What is evolution in the context of population genetics?	A change in allele frequencies in a population over successive generations.
According to Darwin's theory of natural selection, what does competition for limited resources lead to?	Differential survival: individuals with more favorable phenotypes are more likely to survive and produce more offspring, passing those traits on.
What is differential reproductive success?	The phenomenon where individuals with traits better suited to the environment survive and produce more viable offspring.
How is evolutionary fitness measured?	By reproductive success: an organism's contribution of offspring, and so of its alleles, to the next generation.
_____ acts directly on an individual's phenotype, but it is populations that evolve over time.	Natural selection
Natural selection acts directly on an individual's phenotype, but it is _____ that evolve over time.	populations
Does natural selection act directly on genotypes or on phenotypes?	On phenotypes: it acts on phenotypic variation in a population. Allele frequencies change as a result.
What is an adaptation in evolutionary biology?	A heritable trait that enhances an organism's ability to survive and reproduce in a specific environment.
Can the same allele help in one environment and hurt in another? Why?	Yes. Selective pressures differ between environments, so an allele that is adaptive in one can be harmful in another.
What is directional selection?	Natural selection that favors individuals at one extreme phenotypic range over others.
What is stabilizing selection?	Natural selection that favors intermediate variants by acting against extreme phenotypes.
What is disruptive selection?	Natural selection that favors individuals at both phenotypic extremes over intermediate phenotypes.
What is artificial selection?	The selective breeding of domesticated plants and animals by humans to encourage desirable phenotypic traits.
Which random process adds new genetic variation to a population?	Mutation. It supplies the variation that natural selection acts on.
What is genetic drift?	A change in the allele frequencies of a population due to chance events.
In what size population does genetic drift have the strongest effect?	Small populations.
What is the bottleneck effect?	A type of genetic drift that happens when a population is cut to a small number of individuals for at least one generation (for example, by a natural disaster).
What is the founder effect?	A type of genetic drift that happens when a few individuals are separated from the rest of the population; allele frequencies in the new population follow the founders' genes.
Why can genetic drift make a small population diverge from other populations of its species?	Chance changes in allele frequency are biggest in small populations, so its allele frequencies can drift away from the others'.
What is gene flow?	The transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes.
What does gene flow between two populations do to their chance of becoming separate species?	It lowers it: gene flow keeps the populations from diverging into separate species.
What is the evidence that a population is evolving?	A change in its allele frequencies over time.
In the Hardy–Weinberg equation p + q = 1, what does p represent?	The frequency of one of the two alleles (by convention, the dominant allele).
In the Hardy–Weinberg equation p + q = 1, what does q represent?	The frequency of the other allele (by convention, the recessive allele).
In the Hardy–Weinberg equation p² + 2pq + q² = 1, which term represents the frequency of heterozygous individuals?	2pq
In the Hardy–Weinberg equation p² + 2pq + q² = 1, which term represents the frequency of homozygous dominant individuals?	p²
In the Hardy–Weinberg equation p² + 2pq + q² = 1, which term represents the frequency of homozygous recessive individuals?	q²
Name the five conditions required for a population to maintain Hardy–Weinberg equilibrium.	No mutations, random mating, no natural selection, extremely large population size, and no gene flow.
The Hardy–Weinberg conditions are never met in nature. Why is the model still useful?	It is a null hypothesis: if allele frequencies change, at least one condition is being violated, so the population is evolving.
If allele frequencies in a population change from one generation to the next, the population is violating _____ and undergoing evolution.	Hardy–Weinberg equilibrium
If allele frequencies in a population change from one generation to the next, the population is violating Hardy–Weinberg equilibrium and undergoing _____.	evolution
A population is in Hardy–Weinberg equilibrium and 16% of individuals show the recessive phenotype. What are q and p?	q² = 0.16, so q = 0.4 and p = 1 − 0.4 = 0.6.
In that population (q = 0.4, p = 0.6), what fraction of individuals is heterozygous?	2pq = 2 × 0.6 × 0.4 = 0.48, or 48%.
If 9% of a population shows the recessive phenotype, why is q not 0.09?	0.09 is q², a genotype frequency. The allele frequency is q = √0.09 = 0.3.
Name the 3 ways fossils can be dated in AP Biology.	The age of the rocks the fossil is found in, the rate of decay of isotopes such as carbon-14, and geographical data.
