Nielsen J T
Genetics. 1977 Jan;85(1):155-69. doi: 10.1093/genetics/85.1.155.
A Danish population of bank voles is polymorphic for three electrophoretically different salivary amylases; A, H and S, of which A is the most common. Both single-, double- and triple banded phenotypes were observed, and in several crosses two electrophoretic forms cosegregated. In addition to the qualitative variation, some individuals show consistent quantitative variation in the relative activities of their amylase bands. This variation has been qualified by spectrophotometrical measurements of the relative amounts of amylase protein in the various bands. --Seventy wild chromosomes were analyzed by determining the amounts of amylase they produced when heterozygous with a laboratory stock chromosome known to carry two closely linked amylase genes, both coding for a fourth electrophoretic variant, B. The amount of A-protein divided by half the amount of B-protein was used as an estimate of the number of A-genes on the tested chromosomes. The wild chromosomes fell into three clearly distinguishable classes: 9 clustered around a gene number estimate of one, 45 chromosomes yielded estimates around two genes, and the gene number estimate of the remaining 16 was close to three. The integer values of the gene number estimates and the cosegregation of electrophoretically different salivary amylases are consistent with the model that the population is polymorphic for chromosomes with either one, two, or three closely linked amylase genes. It is suggested that such gene number variation may be more common than generally recognized, and some other reported cases of quantitative enzyme variation, for instance that of human red cell acid phosphatase, are interpreted in terms of variation in the number of genes involved.
丹麦的一组林姬鼠群体中，三种经电泳区分的唾液淀粉酶（A、H和S）呈多态性，其中A最为常见。观察到了单带、双带和三带表型，并且在几次杂交中，两种电泳形式共同分离。除了定性变异外，一些个体的淀粉酶带的相对活性还表现出一致的定量变异。这种变异已通过分光光度法测量各条带中淀粉酶蛋白的相对含量得以量化。——通过测定70条野生染色体与已知携带两个紧密连锁的淀粉酶基因（均编码第四种电泳变体B）的实验室品系染色体杂合时所产生的淀粉酶量，对其进行了分析。用A蛋白的量除以B蛋白量的一半，作为对测试染色体上A基因数量的估计。野生染色体可明显分为三类：9条聚集在基因数量估计值为1的周围，45条染色体的估计值约为两个基因，其余16条的基因数量估计值接近三个。基因数量估计值的整数值以及电泳不同的唾液淀粉酶的共同分离，与该群体中具有一个、两个或三个紧密连锁的淀粉酶基因的染色体呈多态性的模型一致。有人提出，这种基因数量变异可能比普遍认为的更为常见，并且一些其他报道的定量酶变异案例，例如人类红细胞酸性磷酸酶的变异，可根据所涉及基因数量的变异来解释。
