Microevolution & Population Genetics (Video Notes)

A set of Q&A flashcards covering key concepts from microevolution and population genetics, including Hardy-Weinberg, evolutionary forces, and Darwinian ideas.

What is evolution?

Change through time; evolution is measured by changes in allele and genotype frequencies in populations across generations; individuals do not evolve.

What is Biological evolution?

Change in allele or genotype frequencies in populations over time; populations evolve, individuals do not.

Adaptive radiation

Rapid diversification from an ancestral species into new resources, challenges, or environmental niches; leads to accumulation of different genotypes and phenotypes.

Microevolution vs. Macroevolution

Microevolution = changes within a species; macroevolution = large‑scale evolutionary patterns over longer timescales.

Population

Group of individuals of the same species living in the same area at the same time that interbreed and share a gene pool.

Gene pool

Sum of all alleles at all gene loci in all individuals within a population; used to identify genotypes and calculate allele frequencies.

Genotype

Genetic makeup of an individual at a locus (e.g., AA, Aa, aa).

Phenotype

Observable appearance and/or function resulting from the interaction of genotype with the environment; part of phenotype is heritable.

Allele frequency (p and q)

p is the frequency of one allele, q is the frequency of the other; for two-allele loci, p + q = 1.

Hardy-Weinberg equilibrium (null model)

Allele and genotype frequencies remain constant from generation to generation in the absence of evolutionary forces (no mutation, migration, selection, drift, and random mating).

Genotype frequencies under Hardy-Weinberg

Predicted frequencies: p^2 for the homozygous dominant, 2pq for the heterozygote, q^2 for the homozygous recessive.

Snapdragon incomplete dominance example (p and q)

An example where p and q (e.g., p=0.7, q=0.3) yield genotype frequencies p^2, 2pq, q^2; used to illustrate allele distribution and predicting offspring genotypes.

Conditions for Hardy-Weinberg equilibrium

No mutations, no gene flow, population size effectively infinite, no natural selection, and random mating.

Mutation

New genetic variants; the ultimate source of new alleles; can be deleterious, neutral, or advantageous; germ-line mutations are heritable.

Gene flow (migration)

Movement of alleles between populations, through individuals or gametes; tends to homogenize populations but can be limited by barriers.

Genetic drift

Random changes in allele frequencies, most pronounced in small populations; reduces genetic variation; includes bottlenecks and founder effects.

Population bottleneck

A drastic reduction in population size that reduces genetic variation and can fix alleles.

Founder effect

A new population started by a few individuals, leading to reduced genetic variation and different allele frequencies from the source population.

Natural selection

Process where inherited traits that confer higher survival or reproductive success become more common over generations; measured by fitness.

Types of natural selection

Directional (favors one extreme), stabilizing (favors intermediates), disruptive (favors extremes).

Relative fitness

An individual's contribution to the gene pool of the next generation relative to others’ contributions.

Sexual selection

A form of natural selection where traits increase mating success, via mate choice or competition; can trade off with survival.

Heterozygote advantage (balancing selection)

Maintains genetic variation; example: Aa is resistant to malaria while AA and aa have different costs; fitness depends on allele frequency.

Balancing selection

Maintenance of genetic diversity through mechanisms like heterozygote advantage and frequency-dependent selection.

Vestigial structures

Useless or reduced structures that reveal evolutionary history.

Darwin and Malthus influence

Malthus argued population growth leads to competition for resources; influenced Darwin’s idea of struggle for survival shaping evolution.

Origin of Species (1859)

Darwin’s landmark book outlining natural selection as the mechanism of evolution.

Descent with modification

Darwin’s idea that species arise from common ancestors through incremental changes over time.

Beagle voyage observations

Fossils, uplift, Galapagos fauna (tortoises, finches, etc.) provided evidence for divergence and common ancestry.

Molecular clock concepts

Rate of genetic change varies by gene; slower in genes under strong negative selection (e.g., histones), faster in pseudogenes; used to estimate divergence times.

Nonrandom mating

Mating that is not random with respect to genotype; can alter genotype frequencies without changing allele frequencies; inbreeding increases homozygosity and may reduce fitness.

Fossil evidence for evolution

Fossils show succession and extinction, supporting descent with modification and historical change over time.

What is evolution?

Change through time; evolution is measured by changes in allele and genotype frequencies in populations across generations; individuals do not evolve.

What is Biological evolution?

Change in allele or genotype frequencies in populations over time; populations evolve, individuals do not.

