Population Genetics — Quick Notes

Variation exists for traits within a population; selection acts on this variation.
Fitness: differential reproductive success among phenotypes.
Directional selection: one phenotype is favored, increasing its frequency in the next generation, often shifting the distribution toward an extreme and potentially leading toward speciation.
Stabilizing selection: intermediate/average trait values have higher fitness, reducing variation in the population.
Population bottleneck: a sharp reduction in population size due to an event, causing a loss of genetic diversity.
Founder effect: a new population is founded by a small group, so the new gene pool reflects only the founders' alleles (random sampling).
Ecological example (oak gall): a tree forms a protective gall around a developing insect/larva inside it.

Definition: one phenotype is favored, producing higher fitness and a shift in the population mean toward that phenotype.
Visualization note: original population distribution (blue) vs post-selection distribution (red).
Outcome: tends to drive evolutionary change and can contribute to speciation.

Definition: individuals with average trait values have higher fitness.
Effect: reduces variance around the mean; the population mean remains relatively stable.

Event causes a drastic drop in population size, reducing genetic diversity.
Example discussed: northern elephant seals underwent a bottleneck due to intense poaching.
Note: bottlenecks are related to broader evolutionary mechanisms like the founder effect.

Subset of a population moves to a new environment, founding a new population.
The new population's allele pool consists largely of the founders' alleles.
Randomness: which alleles the founders carry determines the new population's genetic composition.

Insect/larva becomes encased in a gall formed by the tree.
The gall provides protection as the larva develops inside; later the larva exits.

Distinguish directional vs stabilizing selection by which phenotypes have higher fitness and how the distribution changes.
Recognize bottlenecks and founder effects as processes that alter genetic variation and allele frequencies in populations.
Use the oak gall example as a case of plant–insect interaction that affects organismal development and defense mechanisms.