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Hardy-Weinberg & Pop Genetics
Mechanisms of Evolution
Natural Selection
Speciation & Barriers
Phylogeny & Evidence
100
A diploid sample has 20 AA, 50 Aa, and 30 aa individuals. Calculate the frequencies of A and a; explain why counting only AA would be wrong.
What are p(A)=0.45 and q(a)=0.55? A copies = 2(20)+50=90 of 200 total alleles; heterozygotes each contribute one A and one a.
100

The movement of alleles between populations through migration and interbreeding.

What is gene flow?

100

Selection that shifts a population's phenotypes toward one extreme, as when dark peppered moths became common near sooty industrial cities.

What is directional selection?

100

Speciation that occurs when a physical barrier, such as a mountain range or river, splits a population.

What is allopatric speciation?

100

Structures that share a common evolutionary origin even when their functions differ, like a bat wing and a human arm.

What are homologous structures?

200
At a locus, p(A)=0.70 in a large randomly mating population. For 1,000 zygotes, predict the number of heterozygotes and state the key assumption needed for 2pq.
What is 420 Aa zygotes? 2pq=2(0.70)(0.30)=0.42; random mating is needed for Hardy-Weinberg genotype proportions.
200

When a small group of colonists starts a new population, its allele frequencies can differ from the source population; this is called this effect.

What is the founder effect?

200

Selection that favors intermediate phenotypes and removes both extremes, as with human birth weight.

What is stabilizing selection?

200

Speciation without geographic separation, often through polyploidy in plants.

What is sympatric speciation?

200

Structures with similar functions but separate evolutionary origins, like bird wings and insect wings, result from this process.

What are analogous structures (convergent evolution)?

300
At p(A)=0.60, Hardy-Weinberg predicts 2pq=0.48 heterozygotes, but only 0.24 are observed. Name one plausible cause and explain why this deficit alone does not prove selection.
What is nonrandom mating such as inbreeding, or population subdivision? These can raise homozygosity without necessarily changing allele frequencies; a heterozygote deficit alone does not establish fitness differences.
300

A sudden, drastic reduction in population size that sharply cuts genetic variation, as seen in cheetahs and northern elephant seals.

What is a population bottleneck?

300

Selection that favors both extreme phenotypes over the intermediate, as in birds with very large or very small beaks and few medium ones.

What is disruptive selection?

300

This prezygotic barrier keeps species apart because they breed at different times of day or year.

What is temporal isolation?

300

Reduced or nonfunctional remnants of structures that were useful in ancestors, such as the pelvic bones in whales.

What are vestigial structures?

400
A storm randomly leaves 10 of 10,000 beetles. The blue allele jumps from 0.20 to 0.60, with no measured color advantage. Name the process and why this observation does not establish natural selection.
What is a bottleneck causing genetic drift? Random survival samples a small gene pool, so chance can shift allele frequencies; a fitness advantage has not been shown.
400

The ultimate source of all new alleles, including point changes, insertions, deletions and duplications.

What is mutation?

400

When heterozygotes have higher fitness than either homozygote, both alleles are maintained, as with sickle-cell and malaria.

What is heterozygote advantage (a form of balancing selection)?

400

In this postzygotic barrier, hybrids such as mules survive to adulthood but are sterile.

What is reduced hybrid fertility (hybrid sterility)?

400

A group that includes a common ancestor and ALL of its descendants is described by this term, also called a clade.

What is a monophyletic group?

500

To stay in Hardy-Weinberg equilibrium, a population must meet five conditions; name any four of them.

What are no mutation, no gene flow, random mating, a very large population (no genetic drift), and no natural selection?

500

In this form of nonrandom mating, individuals mate with relatives, raising homozygosity without changing allele frequencies.

What is inbreeding?

500

In this selection, a phenotype's fitness depends on how common it is, as in scale-eating fish whose rarer mouth direction gains an edge.

What is negative frequency-dependent selection?

500

Rapid diversification of one ancestral lineage into many ecologically different species, as with Darwin's finches.

What is adaptive radiation?

500

A shared derived character that is present in a clade's members but absent from earlier ancestors is known by this term.

What is a synapomorphy?