Unit 7 AP Bio

🔹 Topic 1: Natural Selection

Key Concepts:

• Natural selection is the process by which traits that enhance survival and reproduction become more common in successive generations.

• Causes of natural selection: Overproduction of offspring, variation among individuals, competition for resources, and differential survival and reproduction.

• Phenotypic variation provides the raw material for natural selection; individuals with traits better suited to the environment tend to survive and reproduce.

• Humans affect diversity through artificial selection, habitat destruction, pollution, and introduction of invasive species.

• Environmental changes apply selective pressures, changing allele frequencies in a population.

Example Questions:

• Which of the following best explains how natural selection can lead to evolution? (A) Individuals evolve over time, (B) Environments create new traits, (C) Individuals with advantageous traits are more likely to reproduce, (D) All mutations are harmful.

🔹 Topic 2: Evolution of Populations

Key Concepts:

• Mutation, genetic drift, gene flow, and natural selection change allele frequencies over time.

• Genetic drift has greater effects in small populations and includes:

  • Bottleneck effect: A drastic reduction in population size causes loss of genetic diversity.

  • Founder effect: A small group starts a new population with a different allele frequency than the original.

• Gene flow introduces or removes alleles through migration.

• Hardy-Weinberg Equilibrium (no evolution):

  1. Large population

  2. No migration

  3. No mutations

  4. Random mating

  5. No natural selection

• Equation: p² + 2pq + q² = 1; p + q = 1

  • p - dominant allele

  • q - recessive allele

  • 2pq - heterozygous

Example Questions:

• Which condition would violate Hardy-Weinberg equilibrium? (A) No selection, (B) Random mating, (C) Mutation, (D) Large population size

🔹 Topic 3: Evidence of Evolution and Phylogeny

Key Concepts:

• Evidence for evolution:

  • Fossil record (shows gradual changes over time)

  • Morphological homologies (shared structures)

  • Molecular homologies (DNA/protein sequence similarities)

• Common ancestry of eukaryotes:

  • Membrane-bound organelles

  • Linear chromosomes

  • Genes with introns

• Ongoing evolution: Pathogen resistance, observable genetic shifts in populations

• Cladograms/phylogenetic trees:

  • Show evolutionary relationships

  • Constructed using shared derived traits or molecular data

  • Nodes represent common ancestors

  • Outgroup is used for comparison

Example Questions:

• Which of the following supports the theory of common ancestry? (A) Similar climate tolerance, (B) Analogous traits, (C) Shared genetic code, (D) Different protein functions

🔹 Topic 4: Speciation & Extinction

Key Concepts:

• Speciation happens when populations become reproductively isolated.

  • Allopatric speciation: Physical barrier

  • Sympatric speciation: Genetic or behavioral isolation

• Reproductive isolation:

  • Prezygotic barriers (habitat, temporal, behavioral, mechanical, gametic)

  • Postzygotic barriers (hybrid inviability, sterility)

• Rates of speciation:

  • Gradualism (slow changes)

  • Punctuated equilibrium (short bursts of change)

• Extinction:

  • Can occur due to environmental change, loss of genetic diversity, or human activity

  • Leads to adaptive radiation—rapid speciation as niches open

Example Questions:

• Which situation most likely results in sympatric speciation? (A) Migration, (B) A river divides a population, (C) Polyploidy in plants, (D) Climate change

🔹 Topic 5: Origin of Life

Key Concepts:

• Earth formed ~4.6 bya; earliest life ~3.5 bya

• Abiotic synthesis hypothesis:

  • Early Earth had the conditions to form organic molecules

  • No oxygen allowed for complex molecules to form

• RNA World Hypothesis:

  • RNA was likely the first genetic material—can store, replicate, and catalyze reactions

• Scientific evidence includes:

  • Geological dating

  • Miller-Urey experiment (formed amino acids from early Earth gases)

  • Meteorites as a source of organic molecules that provide insights into the building blocks of life and suggest that the components necessary for life may have originated from extraterrestrial sources.