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Questions on natural selection, evidence for evolution, genetic drift, modes of selection and speciation. Written for AP Biology and intro college biology.
Which condition is required for natural selection to change a population?
Individuals changing their traits during their lifetime to suit the environment
Heritable variation in traits that affect survival or reproduction
A population in which all individuals are genetically identical
Organisms trying to adapt to their surroundings
Selection acts on existing variation that can be passed to offspring. Traits acquired during a lifetime (Lamarck's idea) are not inherited, and organisms do not adapt on purpose.
The human arm, a bat's wing and a whale's flipper have the same basic bone arrangement. These are:
Analogous structures
Vestigial structures
Homologous structures
The result of convergent evolution
Homologous structures share an underlying plan because they come from a common ancestor, even if they now have different functions. Analogous structures look or work alike but evolved independently.
Bird wings and insect wings both allow flight but evolved independently. They are an example of:
Analogous structures produced by convergent evolution
Homologous structures inherited from a common ancestor
Vestigial structures
Divergent evolution
Similar selective pressures (flying) produced similar functions in unrelated lineages. The internal structure is completely different, so they are not homologous.
A storm kills 90% of a beetle population at random, regardless of their traits. The resulting change in allele frequencies is an example of:
The bottleneck effect (genetic drift)
Natural selection
Gene flow
Sexual selection
Survival here had nothing to do with traits, so it is chance (drift), not selection. A bottleneck is a sharp drop in population size; the founder effect is the related case where a few individuals start a new population.
A few birds colonize a remote island and happen to carry a rare allele at high frequency. Generations later the allele is still common there. This is:
Directional selection
Gene flow
The founder effect
Hardy-Weinberg equilibrium
The new population's gene pool reflects the small, random sample of founders. It is a form of genetic drift, which has the biggest effect in small populations.
After a drought leaves only large, hard seeds, the average beak depth of a finch population increases over generations. This is:
Stabilizing selection
Disruptive selection
Artificial selection
Directional selection
One extreme (deep beaks) is favored, so the mean shifts in that direction. This is the Grants' famous observation of Galápagos finches.
Human birth weights cluster around an intermediate value because very small and very large babies historically had lower survival. This is:
Directional selection
Disruptive selection
Stabilizing selection
Genetic drift
Stabilizing selection favors the middle and removes both extremes, which narrows variation without moving the mean. Disruptive selection would favor both extremes over the middle.
Two frog populations live in the same pond but breed in different months, so they no longer interbreed. This barrier is:
Habitat isolation
Temporal isolation
Hybrid sterility
Mechanical isolation
Breeding at different times is temporal isolation, a prezygotic barrier. Hybrid sterility is postzygotic: hybrids form but cannot reproduce (like mules).
Speciation that follows the splitting of a population by a geographic barrier, such as a new river or mountain range, is called:
Allopatric speciation
Sympatric speciation
Artificial selection
Adaptive radiation
Allopatric means other homeland: the barrier stops gene flow, and the populations diverge. Sympatric speciation happens without geographic separation, for example through polyploidy in plants.
In evolutionary biology, fitness refers to:
Physical strength and endurance
How long an individual lives
Body size relative to others
An individual's reproductive success compared with others in the population
Fitness is measured in offspring that survive to reproduce. A strong, long-lived individual that leaves no offspring has zero fitness.
Why do bacterial populations become resistant to an antibiotic?
The antibiotic causes each bacterium to develop the resistance it needs
Bacteria learn to avoid the antibiotic
Bacteria that already carry resistance mutations survive and reproduce
The antibiotic gets weaker over time
Resistance mutations arise randomly, and some exist before the drug is used. The antibiotic kills the susceptible cells, so resistant ones take over. The drug selects; it does not cause the mutation.
On a phylogenetic tree, two species that share a more recent common ancestor are:
Always drawn next to each other at the tips
Descended directly from one another
Identical in body structure
More closely related to each other than to species that branched off earlier
Relatedness is read from branch points (nodes), not from how close the tips sit on the page, because branches can rotate. Living species on a tree are cousins, not ancestors of each other.
Carbon-14 has a half-life of about 5,730 years. A sample has 25% of its original carbon-14. About how old is it?
11,460 years
5,730 years
17,190 years
22,920 years
100% → 50% → 25% is two half-lives: 2 × 5,730 = 11,460 years. One half-life would leave 50%, three would leave 12.5%.
Which is an example of a vestigial structure?
The wings of a bat
The opposable thumb of humans
The pelvic bones of whales
The sharp eyes of an eagle
Whales have small pelvic bones that no longer support legs, a leftover of their four-legged land ancestors. The other options are structures that still have a clear current function.
The model in which species stay mostly unchanged for long periods, interrupted by short bursts of rapid change, is called:
Gradualism
Punctuated equilibrium
Uniformitarianism
Inheritance of acquired characteristics
Punctuated equilibrium (Eldredge and Gould) explains the sudden appearance of new forms in the fossil record. Gradualism proposes slow, steady change over long periods.
