[UCSB SUMMER ‘26] EEMB 2 - Evolution: Final (Cumulative Weeks 1-3)

What is biological evolution?

Genetically based change in a lineage over time; descent with modification.

What is microevolution?

Change in allele frequencies within a population across generations.

What are the five stages of the evolutionary process emphasized in EEMB 2?

Variation → Natural selection → Genetic divergence → Reproductive isolation → Speciation.

Why do populations, not individuals, evolve?

Evolution is defined by changes in population allele frequencies across generations; individuals do not change their inherited allele frequencies during life.

What evidence from biogeography supports evolution?

Related forms occur in different places and many isolated regions contain unique species, consistent with descent plus dispersal and divergence.

What evidence from comparative morphology supports common ancestry?

Homologous and vestigial structures reveal shared underlying body plans inherited from ancestors.

What geological observation supported evolutionary thinking?

Different rock strata contain different fossils, with deeper layers generally representing older life.

Who suggested that land-dwelling human ancestors ultimately came from aquatic ancestors?

Anaximander.

Who recognized fossils as remains/evidence of past life?

Xenophanes.

Who developed Scala Naturae?

Aristotle.

What did Buffon argue about life?

Life was not immutable, environments can influence change, and Earth is old.

What did Erasmus Darwin propose?

Species can change, competition matters, and organisms may share common ancestry.

What did Thomas Malthus show?

Populations can produce more offspring than environments can support; key to the struggle-for-existence idea.

Who developed natural selection and published 'On the Origin of Species'?

Charles Darwin.

Who independently formulated natural selection?

Alfred Russel Wallace.

What is adaptation?

A trait adjustment/change associated with environmental conditions; adaptive variants increase survival and reproduction.

What is an adaptive trait?

Trait form that increases survival and reproduction.

What is a maladaptive trait?

Trait form that reduces survival and reproduction.

What is a neutral trait?

Trait form with no current fitness advantage or disadvantage.

What three broad trait categories vary in populations?

Morphological, physiological, and ethological.

What is discrete variation?

Two or more distinct trait forms.

What is quantitative/continuous variation?

Trait values distributed along a continuum.

What is a gene?

Hereditary DNA unit associated with a trait.

What is an allele?

Alternative molecular form of a gene.

What is a gene pool?

All genes/alleles in a population.

What is a genome?

All genes in a species.

What is a genotype?

An organism's allele set/genetic makeup.

What is a phenotype?

Observable trait expression produced by genotype and environmental influence.

What is the phenotypic frequency equation?

Number with phenotype / total population size; ×100 for percent.

How do you calculate allele A frequency from genotype counts?

p = [2(AA) + Aa] / 2N.

What is the Hardy-Weinberg allele equation?

p + q = 1.

What is the Hardy-Weinberg genotype equation?

p² + 2pq + q² = 1.

What does p² represent?

Expected AA genotype frequency.

What does 2pq represent?

Expected Aa genotype frequency.

What does q² represent?

Expected aa genotype frequency.

What are the five Hardy-Weinberg conditions?

No mutation; very large population; isolation/no gene flow; no fitness differences at the locus; random mating.

What are the three major processes disrupting Hardy-Weinberg equilibrium?

Natural selection, gene flow, genetic drift.

What is genetic equilibrium?

Stable allele frequencies over multiple generations.

If q²=0.09, what is q?

0.30.

If q=0.30, what is p?

0.70.

If p=0.7 and q=0.3, what is the expected heterozygote frequency?

2pq=0.42.

If p=0.7, q=0.3, N=1000, what are the expected AA/Aa/aa counts?

490 AA, 420 Aa, 90 aa.

Which evolutionary process creates new alleles?

Mutation.

What does recombination do?

Creates new combinations of existing alleles; it does not create new alleles.

What is a point mutation?

Small-scale DNA sequence mutation affecting one or a few nucleotides.

What is a chromosomal mutation?

Large-scale mutation affecting chromosome structure or chromosome number.

What is positive assortative mating?

Preferential mating with similar partners; tends to increase homozygosity for the relevant trait.

What is negative assortative mating?

Preferential mating with dissimilar partners; tends to increase heterozygosity.

What is inbreeding?

Mating among relatives; increases homozygosity and expression of deleterious recessives.

What is genetic load?

Deleterious alleles that reduce average fitness.

What is crossbreeding?

