Fixed allele

Definition

A fixed allele is a version of a gene that has become the only variant present in a population due to a lack of genetic diversity. When an allele reaches fixation, all individuals in the population have the same allele at that gene locus, which can significantly impact genetic variation and evolutionary processes. Fixed alleles often arise under specific conditions, such as genetic drift or strong selective pressures that favor one allele over others.

5 Must Know Facts For Your Next Test

1. Fixed alleles indicate a complete loss of variability at a specific gene locus within a population.
2. The process of fixation can occur in small populations more easily due to genetic drift, which can lead to certain alleles becoming fixed by chance.
3. When natural selection acts on a population, it can favor certain alleles over others, leading to fixation of those advantageous traits.
4. Once an allele is fixed, it may not be easily reversed unless new mutations introduce alternative alleles back into the population.
5. Fixed alleles can impact the overall adaptability of a population, as reduced genetic diversity may limit the ability to respond to environmental changes.

Review Questions

• How does genetic drift contribute to the fixation of alleles within small populations?
  • Genetic drift is a random process that can lead to fluctuations in allele frequencies, especially in small populations where chance events can have a large impact. Over time, some alleles may become more common while others may disappear entirely due to these random changes. In this way, genetic drift can result in certain alleles becoming fixed, meaning that all individuals in the population will carry the same allele at that gene locus. This loss of genetic variation can have significant consequences for the population's adaptability.
• Discuss the role of natural selection in the fixation of alleles and its implications for population evolution.
  • Natural selection plays a crucial role in determining which alleles become fixed within a population. When an allele provides a survival or reproductive advantage, individuals carrying that allele are more likely to reproduce and pass it on to future generations. Over time, this can lead to the fixation of beneficial alleles as they increase in frequency while less advantageous or neutral alleles decline. This process shapes the evolutionary trajectory of the population and impacts its ability to adapt to changing environments.
• Evaluate the significance of fixed alleles in relation to the Hardy-Weinberg Principle and what deviations from this principle imply.
  • The Hardy-Weinberg Principle establishes a baseline expectation for genetic variation in populations under ideal conditions where no evolutionary forces act. When an allele becomes fixed, it indicates a departure from this equilibrium state, highlighting that factors like natural selection or genetic drift are at play. The presence of fixed alleles signifies reduced genetic diversity and suggests that the population is undergoing evolutionary change, which could impact its long-term survival and adaptability. Understanding these deviations helps scientists assess how populations respond to environmental pressures.

Related terms

Genetic Drift: A random process that can cause changes in allele frequencies in a population, leading to the loss of genetic variation over time.

Natural Selection: The process where organisms better adapted to their environment tend to survive and produce more offspring, often resulting in the fixation of advantageous alleles.

Hardy-Weinberg Principle: A mathematical model that describes the expected genetic variation in a population under certain conditions, assuming no evolutionary forces are acting on it.