Evolution Midterm

What is mutation?

A change in DNA sequence that creates new genetic variants (new alleles).

Why are mutations important evolutionarily?

They are the ultimate source of all new genetic variation.

Define point mutation.

Change in a single nucleotide (base substitution).

Define insertion mutation.

Addition of one or more nucleotides.

Define deletion mutation.

Removal of one or more nucleotides.

What is gene duplication?

Copying of a gene, providing raw material for new functions.

Why is gene duplication considered the major source of new functional genes?

One copy keeps original function while the other can evolve new roles (neofunctionalization or subfunctionalization).

What is chromosomal inversion?

A chromosome segment flips orientation, altering gene order.

What is whole genome duplication (WGD)?

Duplication of all chromosomes.

Categories of mutation effects on fitness?

Lethal, deleterious, neutral, beneficial.

What did Peris et al. show about point mutations?

Most mutations are neutral or slightly deleterious; few are beneficial.

Phenotype vs genotype?

Phenotype = observable trait.
Genotype = genetic makeup.

What is heritability?

Proportion of trait variation due to genetic differences.

How does environment affect phenotype?

Same genotype can produce different phenotypes depending on environment.

Two steps of gene expression?

Transcription (DNA → mRNA) and Translation (mRNA → protein).

Hardy–Weinberg principle?

Allele frequencies remain constant unless evolutionary forces act.

HWE equation?

p² + 2pq + q² = 1 ; p + q = 1

Five assumptions of HWE?

No selection, no mutation, large population, no migration, random mating.

Two main uses of HWE?

1. Calculate genotype/allele frequencies

2. Test whether evolution is occurring

What does it mean if observed ≠ expected genotype frequencies?

The population is evolving.

What is fitness?

Reproductive success relative to others.

When does natural selection occur?

When genotypes differ in survival or reproduction.

What is adaptation?

Trait shaped by natural selection that increases fitness.

Why don’t deleterious recessive alleles reach zero frequency?

They hide in heterozygotes

Difference between deleterious vs lethal recessive alleles?

Deleterious reduces fitness; lethal causes death in homozygotes.

Which beneficial alleles increase fastest: dominant, additive, or recessive?

Additive fastest overall; dominant rises quickly early; recessive is slowest.

Why are recessive beneficial alleles slow to spread?

Selection can’t “see” them when rare (hidden in heterozygotes).

What is genetic drift?

Random changes in allele frequencies due to chance events in reproduction or death.

Is drift adaptive?

No — it is random.

What happens to alleles under drift?

They may become fixed (freq = 1) or lost (freq = 0).

How does population size affect drift?

Drift is stronger in small populations.

In small populations, allele frequency fluctuations are _____.

Larger.

In small populations, probability of allele loss is _____.

Higher.

Alleles near frequency 0 or 1 are more likely to be _____.

lost or fixed.

Founder effect?

New population started by few individuals → reduced genetic diversity.

Bottleneck?

Sudden population crash → loss of genetic diversity.

Example of bottleneck in lecture?

Northern elephant seals.

How does bottleneck affect fitness long-term?

Reduced diversity → reduced fitness and adaptability.

What is gene flow?

Movement of alleles between populations via migration.

Effect of high gene flow?

Populations become genetically similar.

Effect of low gene flow?

Populations diverge genetically.

Genetic diversity vs genetic structure?

Diversity = variation within populations.
Structure = differences among populations.

Three measures of genetic diversity?

Heterozygosity, allelic richness, nucleotide diversity.

What drives population genetic structure?

Gene flow, drift, founder effects, bottlenecks, history, geography.

Isolation by distance means?

Genetic distance increases with geographic distance.

What is FST?

Measure of genetic differentiation between populations.

What does high FST indicate?

Strong population structure (little gene flow).

PCA plots show what?

Clustering of individuals based on genetic similarity.

Structure plots show what?

Each individual’s ancestry proportions.

Channel Island fox example shows?

Strong drift + isolation → very low diversity and strong structure.

Definition of evolution?

Change in heritable traits across generations.

List 4 applied reasons we study evolution.

Antibiotic resistance, epidemiology, cancer, conservation.

Why is evolution important for medicine?

Pathogens evolve (antibiotics, viruses, cancer cells).

Why is evolution important for conservation?

Determines whether species can adapt to climate change.

Evolution occurs when…

Some genotypes leave more offspring than others.

What evolutionary forces mainly shaped Channel Island fox populations?

Founder effects, bottlenecks, genetic drift, and isolation (low gene flow).

Why do island foxes have much lower genetic diversity than mainland grey foxes?

Small founding populations + long-term isolation caused strong drift and allele loss.

What does high FST among island fox populations indicate?

Strong genetic structure and little gene flow between islands.

What does the structure plot of island foxes show?

Each island forms its own distinct genetic cluster.

Main takeaway from Channel Island fox case study?

Small, isolated populations rapidly lose genetic diversity and become highly structured.

What happened to Northern elephant seals historically?

Severe population bottleneck due to overhunting.

Did elephant seal population size recover?

Yes — numbers rebounded, but genetic diversity did NOT fully recover.

How do Northern vs Southern elephant seals differ genetically?

Northern seals have much lower heterozygosity and nucleotide diversity.

Why doesn’t population recovery restore genetic diversity?

Lost alleles during bottleneck cannot be recreated (unless by new mutation).

What organism was used to study effects of point mutations on fitness?

A bacteriophage (virus) that infects E. coli.

What does the distribution of mutation effects look like?

Skewed heavily toward small negative effects, with rare positive effects.

What organism showed different morphologies with the same genotype?

Daphnia.

What environmental factor changed Daphnia morphology?

Predator cues during development.

Why must flu vaccines be updated every year?

Influenza evolves rapidly via mutation and selection.

Peppered moth case study demonstrates which evolutionary mechanism?

Natural selection.

Environmental change in the peppered moth case?

Industrial pollution darkened tree bark and killed lichens.

Trait under selection in peppered moths?

Wing color (light vs dark morph).

Selective agent in the peppered moth study?

Bird predation.

Which morph was favored before the Industrial Revolution?

Light morph.

Which morph was favored after pollution increased?

Dark morph.

Why did dark moths increase in polluted forests?

Better camouflage → higher survival → higher reproduction.

What caused morph frequencies to change over time?

Differential survival and reproduction

Peppered moth = example of what type of selection?

Directional selection.

What did Kettlewell’s experiments suggest?

Survival differed between morphs depending on environment.

What did Majerus later confirm?

Birds were the true selective agent.

What happened to Florida panther population size in the 1990s?

Dropped to ~20–30 individuals.

Florida panther case mainly illustrates which forces?

Genetic drift and inbreeding.

Why did genetic problems increase as population shrank?

Small populations lose alleles and become more homozygous.

What is cryptorchidism in panthers?

Undescended testes causing sterility.

What heart problem appeared in Florida panthers?

Atrial septal defects.

These defects increased because of what genetic process?

Inbreeding.

Why can harmful recessive traits increase in small populations?

Drift + inbreeding expose homozygous recessives.

What is the extinction vortex?

Small population → low fitness → smaller population → repeat.

Why is genetic drift stronger in Florida panthers?

Very small population size.

Conservation solution used for Florida panthers?

Introduced Texas cougars.

Introducing Texas panthers added what evolutionary force?

Gene flow.

Purpose of introducing Texas panthers?

Increase genetic diversity and fitness (genetic rescue).

STRUCTURE plot after introduction showed what? (panthers)

Mixed ancestry between Florida and Texas panthers.

Did introductions help Florida panthers?

Yes — increased heterozygosity and reduced defects.