Chapter 19: The Evolution of Populations Flashcards
Define population genetics and explain its role in evolutionary biology.
Study of genetic variation within populations and how allele frequencies change over time.
Significance: Connects Mendelian inheritance with Darwinian evolution, explaining mechanisms like natural selection and genetic drift.
What is the Hardy-Weinberg equilibrium? List its five assumptions.
Equation: p² + 2pq + q² = 1 (where p and q are allele frequencies).
Assumptions:
1. No mutations.
2. Random mating.
3. No natural selection.
4. Extremely large population size.
5. No gene flow.
Calculate allele frequencies if 16% of a population exhibits a recessive phenotype.
q² = 0.16 → q = 0.4.
p = 1 − q = 0.6.
Genotype frequencies:
Dominant homozygotes (p²): 0.36.
Heterozygotes (2pq): 0.48.
Recessive homozygotes (q²): 0.16.
Contrast genetic drift and gene flow. Provide examples.
Genetic drift: Random allele frequency changes (e.g., bottleneck effect in cheetahs; founder effect in Amish populations).
Gene flow: Allele transfer between populations (e.g., pollen carried by wind to neighboring plants).
Describe directional, stabilizing, and disruptive selection with examples.
Directional: Favors one extreme phenotype (e.g., antibiotic resistance in bacteria).
Stabilizing: Favors intermediate traits (e.g., human birth weight).
Disruptive: Favors both extremes (e.g., black-bellied seedcrackers with small/large beak sizes).
What are the primary sources of genetic variation in populations?
Mutations: New alleles arise from DNA changes.
Sexual reproduction: Crossing over and independent assortment during meiosis.
Gene flow: Introduces alleles from other populations.
How does natural selection drive adaptive evolution?
Traits enhancing survival/reproduction become more common (e.g., camouflage in peppered moths during industrialization).
Compare prezygotic and postzygotic barriers to reproduction.
Prezygotic: Prevent fertilization (e.g., temporal isolation in mating seasons of coral species).
Postzygotic: Reduce hybrid viability/fertility (e.g., mule sterility).
How does sympatric speciation differ from allopatric speciation?
Allopatric: Geographic isolation (e.g., Grand Canyon squirrels).
Sympatric: Speciation without geographic barriers (e.g., polyploidy in plants like Tragopogon).
Explain how the peppered moth (Biston betularia) illustrates natural selection.
Pre-industrial: Light-colored moths dominated (camouflage on lichen-covered trees).
Post-industrial: Soot darkened trees → dark moths (melanic form) survived predation better.
How does antibiotic resistance demonstrate evolution in action?
Overuse of antibiotics selects for resistant bacterial strains (e.g., MRSA with mecA gene mutations).
What is sexual selection, and how does it differ from natural selection?
Sexual selection: Traits improve mating success (e.g., peacock tail feathers).
Natural selection: Traits improve survival.
Define fitness in evolutionary terms.
An organism’s ability to survive and reproduce, measured by its contribution to the gene pool.
Design an experiment to test Hardy-Weinberg equilibrium in a wild plant population.
Collect DNA samples from 500+ plants.
Genotype for a neutral locus (e.g., flower color).
Calculate observed vs. expected genotype frequencies.
Use chi-square test to determine if deviations are statistically significant.
