Week 7: Natural Selection & Evolution Flashcards

How does antibiotic resistance develop through natural selection?

Random mutations create resistant bacteria; antibiotics kill non-resistant ones, so resistant individuals survive and reproduce, increasing resistance alleles in the population.

What is the ultimate source of new variation?

Mutation — random changes in DNA that create new alleles.

Does a change in the environment cause new traits to appear?

No — environmental change only selects existing traits; it does not create new ones.

What is an allele?

A version of a gene (e.g., eye color alleles, shell color alleles, AVPR1a variants).

Define evolution in under 10 words.

Change in allele frequencies in a population’s gene pool over time.

How does unequal reproductive success cause evolution?

Individuals with beneficial traits leave more offspring, increasing those alleles in the gene pool.

Can individuals evolve?

No — only populations evolve; individual genes do not change during life.

Does environmental change cause variation to appear?

No — variation must already exist; if not, the population may go extinct.

What does the “selecting” in natural selection?

The environment — it favors traits that improve survival and reproduction.

Why are adaptations often compromises?

Traits balance competing needs; e.g., racehorse (speed but fragile) vs mustang (stronger but slower).

What happens if variation is insufficient for survival during rapid change?

The species may go extinct — seen as sudden loss of diversity in the fossil record.

Define population.

A group of individuals of the same species in one area.

Define gene pool.

The total collection of alleles in a population.

Define gene flow.

The movement of alleles between populations through migration or mating.

Define evolution.

A change in allele frequencies in a population over time.

Define microevolution.

Small-scale evolutionary changes within a population or species.

What is fitness in evolutionary terms?

The number of surviving offspring an individual produces — not strength or lifespan.

What are the three main causes of evolutionary change?

Natural selection, genetic drift, and gene flow.

What are the three types of natural selection?

Directional: one extreme favored; Stabilizing: middle favored; Disruptive: both extremes favored.

What is a species (biological species concept)?

A group of organisms that can interbreed and produce fertile offspring.

When is the biological species concept not useful?

For asexual organisms, fossils, or species that don’t reproduce sexually.

What is speciation?

The formation of a new species from existing ones.

What is a reproductive barrier?

A factor that prevents interbreeding between populations.

Give examples of prezygotic barriers.

Behavioral differences, mating times, or incompatible reproductive structures.

Give examples of postzygotic barriers.

Sterile or inviable hybrids (e.g., mule from horse × donkey).

What is allopatric speciation?

Speciation caused by geographic separation (e.g., salamanders in California).

What is sympatric speciation?

where new species evolve from a single ancestral species while inhabiting the same geographic area, without any physical separation

What is genetic drift?

Random elimination/change in alleles gene pool, especially in small populations.

What is gene flow?

Movement of alleles between populations; increases genetic diversity.

Which increases genetic diversity — genetic drift or gene flow?

Gene flow increases; genetic drift decreases diversity.

Why are drift and flow called “nonadaptive”?

They happen by chance, not due to survival advantage.

What is Hardy–Weinberg Equilibrium?

A population where allele frequencies remain constant — no evolution.

What are the five Hardy–Weinberg conditions for no evolution?

1. No mutations; 2. No gene flow; 3. Random mating; 4. Large population size; 5. No natural selection.

Why is Hardy–Weinberg useful?

It provides a baseline to measure whether evolution is occurring.