What are homologous structures?	Anatomical features that share a common evolutionary origin despite differences in current function.
What are analogous structures?	Features that perform similar functions but evolved independently due to convergent evolution, not shared ancestry.
What is convergent evolution?	The independent evolution of similar features in distinct evolutionary lineages due to similar selective pressures.
What is a vestigial structure?	A remnant feature that served an important function in an organism's ancestors but has reduced or no function today.
Which usually gives more accurate and reliable evidence for evolutionary relationships: molecular data or morphological traits?	Molecular data: comparisons of DNA nucleotide sequences and protein amino acid sequences.
Name the 3 pieces of evidence that all eukaryotes share a common ancestor.	Membrane-bound organelles, linear chromosomes, and genes that contain introns.
Give 2 examples showing that evolution is still happening.	Resistance to antibiotics, pesticides, herbicides or chemotherapy drugs, and pathogens evolving to cause emergent diseases.
Why does using an antibiotic make resistant bacteria more common?	Bacteria that already carry resistance survive and reproduce while susceptible ones die, so the resistance allele's frequency rises.
What is a phylogenetic tree?	A diagram that represents a hypothesis about the evolutionary history and relationships of a group of organisms.
What does a phylogenetic tree show that a cladogram does not?	The amount of change over time, calibrated by fossils or a molecular clock. A cladogram shows relationships, not a time scale.
Are phylogenetic trees and cladograms facts or hypotheses?	Hypotheses: they can be tested and are revised as new evidence comes in.
On a phylogenetic tree, what does a branch point (node) represent?	The most recent common ancestor of the evolutionary lineages that diverge from that point.
On a cladogram, the _____ is the lineage least closely related to all the other organisms shown.	outgroup
What is a sister taxon?	One of two lineages that stem from the same branch point; the pair shares an immediate common ancestor that no other group shares.
What is a monophyletic group (clade)?	A group composed of an ancestral species and all of its descendants.
What is a shared derived character?	A trait that evolved in a common ancestor and is shared by its descendants but not by earlier lineages, such as hair in humans and rabbits but not lizards. It marks common ancestry.
What does the principle of maximum parsimony state when constructing a phylogenetic tree?	The tree that needs the fewest evolutionary changes to explain the evidence is the most likely one.
According to the biological species concept, what defines a species?	A group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring.
When does speciation occur?	When two populations become reproductively isolated from each other.
What is allopatric speciation?	Speciation that occurs when populations are geographically separated from one another.
What is sympatric speciation?	Speciation that occurs in populations that live in the same geographic area.
What is a prezygotic reproductive barrier?	An isolating mechanism that prevents mating or fertilization between different species.
What is temporal isolation?	A prezygotic barrier in which species breed during different seasons, times of day, or years.
What is behavioral isolation?	A prezygotic barrier in which specific courtship rituals or behaviors prevent interbreeding.
What is mechanical isolation?	A prezygotic barrier where morphological differences prevent successful copulation.
What is gametic isolation?	A prezygotic barrier where sperm of one species cannot fertilize the eggs of another species.
What is a postzygotic reproductive barrier?	A mechanism that prevents hybrid zygotes from developing into viable, fertile adults.
What is hybrid sterility?	A postzygotic barrier where the hybrid offspring develops into a viable adult but cannot produce functional gametes.
What is punctuated equilibrium?	A model in which evolution happens rapidly after a long period of stasis.
What is gradualism in the context of evolutionary tempo?	A model in which evolution happens slowly, through small changes over hundreds of thousands or millions of years.
What is divergent evolution?	Adaptation to new habitats that leads related populations to become phenotypically different.
_____ is the rapid evolution of many diversely adapted species from a common ancestor upon introduction to novel environmental niches.	Adaptive radiation
Why are populations with little genetic diversity at greater risk of decline or extinction?	They are less likely to contain individuals that can withstand a new environmental pressure, such as a disease outbreak.
About how old is Earth?	About 4.6 billion years old.
When did Earth become hospitable to life, and how old is the earliest fossil evidence of life?	It was too hostile for life until about 3.9 billion years ago; the earliest fossils date to about 3.5 billion years ago.
What does the RNA world hypothesis propose?	That RNA could have been the earliest genetic material, copied by base-pairing before genetically encoded proteins acted as catalysts.