) The detrimental and lethal loads for viability were, respectively, 0.40 and 0.45 for the second and 0.52 and 0.78 for the third chromosomes. Consequently, the detrimental to lethal load ratio is 0.90 for the second and 0.67 for the third chromosomes. (4) Lethal genes were shown to be deleterious when heterozygous. (5) The average degree of dominance for mildly deleterious genes (viability polygenes) was estimated to be nearly 0.5, although the confidence interval is large. (6) Additive (sigma( 2) (A)) and dominance (sigma(2) ( D)) variances of viability were estimated by using a partial diallel cross method. The results were (see PDF) and (see PDF) for the second chromosomes. (7) Environmental variances of viability were estimated. The result indicates that the heterozygotes are more homeostatic than the homozygotes. The most striking finding is that the additive variance is larger than expected on the classical hypothesis from the detrimental load. Several possible explanations for the discrepancy are offered. The most likely cause, we suggest, is genotype-environment interaction (diversifying selection) acting on viability polygenes. Overdominance is inconsistent with the low dominance variance, and frequency-dependent selection also appears unlikely as an explanation.
约 500 条第二号染色体和 500 条第三号染色体，是用标记倒位技术从佛罗里达州奥兰多-莱克普雷里迪（Orlando-Lake Placid）种群中提取出来的。通过对这些染色体的实验，得到了以下结果：（1）第二号染色体携带致死基因的频率为 0.37，第三号染色体为 0.55。（2）根据携带致死基因染色体的等位基因频率，估计种群规模实际上是无限的。（3）第二号和第三号染色体对生存力的有害和致死负荷分别为 0.40 和 0.45，0.52 和 0.78。因此，第二号染色体的有害与致死负荷比为 0.90，第三号染色体为 0.67。（4）当杂合时，致死基因被证明是有害的。（5）对于轻度有害基因（生存力多基因）的平均显性程度估计接近 0.5，尽管置信区间较大。（6）使用部分双列杂交法估计了生存力的加性（σ 2 (A)）和显性（σ 2 (D)）方差。结果分别为第二号染色体的（见 PDF）和（见 PDF）。（7）估计了生存力的环境方差。结果表明，杂合子比纯合子更具有同型性。最引人注目的发现是，加性方差大于根据有害负荷的经典假设所预期的大小。我们提出了几种可能的解释来解释这种差异。最有可能的原因是，生存力多基因的基因型-环境相互作用（多样化选择）在起作用。超显性与低显性方差不一致，频率依赖性选择似乎也不太可能作为一种解释。
