AP Bio Unit 7

Evolution

Change in allele frequencies in a population over time

Population (evolution context)

A group of the same species living in the same area

Why individuals don’t evolve

Only populations evolve because allele frequencies change across generations

Mechanisms of evolution

Processes that change allele frequencies (genetic drift, gene flow, mutation, natural selection, sexual selection)

Genetic drift

Random change in allele frequencies due to chance

When genetic drift is strongest

In small populations

Bottleneck effect

Sudden reduction in population size leading to loss of genetic diversity

Example of bottleneck

Natural disaster leaving few survivors

Founder effect

New population started by a small group with limited genetic variation

Gene flow

Movement of alleles between populations through migration

Effect of gene flow

Increases genetic diversity and reduces differences between populations

Mutation

Random change in DNA sequence

Importance of mutations

Ultimate source of new genetic variation

Natural selection

Individuals with advantageous traits survive and reproduce more

Fitness (evolution)

Reproductive success of an organism

Adaptation

Trait that increases survival or reproduction

Selective pressures

Environmental factors that influence survival (predators, climate, resources)

Sexual selection

Selection based on mating success

Intrasexual selection

Competition within the same sex (e.g., males fighting)

Intersexual selection

One sex chooses mates (e.g., peacock feathers)

Convergent evolution

Unrelated species evolve similar traits

Cause of convergent evolution

Similar environmental pressures

Artificial selection

Humans selectively breed for desired traits

Hardy-Weinberg equilibrium

A model where a population is not evolving

Hardy-Weinberg equation

p^2 + 2pq + q^2 = 1

Meaning of p

Frequency of dominant allele

Meaning of q

Frequency of recessive allele

p + q =

1

Conditions for Hardy-Weinberg

No mutation, no selection, large population, random mating, no gene flow

If conditions are not met

The population is evolving

Small populations vs large populations

Small populations are more affected by drift and environmental change

Molecular evidence of evolution

DNA and protein similarities

Morphological evidence

Physical/anatomical similarities

Homologous structures

Same structure, different function, common ancestry

Vestigial structures

Reduced structures with little or no function

Analogous structures

Same function, different origin, no common ancestry

Geological evidence

Fossil record shows change over time

Geographical evidence (biogeography)

Species distribution patterns across locations

Speciation

Formation of new species

Allopatric speciation

Speciation due to geographic isolation

Sympatric speciation

Speciation without geographic separation

Reproductive isolation

Barriers that prevent species from interbreeding

Prezygotic barriers

Prevent fertilization (behavioral, temporal, mechanical, gametic)

Postzygotic barriers

Occur after fertilization (hybrid inviability, sterility)

Biological species concept

Species can interbreed and produce fertile offspring

Phylogeny

Evolutionary history of a species or group

Phylogenetic tree

Diagram showing evolutionary relationships

Node (tree)

Common ancestor

Branch (tree)

Evolutionary lineage

Outgroup

Least closely related group used for comparison

Shared derived characteristics

Traits unique to a particular group

Trait gain/loss in evolution

Traits can appear or disappear over time

Molecular vs morphological data

Molecular data is more reliable; morphology can be misleading due to convergent evolution

Common ancestry of eukaryotes

All eukaryotes share a common ancestor

Miller-Urey experiment

Simulated early Earth conditions and produced organic molecules

Meteorite theory

Organic molecules came from space

Deep-sea vent theory

Life originated near hydrothermal vents

RNA world hypothesis

RNA was the first genetic material and could store information and catalyze reactions

Extinction

Permanent loss of a species

Causes of extinction

Environmental change, habitat loss, competition, disease, catastrophic events

Human causes of extinction

Habitat destruction, pollution, climate change, overhunting

Biodiversity

Variety of life in an ecosystem

Speciation rate

Rate at which new species form

Extinction rate

Rate at which species disappear

Effect of extinction on niches

Extinction opens niches for new species (adaptive radiation)