10.3.2:

 Evolution requires that allele frequencies change with time in populations

Changes within a gene pool occurring from generation to generation is known as microevolution. Allele frequencies in a population may change due to gene flow, genetic drift, natural selection and mutation. These are referred to as the four fundamental forces of evolution. Only mutation can create new genetic variation. the other three forces simply rearrange this variation within and among populations.

Gene pools are usually stable over time, however as a result of a mutation new alleles can be introduced, and old alleles can disappear when the last organism carrying the allele dies. A result of evolution is that after many generations of natural selection, some alleles prove to be advantageous and tend to be more frequent.

Particular alleles can limit the survival of the organisms in the population, and are not passed on to as many offspring. An allele frequency can be estimated at any time, however it is only a snapshot of the alleles at that particular time. In future generations, the proportions of the alleles would have changed.

If specific populations mix because of immigrations, a change in allele frequencies will occur. This remains the same for emigrations, when one group with a particular allele leaves the population it will change. If a gene pool is modified and the allele frequencies change, some degree of evolution has happened. No change in allele frequencies, however, means no evolution.

In order to calculate the frequencies of alleles, genotypes and phenotypes within a population, the Hardy- Weinberg equation is used.  This equation is useful to determine how fast a population is changing, or predicting the outcomes of matings.