Biology 152: Unit 1

What is evolution?

Descent with modification; a change in the genetic composition of a population over time.

How is the genetic composition of a population measured?

By the frequencies of alleles in the population.

What is the unit of evolution?

The population.

What types of evidence show evolutionary change?

Anatomy, fossils, embryos, genomes, and species distributions.

What did Aristotle believe about species?

Species were fixed, permanent, and arranged on a scala naturae.

What is a scala naturae?

A fixed hierarchical arrangement of life forms.

What was William Paley’s Natural Theology argument?

Complex natural structures imply a designer, like a watch implies a watchmaker.

What major contribution did Carolus Linnaeus make?

He established the binomial classification system.

How did Linnaeus view species?

He viewed Earth and species as immutable.

What is uniformitarianism?

Earth changes through continuous, gradually acting processes.

Who proposed uniformitarianism?

James Hutton.

What does uniformitarianism suggest about natural laws?

Natural laws acting today also acted in the past.

What is geological deep time?

The idea that Earth has existed long enough for slow geological processes to cause major change.

What was Thomas Malthus’s key idea about populations?

Populations grow faster than available resources.

What happens when population growth exceeds available resources?

Resources become limiting and restrict population growth.

Who is considered the founder of paleontology?

Georges Cuvier.

What did Cuvier observe about fossils?

Fossils become more different from modern organisms deeper in the fossil record.

What major idea did Cuvier’s work support?

Extinction is a widespread process.

Who are the two scientists associated with natural selection?

Charles Darwin and Alfred Russel Wallace.

Who was Jean-Baptiste Lamarck?

A pre-Darwinian scientist who proposed an early hypothesis of evolutionary transformation.

What is Lamarck’s idea of inheritance of acquired characteristics?

Changes an organism acquires during life are passed to its offspring.

What is Lamarck’s idea of use and disuse?

Used traits become more developed, while unused traits weaken or disappear.

Did Lamarck believe in common ancestry?

No. He believed species arose separately and progressed along similar paths.

Why was Lamarck’s evolutionary explanation rejected?

Evidence did not support inheritance of acquired traits or his model of species change.

What important observation did Darwin make about species distributions?

Closely related species tend to occur near each other geographically.

What is diversity?

The number of different species.

What is variation?

Differences in traits among individuals of the same species.

What is endemism?

The condition of being found in one location and nowhere else.

What is an adaptation?

A trait that makes an organism well suited to its environment.

What was Darwin’s major insight about the relationships among species?

Different species can descend from common ancestors.

What is common ancestry?

The idea that different species descend from shared ancestral species.

What happens to traits during divergence from a common ancestor?

Descendant lineages accumulate different trait changes over time.

What does common ancestry help explain?

Classification patterns, biogeography, and transitional fossils.

Why does common ancestry require evolution?

Descendants differ from ancestors, so their traits must change over time.

What is biogeography?

The study of the geographic distribution of organisms.

What major contribution did Alfred Russel Wallace make?

He independently developed ideas about evolution and helped found biogeography.

What was Wallace’s Sarawak Law?

Closely related species tend to arise near one another in space and time.

What happened when Wallace contacted Darwin in 1858?

Wallace sent Darwin a theory of evolution that was very similar to Darwin’s own.

What is the first requirement for natural selection?

Variation in traits within a natural population.

What is differential survival and reproduction?

Some individuals survive and reproduce more successfully than others.

Why does overproduction of offspring matter for natural selection?

More offspring are produced than the environment can support, creating competition.

What role does heredity play in natural selection?

Traits that improve survival or reproduction must be inheritable.

What happens when individuals with favorable inherited traits reproduce more?

Those traits become more common over generations.

What is the result of natural selection over time?

Favorable traits, or adaptations, accumulate in the population.

Does natural selection act directly on individuals or populations?

Selection acts on individuals, while evolutionary change occurs across the population.

What determines an individual’s success under natural selection?

Surviving to reproduce and leaving offspring that carry its alleles.

What is a population?

A group of organisms connected by gene flow, usually through mating and reproduction.

What two major problems did Darwin’s theory initially face?

No direct observations of wild populations evolving and no known mechanism of heredity.

Whose work eventually explained a mechanism of heredity?

Gregor Mendel’s.

What is artificial selection?

Human-directed breeding of organisms for desired traits.

Why did Darwin use artificial selection as an analogy?

It showed that selection can cause substantial trait changes across generations.

What are the two major elements of modern evolutionary theory?

