Microevolution

          Microevolution is a change in gene frequency within a population. This change is due to four different processes mutation selection , gene flow and genetic drift
population genetics is the branch of biology that provides the mathematical structure for the study of the process of microevolution. Ecological genetics concerns itself with observing microevolution in the wild. Typically, observable instances of evolution are examples of microevolution; for example, bacterial strains that have antibiotic resistance
Microevolution can be contrasted with  marcoevolution, which is the occurrence of large-scale changes in gene frequencies in a population over a geological time period  difference is largely one of approach. Microevolution is reductionist, but macroevolution is . Each approach offers different insights into the evolution process. Macroevolution can be seen as the sum of long periods of microevolution, and thus the two are qualitatively identical while being quantitatively different.