All flashcards
Flashcard 1: What is the founder effect?
Answer: Drift from a new population started by a small number of individuals. The founder effect arises when a small group colonizes a new area, carrying only a subset of alleles that then drift in the isolated population.
Flashcard 2: Find the heterozygote frequency if p=0.6 and q=0.4 under Hardy–Weinberg.
Answer: 2pq=0.48. Heterozygote frequency is twice the product of allele frequencies, derived from Hardy–Weinberg principles for random mating.
Flashcard 3: What is fitness in evolutionary biology (as used in natural selection questions)?
Answer: Relative reproductive success of a genotype or phenotype. Fitness measures an organism's ability to pass on genes relative to others, driving natural selection by favoring advantageous genotypes or phenotypes.
Flashcard 4: What is the ultimate source of new alleles in a population?
Answer: Mutation. Mutations introduce novel genetic variation by altering DNA sequences, providing raw material for evolution unlike other mechanisms that redistribute existing alleles.
Flashcard 5: What is genetic drift?
Answer: Random change in allele frequencies due to chance sampling. Genetic drift causes unpredictable fluctuations in allele frequencies from random sampling errors, especially pronounced in small populations.
Flashcard 6: Which mechanism is more influential in small populations: genetic drift or selection?
Answer: Genetic drift. In small populations, random sampling errors dominate over selective pressures, making genetic drift the primary driver of allele frequency changes.
Flashcard 7: What is the bottleneck effect?
Answer: Drift after a drastic population size reduction. Bottlenecks reduce genetic diversity through drastic population declines, amplifying drift as surviving alleles are randomly sampled from the remnant group.
Flashcard 8: What is gene flow (migration) and its typical effect on population differences?
Answer: Allele movement between populations; reduces population divergence. Gene flow homogenizes allele frequencies across populations by introducing alleles via migration, counteracting differentiation caused by drift or local selection.
Flashcard 9: What is stabilizing selection?
Answer: Selection favoring intermediate phenotypes; reduces variance. Stabilizing selection maintains phenotypic optima by eliminating extremes, preserving the population mean while narrowing trait distribution.
Flashcard 10: What is directional selection?
Answer: Selection favoring one extreme phenotype; shifts the mean. Directional selection drives evolutionary change by increasing the frequency of advantageous extreme traits, shifting the population's phenotypic mean accordingly.
Flashcard 11: What is disruptive selection?
Answer: Selection favoring both extremes; can increase variance/bimodality. Disruptive selection promotes polymorphism by favoring phenotypic extremes over intermediates, potentially leading to speciation through increased variance.
Flashcard 12: What is sexual selection?
Answer: Selection on traits that increase mating success. Sexual selection evolves traits that enhance mating opportunities, often through competition or choice, even if they reduce overall survival fitness.
Flashcard 13: What is heterozygote advantage (overdominance)?
Answer: Heterozygote has higher fitness than either homozygote. Heterozygote advantage maintains genetic diversity by conferring superior fitness to carriers of both alleles, as seen in sickle-cell anemia resistance to malaria.
Flashcard 14: What is the definition of evolution in a population genetics context?
Answer: Change in allele frequencies in a population over generations. Evolution is defined as shifts in allele frequencies across generations due to mechanisms like selection, drift, mutation, and gene flow acting on genetic variation.
Flashcard 15: What is natural selection, stated in terms of fitness and heritable variation?
Answer: Differential reproductive success due to heritable trait differences. Natural selection occurs when heritable traits confer varying reproductive success, leading to changes in trait frequencies over generations.
Flashcard 16: What is frequency-dependent selection?
Answer: Fitness of a phenotype depends on its frequency in the population. Frequency-dependent selection stabilizes polymorphisms as rare phenotypes gain advantages, preventing fixation and promoting coexistence of multiple strategies.
Flashcard 17: What is the definition of Hardy–Weinberg equilibrium?
Answer: Allele and genotype frequencies remain constant absent evolutionary forces. Hardy–Weinberg equilibrium assumes no evolutionary forces, allowing prediction of stable frequencies from random mating in idealized populations.
Flashcard 18: Which five conditions must hold for Hardy–Weinberg equilibrium to apply?
Answer: No selection, no mutation, no migration, random mating, large population. These conditions ensure no changes in allele frequencies, enabling mathematical modeling of genotype proportions under equilibrium.
Flashcard 19: State the Hardy–Weinberg allele frequency equation using p and q.
Answer: p+q=1. For a locus with two alleles, their frequencies sum to unity, forming the basis for Hardy–Weinberg genotype calculations.
Flashcard 20: State the Hardy–Weinberg genotype frequency equation in terms of p and q.
Answer: p2+2pq+q2=1. This equation derives from binomial expansion, predicting genotype frequencies from allele frequencies under equilibrium assumptions.
Flashcard 21: Identify the genotype frequencies under Hardy–Weinberg equilibrium in terms of p and q.
Answer: AA=p2, Aa=2pq, aa=q2. Under random mating, genotype frequencies follow binomial probabilities, with homozygotes as squares and heterozygotes as twice the product.
Flashcard 22: Find q under Hardy–Weinberg if the recessive phenotype frequency is 0.04.
Answer: q=0.2. Recessive phenotype frequency equals q2, so q is the square root, assuming Hardy–Weinberg equilibrium holds.
Flashcard 23: Find p under Hardy–Weinberg if q=0.3 for a two-allele locus.
Answer: p=0.7. Since allele frequencies sum to 1, p is calculated as 1−q for a biallelic locus in equilibrium.
Flashcard 24: Identify the type of selection if heterozygotes have the lowest fitness (both homozygotes favored).
Answer: Disruptive selection (underdominance). When heterozygotes are least fit, selection disrupts intermediates, favoring homozygous extremes and potentially leading to bimodal distributions.
Flashcard 25: What is the key evolutionary consequence of inbreeding on genotype frequencies?
Answer: Increases homozygosity (decreases heterozygosity) without changing allele frequencies. Inbreeding increases mating between relatives, elevating homozygote frequencies via non-random mating while allele frequencies remain unchanged.