Concept 23.3: Natural selection, genetic drift, and gene flow can alter allele frequencies in a population

Flashcards from Concept 23.3 of Pearson's Campbell Biology, Twelfth Edition.

Hardy-Weinberg equilibrium

State at which a population is not evolving, given the required conditions of no mutations, random mating, no natural selection, large population size, and no gene flow

Most affected by:

• Natural selection

• Genetic drift

• Gene flow

Natural selection

Process in nature based on differential success in survival and reproduction

• Traits better suited to the environment produce more offspring than others, resulting in different proportions

Adaptive evolution

A process in which traits that enhance survival or reproduction increase in frequency over time as a result of natural selection

Genetic drift

A process in which chance events cause allele frequencies to fluctuate unpredictably from one generation to the next

• Tends to reduce genetic variation through the random loss of alleles

• More significant in small populations; can lead to the fixation of harmful alleles

Founder effect

Occurring when a few individuals become isolated from a larger population, allele frequencies in the smaller population are different from those in the parent population

Bottleneck effect

Occurring when there is a drastic reduction in population size due to a sudden change in the environment, the resulting gene pool may no longer be reflective of the original population’s gene pool

• Seen with the severe reduction of prairie chicken habitats in Illinois leading to low genetic variation and an increase in the frequency of harmful alleles; solved through the introduction of birds from other populations leading to better egg-hatching rates

Gene flow

The movement of alleles among populations, transferred through the movement of fertile individuals or gametes

• Tends to reduce variation among populations over time

• Can affect adaptation to local environments or different threats in varying ways due to these new traits