EVOLUTION (NATURAL SELECTION, DRIFT, MICROEVOLUTION, HARDY–WEINBERG)

What is evolution in biological terms?

A change in allele frequencies in a population over generations.

What is microevolution?

Evolutionary change within populations over short timescales (changes in allele frequencies).

What is macroevolution?

Large-scale evolutionary patterns such as speciation and extinction.

What is a population?

A group of interbreeding individuals of the same species living in the same area.

What is a gene pool?

All alleles present in a population at a given time.

What is allele frequency?

The proportion of a particular allele in a population’s gene pool.

What is genotype frequency?

The proportion of each genotype in a population.

What is natural selection?

A process where individuals with advantageous heritable traits have higher fitness and leave more offspring.

What is fitness?

An organism’s reproductive success relative to others in the population.

What are the requirements for natural selection?

Variation, heritability of traits, differential reproductive success.

Does natural selection act on individuals or populations?

Acts on individuals, but changes allele frequencies in populations.

What is directional selection?

Selection that favors one extreme phenotype, shifting the population mean.

What is stabilizing selection?

Selection that favors intermediate phenotypes, reducing variation.

What is disruptive selection?

Selection favoring both extremes, increasing variation and possibly leading to speciation.

What is balancing selection?

Selection that maintains multiple alleles in a population (e.g., heterozygote advantage).

What is frequency-dependent selection?

Fitness of a phenotype depends on how common or rare it is in the population.

What is genetic drift?

Random changes in allele frequencies due to chance events.

When is genetic drift strongest?

In small populations.

What is the bottleneck effect?

A drastic reduction in population size leading to loss of genetic diversity.

What is the founder effect?

When a few individuals start a new population with different allele frequencies than the original population.

Why is drift non-adaptive?

It changes allele frequencies randomly, not based on fitness.

What is fixation?

When an allele reaches a frequency of 100% in a population.

How does drift affect rare alleles?

Rare alleles are more likely to be lost by chance.

What is gene flow?

Movement of alleles among populations via migration or gamete transfer.

How does gene flow affect populations?

It homogenizes populations, reducing differences between them.

How can gene flow oppose natural selection?

It can introduce alleles that reduce fitness in the local environment.

What are mutations in evolution?

Random changes in DNA that introduce new genetic variation.

Are mutations usually beneficial?

Most are neutral or deleterious; beneficial mutations are rare but important for adaptation.

What role do mutations play in evolution?

They are the ultimate source of new alleles.

What is nonrandom mating?

Mating based on phenotype or relatedness rather than chance.

What is assortative mating?

Individuals preferentially mate with similar phenotypes.

What does inbreeding cause?

Increases homozygosity and exposes deleterious recessive alleles.

What is the Hardy-Weinberg equilibrium principle?

Allele and genotype frequencies remain constant from generation to generation if no evolutionary forces act.

What are the Hardy-Weinberg assumptions?

No mutation, no migration, no natural selection, random mating, infinitely large population.

What is the equation for allele frequencies in HW?

p + q = 1.

What is the equation for genotype frequencies in HW?

p² + 2pq + q² = 1.

What does p² represent?

Frequency of homozygous dominant genotype.

What does q² represent?

Frequency of homozygous recessive genotype.

What does 2pq represent?

Frequency of heterozygotes.

How do you calculate q from recessive phenotype frequency?

q = sqrt(recessive phenotype frequency).

When is a population said to be evolving at a locus?

When observed genotype frequencies differ from expected HW frequencies.

What is a chi-square test used for in population genetics?

To determine whether observed genotype frequencies differ significantly from Hardy-Weinberg expectations.

What does a significant chi-square value indicate?

The population is NOT in Hardy-Weinberg equilibrium at that locus.

What does a non-significant chi-square value indicate?

No evidence of evolution at that locus; population fits HW expectations.

Why are degrees of freedom important in chi-square?

They determine the critical value needed to assess significance.

What is sexual selection?

A form of natural selection where certain traits increase mating success.

What is intersexual selection?

Mate choice, often females choosing males.

What is intrasexual selection?

Competition among individuals of one sex for access to mates.

Why can sexual selection produce traits that reduce survival?

Because mating advantages outweigh survival costs.

What is adaptive evolution?

Evolution that increases average fitness of a population.

What is local adaptation?

When populations evolve traits that increase fitness in their specific environments.

Why do different populations of the same species often evolve differently?

Different environments impose different selective pressures.

What is a cline?

A gradual change in a trait or allele frequency across a geographic gradient.

What is genetic variation?

Differences among individuals in DNA and phenotypes.

What maintains genetic variation in populations?

Mutation, gene flow, balancing selection, diploidy, heterozygote advantage.

What is heterozygote advantage?

When heterozygotes have higher fitness than either homozygote.

What famous example demonstrates heterozygote advantage?

Sickle-cell allele conferring malaria resistance in heterozygotes.

What is neutral variation?

Genetic variation that does not affect fitness.

What happens if all HW assumptions hold?

Allele frequencies remain constant (no evolution).

What is the main purpose of HW equilibrium?

It provides a null model to detect when evolutionary forces are acting.