The Evolution of Cattle
Genetic Drift
Genetic drift describes random fluctuations of allele frequencies in a population. This can cause extreme problems in small, geographically isolated populations, where alleles become fixed or lost very easily. Genetic drift is not as common in commercial cattle operations, as genes are shared worldwide. However, small, local cattle breeds and operations need to be aware of these chance changes from generation to generation.
Mutations
Mutations are random changes in an individual's genetic makeup, which influence the gene pool. Mutations can either be harmful or advantageous, but are always a great source of genetic variation due to the introduction of new alleles. In cattle, quantitative traits (traits that are affected by many genes and environmental effects) are the source of many mutations due to so many genes being involved. One example of a beneficial mutation is the olfactory receptor genes which code for important milk traits. This mutation initially increased milk production and since then these genes have been the targets of selection in the dairy industry.
Gene Flow
Gene flow describes how genes are transferred from one population to another. Historically, gene flow through cattle migration and crossbreeding with Aurochs was very important in creating genetic variation and retaining certain traits. For example, there was gene flow between European Aurochs and British and Irish cattle breeds but not European cattle breeds. This means Aurochs did not significantly influence European cattle populations, but are significantly similar to primitive British and Irish breeds. Genetic analysis has shown that the oldest populations of cattle with the greatest geographical distance have greater diversity, while closer groups share similar genetic makeups. However, in modern breeds geographical diversification has become less pronounced due to selective breeding of high quality cattle.
Natural Selection explains the phenomenon of when populations are subject to the environment, only the fittest animals survive and pass on their genes. For cattle, this fitness could describe the ability to avoid predators, greater resistance to drought and disease, or reproductive ability. This creates phenotypic plasticity across breeds and populations that are better adapted to specific environments. With selected breeding of cattle, some favored alleles tend to decrease fitness, so natural selection works to balance this artificial selection.