Relate Variation to Selection Pressure - Biology

Identify the most likely selective force when bacteria are exposed to an antibiotic.

Antibiotic acts as a selection pressure favoring resistant cells. Antibiotics create directional selection for resistance.
Identify the most likely result if a drought reduces water availability for many years.

Selection favors traits that improve water conservation. Drought creates strong selection for water-saving adaptations.
Identify the selection pressure most directly increased by a new predator in the habitat.

Predation pressure. New predators create immediate survival challenges.
What is meant by "selection is environment-dependent"?

A trait can be beneficial in one environment and harmful in another. Fitness depends entirely on environmental context.
Identify the correct inference if only the fastest prey survive predator attacks.

Selection favors alleles that increase speed. Speed becomes directly linked to survival and reproduction.
What is artificial selection?

Human-directed breeding that changes trait frequencies. Humans act as the selective agent in breeding programs.
Which outcome best indicates an adaptation rather than an acclimation?

A heritable trait becomes more common across generations. Adaptation involves genetic change across generations.
What is the role of mutations in natural selection?

They create new alleles that can be acted on by selection. Without mutations, there would be no variation to select from.
What is directional selection?

Selection that favors one extreme phenotype. The population mean shifts toward the favored extreme.
What is the difference between genotype and phenotype?

Genotype is genetic makeup; phenotype is expressed traits. Selection acts on phenotype but changes genotype frequencies.
Identify the correct interpretation if a new disease increases mortality in one genotype.

The disease is a selection pressure against that genotype. Disease creates differential survival based on genotype.
Which statement best predicts allele frequency change if a phenotype has higher fitness?

Alleles contributing to that phenotype tend to increase over generations. Higher fitness genotypes become more common over time.
What is gene pool in population genetics?

All alleles present in a population. The total genetic diversity available for selection.
What is the main requirement for natural selection to occur?

Heritable variation that affects fitness. Without heritable variation affecting fitness, no evolution occurs.
Identify the correct statement about mutations and selection.

Mutations arise randomly; selection is nonrandom. Mutation provides variation; selection filters it non-randomly.
What is an example of a biotic selection pressure?

Predation (an interaction with other organisms). Biological interactions create complex selection pressures.
What is the correct relationship between selection and variation?

Selection filters existing heritable variation; it does not create it. Selection sorts existing variation; it doesn't generate novelty.
What is a selection pressure in natural selection?

An environmental factor that affects survival or reproduction. These pressures determine which traits are advantageous.
Identify the best conclusion if two phenotypes have equal fitness in an environment.

Selection does not favor either phenotype (no directional change). Equal fitness means no selective advantage for either form.
What is meant by "trade-off" in adaptations?

A trait increases fitness in one way but decreases it in another. Evolution often involves compromises between competing needs.
Which trait is most likely favored when food becomes scarce and hard to access?

Traits that improve foraging efficiency or resource use. Food scarcity selects for improved resource acquisition.
What is the role of recombination in variation?

It reshuffles alleles, creating new genotype combinations. Sexual reproduction increases genetic diversity in offspring.
What does it mean that selection acts on phenotypes?

Environment filters expressed traits, not alleles directly. Selection cannot directly see genes, only their expression.
Which statement best distinguishes natural selection from evolution?

Selection is a mechanism; evolution is allele frequency change. Selection is the cause; evolution is the measured outcome.
Which scenario best illustrates sexual selection rather than natural selection for survival?

A trait increases mating success despite survival costs. Sexual selection can oppose survival-based natural selection.
Which type of selection is occurring if the population mean shifts toward larger size?

Directional selection. Population mean shifts toward the favored direction.
What is the selective advantage of camouflage in many habitats?

Reduced detection by predators or prey. Camouflage increases survival by avoiding detection.
Which outcome best indicates that a trait is heritable rather than purely environmental?

Offspring resemble parents for the trait across environments. Heritability shows genetic rather than environmental control.
What does it mean that evolution is measured in populations?

Allele frequencies change across generations in a population. Individuals don't evolve; population gene pools change.
What is an example of an abiotic selection pressure?

Temperature (a nonliving environmental factor). Physical environment creates selection without other organisms.
Which option best explains why selection cannot produce a needed trait on demand?

Selection acts only on existing heritable variation. Selection cannot create variation; it only filters what exists.
What is disruptive selection?

Selection that favors both extreme phenotypes over intermediates. Can lead to population splitting into two distinct forms.
What is genetic variation in a population?

Heritable differences in DNA/alleles among individuals. This forms the raw material for natural selection to act upon.
Which type of selection is occurring if intermediates are selected against and extremes increase?

Disruptive selection. Both extremes are favored over intermediate forms.
Which option best defines "selective agent"?

The specific factor (for example, predator) causing selection. The specific environmental force driving selection.
What is fitness in evolutionary biology?

Relative reproductive success of an individual or genotype. Higher fitness means more offspring in the next generation.
What is pesticide resistance an example of?

Natural selection favoring resistant pests. Pesticides act as environmental selection pressures.
What is adaptation?

A heritable trait that increases fitness in a given environment. Adaptations evolve through natural selection over time.
Which type of selection is occurring if extremes are removed and variation decreases?

Stabilizing selection. Intermediate phenotypes are favored over extremes.
What is meant by differential reproductive success?

Some individuals leave more offspring than others. Fitness differences drive changes in allele frequencies.
What is stabilizing selection?

Selection that favors intermediate phenotypes. Reduces variation by eliminating extreme phenotypes.
Identify the most likely effect of a selective pressure that targets juveniles only.

Traits improving juvenile survival increase in frequency. Early survival strongly impacts lifetime reproductive success.
Identify the outcome of strong selection against a harmful phenotype.

That phenotype becomes less common over generations. Strong selection reduces frequency of disadvantageous traits.
What is natural selection?

Differential survival and reproduction of heritable variants. This process drives evolutionary change in populations.
What is heritability in the context of selection?

The degree to which trait differences are genetic and inherited. Only heritable traits can respond to natural selection.
Identify the correct conclusion if a trait increases survival but reduces mating success.

Overall fitness may decrease if reproduction drops enough. Fitness depends on both survival and reproductive components.
Which statement best describes selection when the environment changes rapidly?

Previously beneficial traits may become neutral or harmful. Environmental change can reverse previous selective advantages.
Which condition must be true for selection to change allele frequencies?

Trait variation must be heritable and affect fitness. Both conditions are necessary for evolutionary change.
What is antibiotic resistance an example of?

Natural selection favoring resistant bacterial variants. Antibiotics create strong directional selection pressure.

Study these flashcards