(Remember that we studied genotypes and allele frequencies when we explored inheritance patterns proposed by Mendel.) For example, scientists examining allele frequencies in a pesticide resistance gene in mosquitoes at Equatorial Guinea found that the frequency of one resistance allele was 6.3%, while a second resistance allele’s frequency was 74.6%, and the non-resistance allele’s frequency was 19.0%.

Population genetics studies microevolution by measuring changes in a population’s allele frequencies over time.

The theory also connects this change of a population over time, called microevolution, with the processes that gave rise to new species and higher taxonomic groups with widely divergent characters, called macroevolution. In sum, the modern synthesis describes how evolutionary processes, such as natural selection, can affect a population’s genetic makeup, and, in turn, how this can result in the gradual evolution of populations and species. But over the next few decades genetics and evolution were integrated in what became known as the modern synthesis-the coherent understanding of the relationship between natural selection and genetics that took shape by the 1940s and is generally accepted today. Initially, the newly discovered particulate nature of genes made it difficult for biologists to understand how gradual evolution could occur. Mendel’s work was rediscovered in the early twentieth century at which time geneticists were rapidly coming to an understanding of the basics of inheritance. Darwin and Wallace were unaware of the genetics work by Austrian monk Gregor Mendel, which was published in 1866, not long after publication of Darwin's book, On the Origin of Species. In fact, the predominant (and incorrect) genetic theory of the time, blending inheritance, made it difficult to understand how natural selection might operate. This lack of understanding was a stumbling block to understanding many aspects of evolution. The mechanisms of inheritance, or genetics, were not understood at the time Charles Darwin and Alfred Russel Wallace were developing their idea of natural selection. What is the Hardy–Weinberg principle, and how can it be applied to microevolution?.What is population genetics and how is population genetics a synthesis of Mendelian inheritance and Darwinian evolution?.In this section, you will explore the following questions:

Gene flow ap bio