[Problems in the genetics of bovine leukemia. II. The effect of fathers and mothers on the leukemia disease frequency in the progeny].

Geneology of 14,000 animals which are the progeny of 554 bulls are studied, 2060 of them having leucosis. Differences between bulls in the frequency of the disease in daughters are observed. The morbidity of daughters of bulls having leucosis is higher than for the population in the average. The morbidity of the animals depends on the linear relation animals. "Leucosis" families having a high concentration of ill animals for several generations, and families resistant to leucosis are revealed. Daughters of leucosis mothers got ill more often than those of healthy animals. The coefficient of heritability of leucosis ranges from 0.07 to 0.50. Concordancy for leucosis in unisexual twins is 74.1%. Insignificant increase in leucosis is found for the last three generations. Predisposition for leucosis is characterized by a complex hereditary condition. The portion of genetic factors is quite enought to conduct the animal selection for leucosis resistance.