AP Biology Unit 7: Mechanisms of Microevolution

Population Genetics

The study of how genetic principles apply to entire populations, focusing on allele frequencies.

Population

A localized group of individuals capable of interbreeding and producing fertile offspring.

Gene Pool

The aggregate of all copies of every type of allele at all loci in every individual in a population.

Fixed Allele

Occurs if all members of a population are homozygous for the same allele, meaning only one allele exists for that gene.

Microevolution

A change in allele frequencies in a population over generations; the smallest scale of evolution.

Hardy-Weinberg Principle

Describes a hypothetical, non-evolving population and serves as a null hypothesis for evolutionary biologists.

Five Conditions for Hardy-Weinberg Equilibrium

1) No Mutation; 2) Random Mating; 3) No Natural Selection; 4) Extremely Large Population Size; 5) No Gene Flow.

Pinky (Small)

Represents small populations leading to Genetic Drift.

Allele Frequencies Formula

The equation p + q = 1, where p is the dominant allele frequency and q is the recessive allele frequency.

Genotype Frequencies Formula

The equation p² + 2pq + q² = 1, representing the frequencies of homozygous dominant, heterozygous, and homozygous recessive individuals.

Genetic Drift

Unpredictable fluctuations in allele frequencies, most significant in small populations, reducing genetic variation.

Founder Effect

Occurs when a few individuals from a larger population establish a new population with a gene pool not reflective of the original.

Bottleneck Effect

Occurs when a sudden environmental change drastically reduces a population's size, impacting allele representation.

Gene Flow

The transfer of alleles into or out of a population due to the movement of individuals or their gametes.

Mutation

A change in the nucleotide sequence of an organism's DNA; the ultimate source of new alleles.

p (dominant allele frequency)

The frequency of the dominant allele in the population.

q (recessive allele frequency)

The frequency of the recessive allele in the population.

p²

Frequency of homozygous dominant individuals (AA) in a population.

2pq

Frequency of heterozygous individuals (Aa) in a population.

q²

Frequency of homozygous recessive individuals (aa) in a population.

Real Populations and Hardy-Weinberg Equilibrium

Real populations are rarely in Hardy-Weinberg equilibrium; the model helps demonstrate if evolution is occurring.

Common Mistakes with p and q

Confusing p with p² or q with q²; always start by solving for q² if given phenotypic data.

Dominance and Frequency

Dominant alleles are not necessarily the most common; dominance refers to expression, not evolutionary fitness.

Misinterpreting Hardy-Weinberg Equilibrium

Assuming a population must be in equilibrium; real populations usually deviate from expected values.

Memory Aid for Evolution Conditions

Map the conditions that cause evolution to your hand for easy recall: Pinky (Small), Ring (Non-random mating), Middle (Mutation), Pointer (Gene Flow), Thumb (Natural Selection).