Genetic Drift Flashcards
What is genetic drift, and how does it affect allele frequencies in populations?
Genetic drift refers to the change in allele frequencies within a population due to random sampling processes over generations. It leads to random fluctuations in allele frequencies and can result in the loss or fixation of alleles, particularly in small populations.
How does population size influence the effects of genetic drift?
In smaller populations, genetic drift has a stronger effect, causing larger shifts in allele frequencies from one generation to the next. In contrast, larger populations experience smaller changes due to better representation of sampling, which helps retain genetic variation.
What is the relationship between genetic drift and the loss of genetic variability?
Genetic drift causes a decline in genetic variability, as allele frequencies shift randomly over generations. In diploid populations, the expected heterozygosity declines by 1/(2N) each generation, where N is the population size, and this decline happens faster in smaller populations.
What is the “expected heterozygosity” (H[t]) in a population, and how is it measured?
Expected heterozygosity (H[t]) is the probability that two alleles drawn at random from a population are different alleles. It reflects the genetic diversity within the population, and declines over time due to genetic drift.
Explain the concept of “coalescence time” in population genetics.
Coalescence time refers to the time, measured in generations, since all alleles in a population can be traced back to a single common ancestor. In diploid populations, the coalescence time is approximately 4N generations, where N is the population size.
What are founder effects, and how do they impact genetic diversity?
Founder effects occur when a new population is established by a small number of individuals from a larger population. This can lead to reduced genetic diversity and increased frequency of certain alleles, including harmful ones, due to the high impact of genetic drift in small populations.
What is a genetic bottleneck, and what are its consequences for a population?
A genetic bottleneck occurs when a population undergoes a drastic reduction in size, resulting in a loss of genetic diversity. This limits the population’s ability to adapt to environmental changes and increases the risk of extinction.
How does inbreeding increase in small populations, and what is inbreeding depression?
In small populations, individuals are more likely to mate with relatives, increasing the frequency of homozygous individuals (inbreeding). Inbreeding depression refers to the negative fitness consequences of increased homozygosity, such as the rise of recessive genetic disorders.
How does genetic drift interact with selection in determining allele frequencies?
While genetic drift affects allele frequencies randomly, selection can also act on alleles, particularly in larger populations. Strong selection can overcome drift, favoring certain alleles, but in small populations, drift may overpower weak selection, even fixing slightly deleterious mutations.
What is the probability that a neutral allele will become fixed in a population due to genetic drift?
The probability that a neutral allele will become fixed due to genetic drift is equal to its initial frequency in the population (p). The smaller the frequency, the lower the chance of fixation.
Describe how drift and selection interact in diploid populations, particularly when considering the strength of selection.
In diploid populations, the fate of an allele is influenced by both selection and drift. Selection is more likely to dominate when 2hs > 1/(2N), where s is the selective advantage and N is the population size. If selection is weak or the population is small, drift may dominate, causing random fixation or loss of alleles.
What is the significance of maintaining genetic variation in a population, especially in smaller populations?
Maintaining genetic variation is crucial because it provides the raw material for evolution and adaptation to future environmental changes. In smaller populations, random events like genetic drift can reduce variation, making the population more vulnerable to extinction due to a lack of adaptability.
