How Populations Evolve

See separate FlexArt PowerPoint slides for figures and tables.
Exam 5 Topics: - 16.1 Genes, Populations, and Evolution - 16.2 Natural Selection - 16.3 Maintenance of Diversity

Rank your knowledge: 1 (least) - 5 (expert).
Goals for post-lecture: - Explain evolution in populations and allele frequency changes. - List five conditions necessary for Hardy-Weinberg equilibrium. - Apply Hardy-Weinberg principle for estimating genotype frequencies. - Describe agents of evolutionary change.

Population Definition: A group of organisms of a single species in a specific area at the same time.
Diversity: Exists among population members.
Population Genetics: Studies diversity in terms of allele differences, including genotype and phenotype frequencies over time.

Definition: Evolutionary changes within populations.
Gene Pool: Collection of all alleles in a population; described in terms of: - Genotype Frequencies - Allele Frequencies

Definition: Proportion of each allele within a population's gene pool.
Relationship: Frequencies of dominant and recessive alleles sum to 1: - $p + q = 1$ - Where $p$ is the frequency of one allele and $q$ is the frequency of the other.
Changes in allele frequencies over time signify microevolution.

Definition: A principle stating that allele frequencies in a population remain constant under specific conditions: - Conditions: - No mutation. - No migration. - Large gene pool. - Random mating. - No selection. - Consequence of Deviation: Indicates that evolution has occurred.

Example with 25 moths, 50 alleles: - Allele counts: D = 10, d = 40. - Genotype frequencies calculation using: - $p = rac{10}{50} = 0.20$ (frequency of D) - $q = rac{40}{50} = 0.80$ (frequency of d) - Genotype probabilities: - $p^2 = 0.04$ (frequency of DD) - $2pq = 0.32$ (frequency of Dd) - $q^2 = 0.64$ (frequency of dd)
Total must equal 1: - $p^2 + 2pq + q^2 = 1$

Mutation: Provides new alleles; not all mutations are adaptive. - Example: Color mutations in peppered moths.
Gene Flow (Migration): Movement of alleles between populations; can reduce genetic divergence.
Genetic Drift: Changes in allele frequencies due to random sampling; occurs prominently in small populations. - Effects: - Bottleneck Effect: Majority of individuals are prevented from entering the next generation. - Founder Effect: New populations started from a small group; leads to changes in allele frequencies.

Definition: Individuals do not mate randomly. - Types: - Assortative mating: Choose similar phenotypes. - Consequences: Increases homozygosity; can impact population evolution. - Example: Increased frequency of color blindness on Pingelap Island.

Definition: Adaptation of populations to their environment.
Requirements: - Variation among population members. - Inheritance of traits. - Differential adaptiveness impacting survival. - Differential reproduction based on adaptability.

Stabilizing Selection: Intermediate phenotypes favored; reduces variance. - Example: Human birth weight.
Directional Selection: Extreme phenotypes favored; shifts phenotypic distribution. - Example: Antibiotic resistance in bacteria.
Disruptive Selection: Extreme phenotypes favored over intermediates; can create two peaks. - Example: Variability in British land snails.

Adaptive changes in males and females enhance reproductive success.
Female Choice: Females select mates based on fitness traits (e.g., good genes hypothesis, runaway hypothesis).
Male Competition: Males compete aggressively for mating opportunities. - Cost-benefit analysis of mating competition.

Populations with limited variation struggle to adapt to new conditions; variability is key.
Environment's Role: Differential selection based on ecological factors maintains diversity. - Example: Beak size variation in Galápagos finches based on food availability.

Definition: Maintains genetic variations; provides benefits to heterozygotes in certain conditions. - Example: Sickle-cell allele in malaria-prone regions: - Heterozygotes (HbAHbS) have vitality against malaria while homozygotes for the allele often succumb to disease.
Consequences: High frequency in malaria-prone populations enhances survival prospects of heterozygotes. - Genotype outcomes: - HbAHbA: Normal phenotype but dies from malaria. - HbAHbS: Sickle-cell trait; lives due to malaria resistance. - HbSHbS: Sickly phenotype; dies from sickle-cell disease.

Evolutionary changes in populations are quantified through allele frequency shifts.
Hardy-Weinberg conditions must be satisfied for equilibrium; deviations indicate evolution.
Microevolution mechanisms include genetic drift, mutation, and migration, with significant impact on allele distributions.
Natural selection shapes species through various selection types, operating based on environmental interactions and reproductive success.
Genetic diversity is essential for adaptability and survival; mechanisms such as heterozygote advantage illustrate the complexity of gene interplay within populations.