木曾馬集団における毛色の頻度の推移

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The so-called Kiso native horses, bred in Nishi-Chikuma Country of Nagano Prefecture in Japan, were investigated for frequencies of appearance of various coat colors from their breeding records and by direct observation.In the population of these horses, the frequency of appearance of a bay color has been increasing from year to year, that of a black color decreasing, and that of a chestnut color (and a liver-chestnut color) retained about a constant value. The sum of frequencies of appearance of buckskin and of palomino was only 5% or less. These changes in frequency could be translated into those in gene frequency. The frequency of gene a (qa), which was about 0.55 in 1943, decreased gradually and reached about 0.35 in 1960. The frequency of gene b (qb) retained nearly a constant value (0.45). The frequency of gene D (qD) was about 0.02. These phenomena suggest that two types of polymorphism, transient and balanced, controlled the change in frequency of appearance of a coat color.The analysis on the genetical mechanism of polymorphism revealed that there were two factors of selection. One was the selection which acted when a sire and a dam were chosen and, the other the selection which was supported to act upon the developing fetus. The two factors of selection acted additionally to decrease the frequency of gene a. On the other hand, the effects of these factors on gene b were antagonistic against each other; that is, the former factor acted to decrease and the later to increase the frequency of this gene.
社団法人日本畜産学会の論文

木曾馬集団における毛色の頻度の推移

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