24. Factors influencing allele frequencies: mutations, migrations, natural selection.

mutation

• Mutation and Hardy-Weinberg Equilibrium: The frequencies of alleles A and a will not remain in Hardy-Weinberg equilibrium if A mutates into aa or into any other allele, and vice versa. However, mutation alone typically plays a minor role in altering allele frequencies in populations because mutation rates are generally low.

• Role of Mutation in Evolution: Despite its low rate, mutation is crucial for evolution because it is the only process that creates new alleles. These new alleles introduce genetic variation into the gene pool, providing the raw material on which natural selection and other evolutionary forces can act.

• Mutation Rate: The mutation rate is the frequency at which a specific allele changes to a different allele. It is usually expressed as the number of mutations per biological unit (e.g., per generation or per cell division). Mutation rates vary among different organisms and can differ among genes within the same organism.

migration - gene flow

• Gene Flow: Gene flow occurs when alleles are transferred between populations through the movement of individuals or their gametes (e.g., pollen). This process increases genetic diversity within a population by introducing new alleles.

• Migration and Hybridization: Gene flow can also occur through hybridization when individuals from two different populations mate, resulting in the exchange of genetic material between populations. This mixing of gene pools can significantly increase genetic variability, which can impact the population's evolutionary trajectory.

Natural Selection

• Natural Selection and Evolution: Natural selection is a mechanism that can drive evolution. It occurs when individuals with certain advantageous alleles survive and reproduce more successfully than others, leading to an increase in the frequency of those alleles in the population over time. This process is often associated with Darwinism, where "strong" or beneficial genes are more likely to persist.

• Mechanism vs. Process: It’s important to distinguish between natural selection and evolution. Natural selection is a mechanism that can lead to evolutionary change, but it is not the only one. Other mechanisms, such as genetic drift, migration, and mutation, can also cause evolution. Furthermore, natural selection will not lead to evolution unless the trait being selected is heritable.

• Adaptive Evolution: Natural selection is unique among evolutionary forces in that it can lead to adaptive evolution, where populations become better suited to their environments over time.

types of selection

• Stabilizing Selection: Favors intermediate phenotypes, reducing variation around the mean.

• Directional Selection: Favors one extreme phenotype over others, leading to a shift in the population's traits.

• Disruptive Selection: Favors extreme phenotypes at both ends of the spectrum, potentially leading to the development of two distinct forms within a population.

• Artificial Selection: This occurs when humans selectively breed organisms to enhance specific traits, such as in the breeding of domestic animals like dogs