4. Evolution of Populations - Lecture Note

Flashcards covering Hardy-Weinberg equilibrium, mechanisms of evolution, genetic drift, natural selection modes, balancing selection, and related concepts from the notes.

What are the five conditions for Hardy-Weinberg equilibrium?

No mutation; no gene flow; random mating; very large population; no selection.

What is the significance of Hardy-Weinberg equilibrium?

Natural populations can evolve at some gene loci while being in equilibrium at others.

Name the five mechanisms of evolution that change allele frequencies.

Mutation, gene flow, nonrandom mating, genetic drift, and natural selection.

What is the ultimate source of genetic variation?

Mutation (including chromosomal rearrangements and gene duplication).

What is the effect of crossing over during meiosis I (prophase I)?

Generates new allele combinations, increasing genetic variation.

What is the effect of random assortment during metaphase I?

Produces random combinations of maternal and paternal chromosomes in gametes.

What is the effect of random fertilization?

Any egg can be fertilized by any sperm, creating diverse offspring.

What is genetic drift?

Random fluctuations in allele frequencies, more pronounced in small populations; includes founder and bottleneck effects.

What is the founder effect?

Allele frequencies in a new population founded by a small group differ from the original population.

What is the bottleneck effect?

Drastic reduction in population size that reduces genetic variation and changes allele frequencies among survivors.

What is gene flow?

Movement of alleles between populations; tends to homogenize allele frequencies.

What is nonrandom mating?

Inbreeding or assortative mating; does not change allele frequencies but changes genotype frequencies; inbreeding lowers heterozygotes.

What are the three modes of natural selection?

Directional selection, disruptive selection, stabilizing selection.

What conditions are required for natural selection to increase allele frequencies?

Variation exists, is genetically inherited, and leads to greater reproductive success in the next generation.

What is directional selection?

Favors individuals at one extreme, shifting allele frequencies in one direction.

What is disruptive selection?

Favors extreme phenotypes over intermediate, increasing variation.

What is stabilizing selection?

Favors intermediate phenotypes, reducing variation.

What is balancing selection?

Maintains variation in a population, including heterozygote advantage and frequency-dependent selection.

What is heterozygote advantage?

Heterozygotes have higher fitness than either homozygote, helping maintain certain alleles (example: sickle-cell allele in malaria regions).

What is frequency-dependent selection?

Fitness of a phenotype depends on its frequency in the population.

What is sexual selection?

A form of natural selection that acts on mating success and can produce sexual dimorphism.

Can natural selection interact with other evolutionary forces?

Yes; it can interact with genetic drift and gene flow among others.

Why is there no goal in evolution?

Evolution has no predefined goal; natural selection operates with limits and is not purposeful.

What is the small population effect in genetic drift?

Stronger random allele frequency changes occur as population size decreases.

What is inbreeding and its effect on allele vs genotype frequencies?

Inbreeding reduces heterozygote frequency but does not change allele frequencies.

What other genetic changes contribute to variation besides point mutations?

Chromosomal rearrangements and gene duplications.