Adaptive radiation

Rapid diversification from an ancestral species into new resources, challenges, or environmental niches; leads to accumulation of different genotypes and phenotypes.

Microevolution vs. Macroevolution

Microevolution = changes within a species; macroevolution = large

scale evolutionary patterns over longer timescales.

Population

Group of individuals of the same species living in the same area at the same time that interbreed and share a gene pool.

Gene pool

Sum of all alleles at all gene loci in all individuals within a population; used to identify genotypes and calculate allele frequencies.

Genotype

Genetic makeup of an individual at a locus (e.g., AA, Aa, aa).

Phenotype

Observable appearance and/or function resulting from the interaction of genotype with the environment; part of phenotype is heritable.

Allele frequency (p and q)

p is the frequency of one allele, q is the frequency of the other; for two-allele loci, p + q = 1.

Hardy-Weinberg equilibrium (null model)

Allele and genotype frequencies remain constant from generation to generation in the absence of evolutionary forces (no mutation, migration, selection, drift, and random mating).

Genotype frequencies under Hardy-Weinberg

Predicted frequencies: p^2 for the homozygous dominant, 2pq for the heterozygote, q^2 for the homozygous recessive.

Snapdragon incomplete dominance example (p and q)

An example where p and q (e.g., p=0.7, q=0.3) yield genotype frequencies p^2, 2pq, q^2; used to illustrate allele distribution and predicting offspring genotypes.

Conditions for Hardy-Weinberg equilibrium

No mutations, no gene flow, population size effectively infinite, no natural selection, and random mating.

Mutation

New genetic variants; the ultimate source of new alleles; can be deleterious, neutral, or advantageous; germ-line mutations are heritable.

Gene flow (migration)

Movement of alleles between populations, through individuals or gametes; tends to homogenize populations but can be limited by barriers.

Genetic drift

Random changes in allele frequencies, most pronounced in small populations; reduces genetic variation; includes bottlenecks and founder effects.

Population bottleneck

A drastic reduction in population size that reduces genetic variation and can fix alleles.

Founder effect

A new population started by a few individuals, leading to reduced genetic variation and different allele frequencies from the source population.

Natural selection

Process where inherited traits that confer higher survival or reproductive success become more common over generations; measured by fitness.

Types of natural selection

Directional (favors one extreme), stabilizing (favors intermediates), disruptive (favors extremes).

Relative fitness

An individual's contribution to the gene pool of the next generation relative to others’ contributions.

Sexual selection

A form of natural selection where traits increase mating success, via mate choice or competition; can trade off with survival.

Heterozygote advantage (balancing selection)

Maintains genetic variation; example: Aa is resistant to malaria while AA and aa have different costs; fitness depends on allele frequency.

Balancing selection

Maintenance of genetic diversity through mechanisms like heterozygote advantage and frequency-dependent selection.

Vestigial structures

Useless or reduced structures that reveal evolutionary history.

Darwin and Malthus influence

Malthus argued population growth leads to competition for resources; influenced Darwin’s idea of struggle for survival shaping evolution.

Origin of Species (1859)

Darwin’s landmark book outlining natural selection as the mechanism of evolution.

Descent with modification

Darwin’s idea that species arise from common ancestors through incremental changes over time.

Beagle voyage observations

Fossils, uplift, Galapagos fauna (tortoises, finches, etc.) provided evidence for divergence and common ancestry.

Molecular clock concepts

Rate of genetic change varies by gene; slower in genes under strong negative selection (e.g., histones), faster in pseudogenes; used to estimate divergence times.

Nonrandom mating

Mating that is not random with respect to genotype; can alter genotype frequencies without changing allele frequencies; inbreeding increases homozygosity and may reduce fitness.

Fossil evidence for evolution

Fossils show succession and extinction, supporting descent with modification and historical change over time.

What are the main evolutionary forces that drive microevolution?

The main evolutionary forces that drive microevolution are:

1. Mutation: The ultimate source of new alleles, creating new genetic variants.
2. Gene flow (Migration): The movement of alleles between populations.
3. Genetic drift: Random changes in allele frequencies, particularly impactful in small populations.
4. Natural selection: The process where traits that increase survival or reproduction become more common over generations.

What is the role of the Hardy-Weinberg equilibrium principle in understanding evolution?

It serves as a null model to determine if a population is evolving. If observed allele and genotype frequencies significantly deviate from Hardy-Weinberg predictions, it indicates that one or more evolutionary forces (mutation, gene flow, genetic drift, natural selection, nonrandom mating) are acting on the population.