GENETIC DRIFT AND NATURAL SELECTION Flashcards
What is genetic drift and its significance?
Genetic drift is a mechanism of evolution characterized by random changes in allele frequencies over time. It can significantly impact small populations, leading to fixation or loss of alleles and divergence between populations, which may result in speciation and loss of genetic variation.
What factors increase the impact of genetic drift?
Population Size: Smaller populations are more affected by genetic drift.
Consequences: Can lead to reduced genetic variation, making populations less adaptable to environmental changes.
What is the bottleneck effect?
The bottleneck effect occurs when a population undergoes a dramatic reduction in size due to a catastrophic event, resulting in a new population with different allele frequencies than the original population.
What is the founder effect?
The founder effect occurs when a small group splits off from a larger population to establish a new population, which may have a different genetic makeup than the original population.
What is selection and its role in evolution?
Selection occurs when heritable genetic differences lead to phenotypic differences that affect survival and reproduction. It drives evolutionary change by favoring certain traits.
What are the key assumptions of Hardy-Weinberg equilibrium?
Random mating (no assortative/disassortative mating or inbreeding)
No mutation
No selection
No genetic drift
No migration
What is non-random mating and its implications?
Non-random mating occurs when individuals do not pair randomly, affecting genotype frequencies.
Assortative Mating: Leads to more homozygous individuals than expected.
Disassortative Mating: Leads to more heterozygous individuals than expected.
Inbreeding: Similar to assortative mating, it increases homozygosity.
What is stabilizing selection?
Stabilizing selection favors the average phenotype and selects against extremes, reducing variation in a trait and maintaining uniform populations.
What is directional selection?
Directional selection favors one extreme phenotype over others, causing a shift in the population’s trait distribution and changing the mean value of a trait.
What is disruptive selection?
Disruptive selection favors both extremes of a trait and selects against the average phenotype, potentially increasing genetic diversity and leading to the formation of new species.
How is relative fitness calculated?
Relative fitness (W) is calculated as the number of offspring of a genotype divided by the number of offspring of the most fit genotype.
What is the selection coefficient?
The selection coefficient (S) measures the reduction in fitness of a genotype compared to the most fit genotype, calculated as
S=1−W.
Ranges from 0 (no selection) to 1 (maximum selection against the genotype).
What is inbreeding depression?
Inbreeding depression is the reduction in fitness and health of a population due to increased homozygosity, raising the chance of inheriting harmful recessive alleles and resulting in higher occurrences of genetic disorders.
How does selection impact allele frequencies?
Selection can lead to fixation or loss of alleles, divergence between populations, or increased similarity within a population, thereby influencing genetic variation.
What role do mutations play in genetic variation?
Mutations introduce new alleles to a population, starting at frequencies proportional to population size.
Haploid Population: After mutation, frequency is
1/N.
Diploid Population: After mutation, frequency is
1/(2N).
