Fixation of alleles

Definition

Fixation of alleles refers to the process by which a specific allele becomes the only variant present at a particular gene locus in a population. This occurs when the frequency of that allele reaches 100%, meaning all individuals in the population carry the same allele, leading to a loss of genetic diversity. This concept is closely linked to genetic drift, particularly in small populations where chance events can drastically change allele frequencies.

5 Must Know Facts For Your Next Test

1. Fixation can occur quickly in small populations due to genetic drift, where random events can lead to the dominance of one allele.
2. Once an allele is fixed, it eliminates other alleles at that locus, which can reduce the overall genetic diversity and adaptability of the population.
3. In contrast to natural selection, fixation is often a result of random processes rather than adaptive advantages.
4. In large populations, fixation is less common because the larger number of individuals can maintain multiple alleles through balancing selection or gene flow.
5. The founder effect often leads to fixation because the new population starts with a limited genetic pool, increasing the likelihood that some alleles will become fixed.

Review Questions

• How does genetic drift contribute to the fixation of alleles within small populations?
  • Genetic drift leads to random fluctuations in allele frequencies, especially in small populations where chance events can have a large impact. Over generations, certain alleles may become more common purely by chance, eventually reaching fixation where only one allele remains at a particular locus. This random process can result in significant changes in genetic composition without any selection pressure involved.
• Discuss the implications of the founder effect on genetic diversity and allele fixation in newly established populations.
  • The founder effect occurs when a small group breaks away from a larger population to establish a new one. This small founding group typically has limited genetic diversity, which can lead to certain alleles becoming fixed as they reproduce in isolation. The resulting population may exhibit reduced genetic variation compared to the original population, impacting its adaptability and potentially increasing its vulnerability to environmental changes or diseases.
• Evaluate how the fixation of alleles affects evolutionary dynamics and species adaptation over time.
  • The fixation of alleles can significantly shape evolutionary dynamics by reducing genetic diversity within populations. When an allele becomes fixed, it limits the range of potential adaptive traits that could respond to environmental changes. This lack of variability can hinder a species' ability to adapt over time, making them more susceptible to extinction under shifting conditions. In some cases, however, if the fixed allele provides a strong adaptive advantage, it may enhance survival and reproductive success, demonstrating how fixation can be both detrimental and beneficial depending on context.

Related terms

genetic drift: A mechanism of evolution that refers to random changes in allele frequencies in a population, which can lead to the fixation or loss of alleles over time.

founder effect: A type of genetic drift that occurs when a small group from a larger population establishes a new population, potentially carrying only a small fraction of the genetic diversity from the original group.

allele frequency: The proportion of a specific allele among all allele copies in a population, used to measure genetic variation.