bio vocab

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Natural Selection and Evolution of Populations

  • Population: A group of individuals of the same species that interbreed.

  • Gene Pool: All the genes (alleles) of all members of a population.

  • Evolution (Genetic Terms): Any change in the relative frequency of alleles in a population.

Important Vocabulary

  • Mutations: Changes in DNA sequences; beneficial mutations increase in the population.

  • Recombination: Genes combine in new ways during gamete production and crossing over (meiosis).

  • Gene Flow: Transfer of genes between populations (e.g., migration).

3 Main Sources of Genetic Variation

  1. Mutations

  2. Recombination

  3. Gene Flow

Natural Selection

  • Acts on populations, not individual organisms.

  • Single-Gene Traits: Can lead to changes in allele frequencies (e.g., polydactylism).

  • Polygenic Traits: Controlled by multiple genes, resulting in more phenotypes and bell curves.

Types of Natural Selection

  1. Directional Selection: Higher fitness at one end of the curve (e.g., anteaters with longer tongues).

  2. Stabilizing Selection: Higher fitness at the center of the curve (e.g., human baby birth weight).

  3. Disruptive Selection: Higher fitness at both ends of the curve (e.g., bird beak sizes).

Genetic Drift

  • Definition: Random changes in allele frequencies due to chance, not natural selection.

  • Founder Effect: Allele frequencies change due to migration of a subgroup.

  • Bottleneck Effect: Sharp reduction in population size due to environmental or human factors.

Genetic Equilibrium

  • Definition: Allele frequencies remain constant if these 5 conditions are met:

    1. Random mating

    2. Very large population

    3. No migration

    4. No mutations

    5. No natural selection

Speciation

  • Definition: Formation of a new species.

  • Species: Organisms that can interbreed and produce fertile offspring.

  • Reproductive Isolation: Prevents interbreeding between populations.

3 Types of Reproductive Barriers

  1. Behavioral Isolation: Differences in courtship or behavior (e.g., meadowlark songs).

  2. Geographic Isolation: Physical barriers separate populations (e.g., Grand Canyon squirrels).

  3. Temporal Isolation: Reproductive timing differences (e.g., plants flowering at different times).

Patterns in Evolution

  • Extinction: Over 90% of all species are extinct; modern extinction is often human-caused.

  • Divergent Evolution (Adaptive Radiation): Related species become dissimilar due to different environments (e.g., red vs. kit fox).

  • Convergent Evolution: Unrelated species develop similar traits due to similar environments (e.g., cacti in American and African deserts).

  • Coevolution: Two species evolve in response to each other.

    • Cooperative: Seen in symbiotic relationships.

    • Opposition: Includes camouflage and defense mechanisms.

Rates of Evolution

  • Gradualism: Slow, steady change.

  • Punctuated Equilibrium: Sudden, rapid change (e.g., volcanic eruption and pocket mice).

Phylogenies and Evolutionary Classification

  • Phylogeny: Evolutionary relationships among organisms.

    • Root: Ancestral lineage.

    • Tips of Branches: Descendants of the ancestor.

    • Branching: Speciation events.

  • Cladistic Analysis: Focuses on derived characteristics (traits appearing in recent lineage parts).