Common ancestry and natural selection.

How are common ancestry and natural selection connected?

Common ancestry explains shared descent; natural selection explains adaptive change.

What is the overall result of common ancestry plus natural selection?

Descent with modification.

What is genetics?

The study of heredity.

What is Mendel’s law of segregation?

The two alleles for a gene separate during gamete formation.

What is Mendel’s law of independent assortment?

Alleles of different genes assort independently during gamete formation.

What is the biological species concept?

A species is a set of populations that can interbreed and produce viable, fertile offspring.

What is speciation?

The splitting of one evolutionary lineage into separate species.

What is a phylogeny?

A representation of evolutionary relationships among species.

What is population genetics?

The study of allele-frequency distributions and changes within and among populations.

What five forces can cause evolutionary change in populations?

Natural selection, genetic drift, mutation, migration, and non-random mating.

What is a gene pool?

All copies of all alleles at all loci in a population.

How do you calculate the total number of alleles at one locus in a diploid population?

Number of individuals × 2.

How do homozygous individuals contribute to an allele count?

Each homozygous individual contributes two copies of that allele.

How do heterozygous individuals contribute to an allele count?

Each heterozygote contributes one copy of each allele.

How do you calculate an allele frequency from genotype counts?

Number of copies of the allele ÷ total number of alleles.

What do p and q represent in Hardy-Weinberg equations?

The frequencies of the two alleles in a population.

What equation describes allele frequencies for a two-allele locus?

p + q = 1.

Under Hardy-Weinberg equilibrium, what is the frequency of A₁A₁?

p².

Under Hardy-Weinberg equilibrium, what is the frequency of A₁A₂?

2pq.

Under Hardy-Weinberg equilibrium, what is the frequency of A₂A₂?

q².

What is the Hardy-Weinberg genotype-frequency equation?

p² + 2pq + q² = 1.

What does Hardy-Weinberg equilibrium represent?

A population whose genotype frequencies are consistent with no evolutionary change.

Why is Hardy-Weinberg equilibrium called a null model?

It provides an expected “no evolution” pattern to compare with real populations.

What five assumptions are required for Hardy-Weinberg equilibrium?

No mutation, no migration, no selection, random mating, and a very large population.

Why does mutation violate Hardy-Weinberg assumptions?

Mutation can create new alleles and change allele frequencies.

Why does migration violate Hardy-Weinberg assumptions?

Migration can introduce or remove alleles and change allele frequencies.

Why does selection violate Hardy-Weinberg assumptions?

Different genotypes can leave different numbers of offspring, changing allele frequencies.

Why does non-random mating violate Hardy-Weinberg assumptions?

Mating patterns can alter the expected genotype frequencies.

Why must a Hardy-Weinberg population be very large?

Small populations experience stronger random changes in allele frequencies.

If p = 0.2 and q = 0.8, what are the expected genotype frequencies?

p² = 0.04, 2pq = 0.32, q² = 0.64.

How can you find an allele frequency if given a homozygous genotype frequency?

Take the square root of the homozygous genotype frequency.

If p² = 0.09, what is p?

0.30.

Once you know one allele frequency, how do you find the other?

Subtract it from 1.

If p = 0.30, what is q?

0.70.

Does having constant allele frequencies automatically mean a population is in Hardy-Weinberg equilibrium?

No. Its genotype frequencies must also match p², 2pq, and q².

How is Hardy-Weinberg equilibrium used with real data?

Compare observed genotype frequencies with expected frequencies to test for evolution.

What is genetic drift?

Random changes in allele frequencies from one generation to the next.

What causes genetic drift?

Chance sampling of alleles during reproduction.

Is genetic drift random or adaptive?

Random.

In what populations is genetic drift strongest?

Small populations.

Why is genetic drift stronger in small populations?

Random sampling has a larger effect when fewer individuals contribute alleles.

What effect does genetic drift have on genetic variation?

It tends to remove variation from a population.

What does it mean when an allele becomes fixed?

Its frequency reaches 1.0.

What does it mean when an allele is lost?

Its frequency reaches 0.

Can an allele lost through drift naturally reappear in the same population?

Only through processes such as a new mutation.

What happens to allele frequencies during genetic drift?

They undergo a random walk and may eventually reach fixation or loss.

Why can evolution occur even without natural selection?

Genetic drift can change allele frequencies purely by chance.

What is a population bottleneck?

A drastic reduction in population size that causes intense genetic drift.