Deleterious Recessive Genes in Dairy Bulls Selected at Random.

HE genetics of farm mammals have not been investigated in a manner T comparable to the intensive studies made, during the last forty years, with Drosophila, laboratory rodents, and chickens. Nevertheless, a large number of mutant genes have been reported in farm mammals. These mutants have been discovered more or less by chance when sufficient inbreeding has brought them to light. Many more have probably occurred that were not reported. Several investigators-Hum (1934), EATON (1937), MOHR (1939), and others-have compiled these mutants from time to time. LERNER (1944) has made the most recent compilation. His check lists for cattle, horses, swine, sheep, and chickens show that cattle lead, with 2 5 lethals. Since, however, there are two recognizable phenotypes of recessive achondroplasia, the number is 26. The undesirable nonlethals reported are probably more numerous, but there is no compilation of them. This paper will summarize the occurrence of the undesirable recessive genes that were found in the original sires tested in the California dairy cattle breeding experiment. It is realized that the data are insufficient to establish gene frequency values, mutation rates, and other related values pertinent to the dairy cattle population as a whole. Perhaps this report will stimulate other investigators with similar data to publish, so that eventually sufficient data will be amassed to permit a complete study of gene frequencies and related phenomena in cattle.