Cell Biology
In the simplest sense, evolution is a change in the gene pool of a population over time. Scientists measure changes in a population's gene pool by comparing allele frequencies, which are measures of how prevalent each allele is. Alleles are different versions of the same gene that impact how the gene functions. Evolution occurs when the frequency of an allele changes over time, and by the scientific definition, only populations can evolve, not individuals.
For evolution to occur, a population must experience at least one evolutionary process. There are five of these processes: genetic drift, mutation, gene flow, natural selection, and non-random mating, which includes artificial and sexual selection. Each of the five evolutionary processes contributes to the change in allele frequencies in a population, leading to evolution over time.
Lesson Outline
<ul> <li>Defining and measuring evolution <ul> <li>Evolution is a change in the gene pool of a population over time</li> <li>Scientists compare allele frequencies to measure changes in a population's gene pool</li> <li>Alleles are different versions of the same gene and are typically represented in population genetics by the letters "p" and "q"</li> </ul> </li> <li>Conditions for Evolution <ul> <li>Only populations can evolve, not individuals</li> <li>A population must experience at least one evolutionary process</li> </ul> </li> <li>Evolutionary processes <ul> <li>Genetic drift</li> <li>Mutation</li> <li>Gene flow</li> <li>Natural selection</li> <li>Non-random mating (artificial and sexual selection)</li> </ul> </li> </ul>
Don't stop here!
Get access to 35 more Cell Biology lessons & 8 more full MCAT courses with one subscription!
FAQs
Evolution is the process of change in the inherited characteristics of species over successive generations, driven by mechanisms such as natural selection, mutation, gene flow, and genetic drift. It is closely related to allele frequencies and the gene pool, as evolution occurs when there are changes in the relative frequency of alleles (different forms of a gene, typically represented by the letters "p" and "q") within a population's gene pool. As these frequencies change over time, populations can become more or less adapted to their environment, which can ultimately lead to the development of new species.
Natural selection is a key mechanism of evolution, which acts on the variation within a population by favoring individuals that possess traits advantageous to surviving and reproducing in their environment. As a result, such beneficial traits become more prevalent in the population over time, as those organisms with these traits are more likely to pass them on to the next generation. This process allows populations to adapt to their environment, as individuals with more favorable traits outcompete those with less advantageous traits.
Genetic drift is a random process by which allele frequencies in a population change over time, independent of selective pressures. Genetic drift occurs mainly due to chance events, such as the random sampling of gametes during reproduction or the random death of individuals. In small populations, genetic drift can have a significant impact on allele frequencies, which may cause genetic variation to become lost or fixed over time. These changes can ultimately contribute to evolutionary processes and the formation of new species, especially when combined with other evolutionary forces such as natural selection or gene flow.
Gene flow is the exchange of genetic material between populations, either through migration or the transfer of gametes, which can have a direct effect on the evolution of a population by introducing new genetic variation or altering existing allele frequencies. Gene flow can increase genetic diversity within populations, potentially increasing their ability to adapt to their environment. Conversely, it may also hinder local adaptation if new alleles disrupt favorable combinations of traits. Non-random mating is the selection of mates based on certain traits or characteristics, leading to deviations from random mating expectations and altering the frequencies of genotypes in the population. This can profoundly impact the distribution of traits within populations, as individuals with certain characteristics are more likely to reproduce. Non-random mating can be a form of sexual selection or may be the result of other mate choice mechanisms (such as artificial selection), and it can contribute to the evolution of new traits or species.
Artificial selection and sexual selection are both types of non-random mating, but they involve different processes by which traits become favored in a population. Artificial selection is a process in which humans intentionally select and breed individuals with specific traits, leading to changes in the frequency of those traits within the population. This process can result in rapid changes in trait distribution and has been widely used in agriculture and animal breeding. Sexual selection, on the other hand, is a form of natural selection in which individuals with certain traits have greater reproductive success due to a competitive advantage in mating. This can result from traits that increase an individual's chances of attracting a mate (e.g., bright plumage in birds) or increase the likelihood of successfully competing with others for a mate (e.g., antler size in deer). Over time, sexual selection can lead to the development of exaggerated or seemingly maladaptive traits, as these traits are favored due to their role in reproductive success.
