BIO150 Exam 4 Study Guide

Approximately how many species have been described on Earth?

1.4 million

What does evolution explain (two main things)?

• The diversity of organisms

• Their adaptations and patterns

of distribution and abundance

What is the definition of evolution (three words)

descent with modification

What was Darwin’s major contribution to our understanding of evolution?

Both a Pattern and a Process

1) Organisms are related

by descent from

common ancestors

2) Organisms have

changed over time

Natural Selection

What three criteria must a scientific explanation fulfill?

1) Be based on evidence from

natural processes that can be

observed and replicated

2) Produce findings or hypotheses that

can be confirmed empirically

(tested & falsified)

3) Be open to debate and change

How does convergent evolution provide support for evolution?

Organisms adapting to similar environments should evolve similar morphologies

Describe an example of how evolution is useful in medicine? Conservation? Agriculture?

Antibiotic resistance, pesticide resistance, adaptation

What evidence do we have for the pattern of evolution?

Species are related because of common descent and species changed over time

Biogeography

Distribution of species

Homology

similarities due to sharing a common ancestor
The forelimbs of vertebrates—including human arms, bat wings, whale flippers, and dog legs

What evidence do we have that species have changed through time?

Law of succession

Extinctions: Fossil and Recent

Vestigial traits

What are vestigial traits?

Historical Leftovers

Why are some species of cavefish blind? Describe how the experiments helped scientists

understand natural selection.

Natural selection favored fish that developed better metabolic efficiency, increased fat storage, and improved sensory abilities, instead of wasting energy

What does it mean for a trait to vary within and among populations?

Variation in traits occurs due to differences within a specific population and also among different populations.

What are the three conditions required for natural selection to operate?

1 ) Individuals within a population vary in their

characteristics (traits).

2) The variable traits are heritable.

3) These traits help individuals survive better or

reproduce more

Why must genetic variation be present for a trait to evolve?

Genetic variation is essential for natural selection to act upon, allowing traits to adapt or evolve over time.

Why was there a rapid shift in bill size in the medium ground finch following a severe drought?

drought reduced small seed availability, making large, tough seeds the primary food source.

After the drought ended, why didn’t mean bill size rapidly shift back to the mean just before the

drought

Natural selection can’t reverse

If bill size was not heritable, would there have been a change in bill size in response to the

drought?

There would be no evolutionary change

does artificial selection usually proceed more rapidly than natural selection?

humans apply direct, consistent breeding pressure to select for specific traits

If natural selection operates on individuals, why does evolutionary change occur at the population level?

Evolutionary change occurs at the population level because natural selection affects traits within individuals that contribute to the population's genetic makeup.

What are four evolutionary mechanisms that change allele frequencies within populations?

Which of these mechanisms involves differential survival and reproductive success?

Natural selection

Mutation

Migration (= gene flow)

Genetic drift

How do we test for evolution?

Using the Hardy-Weinberg Model to predict allele and genotype frequencies under conditions without evolution

What are the assumptions of the Hardy-Weinberg Theorem (model)?

1) Large population size 2) No mutation 3) No migration 4) Random mating 5) No natural selection

If the Hardy-Weinberg assumptions are met, then after a generation of random mating, what will happen to genotype frequencies?

genotype frequencies will stabilize

What is the Hardy-Weinberg formula?

p2 + 2pq + q2

Define genetic drift and explain why it is especially prevalent in small populations?

This is any change in the allele frequencies in a population that is due to random chance

Less Genetic Variation and higher impact

What is a population bottleneck? Give examples of population bottlenecks that reduced genetic diversity.

when a population experiences a severe reduction in size: Greater Prairie-chickens

What is the cause (mechanism) of inbreeding depression?

increased homozygosity of recessive deleterious alleles

What are the four types of natural selection? Give an example of each.

Directional selection, Stabilizing selection, Disruptive selection, Balancing selection

Directional

Favors one extreme (or the other)

Stabilizing

favors intermediate individuals

Disruptive

favors different genotypes that produce different phenotypes

Balancing

maintains genetic variation

How does each form of natural selection influence the mean phenotype? How does each form of selection influence the variance of the phenotype?

three main forms of natural selection influence the mean and variance of a phenotype

Which form of natural selection is least common in the wild?

Disruptive selection

What are two common mechanisms generating balancing selection?

Heterozygote Advantage, Negative frequency-dependent selection

Heterozygote Advantage

fewer parasites

Negative frequency-dependent selection

Males with the F10 allele have fewer parasites

What is sexual selection?

Occurs when individuals differ in their ability to attract mates, non-random mating

Why are sexually selected traits usually more exaggerated in males than in females?

much higher variance in reproductive success than females, leading to intense competition for mates.
Eggs are expensive, sperm are cheap

What is extra-pair mating and how does it impact the variance in reproductive success in a population?

sexual interactions between monogamous individuals outside their established pair bond
successful males to dramatically increase their total reproductive success,

Speciation is the result of what two processes?

Isolation and Divergence

Explain what is meant by the Biological Species Concept.

Species: individuals that interbreed (or have the potential to interbreed) in natural environments. Individuals of different species cannot interbreed, and their populations are considered reproductively isolated

Describe the steps of allopatric speciation.

1) geographic isolation occurs
2) two populations must become isolated geographically from one another
3) the become separate species or interbreed

Explain how founder events can contribute to allopatric speciation

isolating a small group of individuals, which triggers rapid genetic changes—through genetic drift and intense natural selection

What is an adaptive radiation?

evolution of many species from a common ancestor
Adaptive radiation can be triggered by extinction, colonization events, and morphological innovations

What are premating isolating mechanisms? How do they differ from postmating isolating

mechanisms? How does each reduce the likelihood of interspecific mating?

Premating mechanisms stop interspecific mating through spatial, temporal, or behavioral differences, while postmating mechanisms stop gene flow after mating has occurred

How does sympatric speciation differ from allopatric speciation? Describe an example of

sympatric speciation.

Sympatric speciation occurs in populations that occupy the same geographic area. Over time, these two groups became genetically distinct and are now considered separate species

What are some limitations of the fossil record?

A nonrandom sample of the past:

1) Hard-bodied animals are much more likely to fossilize than soft-bodied animals.

2) Recent fossils are more common (more likely to be exposed)

3) Aquatic species more common (sediments cover them)

What was the Cambrian explosion? What morphological innovations arose during this period?

a relatively rapid evolutionary event where most major animal phyla ( Shells,

skeletons, claws, spines) first appeared in the fossil record

How can gene duplication lead to diversification?

leads to diversification by providing redundant genetic material that is free to mutate and evolve new functions without harming the organism

Describe the Permian-Triassic (P-T) extinction event.

Permian Extinctions associated with the formation of Pangea (marked end of Paleozoic)

Pangea is associated with less shoreline, drier continental interiors

90% of marine animals went extinct

50% of all species went extinct

Describe the Cretaceous-Tertiary (K-T) extinction event.

wiped out the dinosaurs and 60-80% of life at that time. Asteroid

Systematics

helps fill in the gaps in the fossil record by building phylogenetic trees of shared

derived traits