The present studies were carried out to analyze according to the allocation method the phenogroups of the D system in the light breed horses ( Thoroughbreds and Anglo-Arabs ) of Japan. The results are as follows:
1. The D system in the light breed horses consisted of six alleles of
Dbc, Dcg, Dg, Dfl, Dl and
D-, and their gene frequencies were 0.169, 0.429, 0.020, 0.030, 0.350 and 0.002, respectively.
2. As the result of studies on the D system of about 35, 000 horses, the
D-/D-type was not observed at all. And also, taking thought for the segregation data of the Dl factor in the offsprings obtained from matings between the D
l factor positive and negative individuals, it could be surmised that the D system is closed through the D
l factor. However, a few exceptions to that rule were encountered.
3. To analyze the phenogroups was not difficult because the D system consisted of simple phenogroups.
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