Mating among distinct lines/populations, often increasing heterozygosity.

What is hybridization?

Interbreeding among genetically differentiated populations or species.

What are the three types of natural-population variation?

Continuous/normal, polymorphic, and ecogeographic variation.

What is natural selection?

Differential reproductive success among heritable variants that changes genotype/allele frequencies.

What is evolutionary fitness?

Relative genetic contribution of an individual to the next generation.

What is the relative fitness equation?

Reproductive output of genotype / highest reproductive output.

If offspring outputs are 20, 10, 5, what are the relative fitnesses?

1.0, 0.5, 0.25.

Why can the recessive allele persist when selection favors a dominant allele?

When rare, most recessive copies are hidden in heterozygotes and escape selection.

Why can the increase of a recessive allele be slow initially?

A rare recessive allele is expressed in very few homozygotes, so selection has little phenotype to act on.

What is heterozygote advantage?

The heterozygote has higher fitness than either homozygote.

What is balanced polymorphism?

Two or more alleles persist at appreciable frequencies over time.

What is frequency-dependent selection?

Fitness depends on how common or rare a phenotype/genotype is.

What is directional selection?

Favors one phenotypic extreme and shifts the mean.

What is stabilizing selection?

Favors intermediates and selects against extremes.

What is disruptive selection?

Favors both extremes over intermediates.

Why can't selection make perfect organisms?

Historical constraints, trade-offs, changing environments, limited existing variation, and chance processes prevent perfection.

What is coevolution?

Reciprocal evolutionary change between interacting species.

What is the Red Queen hypothesis?

Species must continually evolve to maintain relative fitness against coevolving species.

What is the major benefit of sex?

Recombination creates new allele combinations and helps purge deleterious mutations.

What is the major cost of sex?

Mate-finding and reduced direct genetic contribution compared with clonal reproduction.

What is Muller's Ratchet?

Irreversible accumulation of deleterious mutations in asexual lineages when low-mutation classes are lost.

What is isogamy?

Gametes similar in size/form.

What is anisogamy?

Gametes differ strongly in size, commonly large eggs and small sperm.

What is sexual selection?

Selection caused by differences in mating success.

What is sexual dimorphism?

Sex-specific phenotypic differences.

What is the takeaway from Endler's guppy study?

Predation selects against conspicuous males while mate choice can favor conspicuous coloration; the balance shapes male traits.

What is artificial selection?

Human-directed breeding that changes trait frequencies across generations.

What is genetic divergence?

Accumulation of genetic differences between populations.

What is gene flow?

Movement of alleles among populations via migrants or gametes.

What is the effect of gene flow on divergence?

Generally homogenizes populations and slows divergence.

What is genetic drift?

Random allele-frequency change due to chance sampling.

What is the effect of drift on variation?

Reduces variation and increases homozygosity; can lead to fixation or loss.

Why is drift stronger in small populations?

Sampling error is larger.

What is a sampling error?

An error that occurs when a sample does not represent the population accurately.

What is mutational meltdown?

Accumulation of deleterious mutations lowers fitness, especially in small populations.

What is the bottleneck effect?

Severe population reduction creates an unrepresentative survivor gene pool and amplifies drift.

What is the founder effect?

A few colonists establish a population with allele frequencies unlike the source population.

How does the bottleneck effect differ from the founder effect?

Bottleneck shrinks an existing population; founder effect starts a new population from a small sample.

What is an extinction vortex?

A cycle where small population leads to drift/inbreeding/loss of variation, lowering fitness and leading to further population decline.

What is effective population size?

The number of effective breeders producing the observed genetic drift.

What is the equation for effective population size?

Ne = 4NmNf/(Nm+Nf).

What factors lower effective population size relative to census size?

Skewed sex ratios, unequal reproductive success, and strong fluctuations in breeder numbers.

What is reproductive isolation?

Barriers that reduce gene exchange among diverging populations.

What is a prezygotic barrier?

A barrier that acts before fertilization.

What is a postzygotic barrier?

A barrier that acts after fertilization.

What is ecological isolation?

Different habitats/resources reduce mating encounters.

What is geographic isolation?

Physical separation reduces gene flow.

What is temporal isolation?

Different reproductive times prevent mating.

What is ethological isolation?

Different courtship behaviors/signals prevent mating.

What is mechanical isolation?

Morphological mismatch prevents mating or pollen transfer.