Jay L. Lush

Chance as a Cause of Changes in Gene Frequency Within Pure Breeds of Livestock

Chance deviations in gene frequency from one generation to the next, as a result of Mendelian sampling and the elimination of potential parents, are important in the pure breeds of livestock. Standard deviations of the order of .02 to .05 for gene frequencies near .5 seem to be about the usual magnitude of these chance changes in one generation. The major cause for these changes being so much larger than would be required automatically by the finite size of the population seems to be inequality in the number of gametes which the various potential parents actually contribute to the next generation. Attention to family and pedigree, plus the economic incidents which happen to whole herds, probably emphasize this more in livestock than is usual in most species in nature, although this statement about pure-bred live-stock as compared with wild species is an expression of faith which might be severely shaken if we knew more about the actual pedigrees of wild organisms!

The genetics of cattle.

Publisher Summary This chapter presents a description of the chromosome number, color inheritance, inbreeding, and other genetic characterestics of cattle. Information about the genetics of cattle has been acquired largely by studying the data that could be found concerning the resemblances between relatives. In cattle, it is sometimes possible, after a hypothesis has been devised, to make matings designed expressly to test this hypothesis and to interpret the results with no more elaborate statistical treatment than a χ 2 test. Most of the literature on cattle genetics interprets the results of matings made for some other purpose than as part of planned genetic experiments. The completeness of the findings and the validity of their interpretation are usually limited by one or more of the following circumstances: (1) the number of offspring that can be obtained from each mating is small, (2) the interval between generations is long– about five years, (3) the information on collateral relatives is often incomplete, (4) often the environmental conditions are not well controlled, either physically or statistically, (5) critical test matings are rarely conducted, although sometimes diligent search will reveal some already made, (6) only the more conspicuous characteristics and the more exceptional occurrences of the same characteristic among several close relatives are likely to be reported to the geneticist for his investigation, and (7) the number of chromosomes in cattle cells is large.