Unit 4 topic 2

What is microevolution?

A change in allele frequencies within a population across generations.

What is macroevolution?

Large-scale evolutionary change occurring over long periods of time, including the formation of new species and major evolutionary groups.

How are microevolution and macroevolution connected?

Macroevolutionary patterns arise from the accumulation of microevolutionary changes over many generations.

What is an allele frequency?

The proportion of a particular allele among all copies of that gene in a population's gene pool.

What is mutation?

A change in the DNA sequence that can create a new allele and introduce genetic variation into a population.

How does mutation contribute to microevolution?

Mutation creates new alleles, which can subsequently change in frequency through natural selection, genetic drift or gene flow.

Why is mutation important for evolution?

Mutation is the ultimate source of new genetic variation, providing new alleles for evolutionary processes to act upon.

What is gene flow?

The movement of alleles between populations when individuals or their gametes migrate and successfully reproduce.

How does gene flow change allele frequencies?

Immigration can introduce alleles into a population while emigration can remove alleles, changing the allele frequencies of populations.

How does gene flow affect genetic diversity?

Gene flow can increase genetic diversity within a population by introducing alleles from other populations.

What is genetic drift?

Random changes in allele frequencies caused by chance differences in which individuals survive and reproduce.

Why is genetic drift stronger in small populations?

Random events affect a larger proportion of individuals in small populations, causing greater changes in allele frequencies.

What is the founder effect?

A form of genetic drift that occurs when a small group establishes a new population with allele frequencies that differ from the original population.

What is a population bottleneck?

A form of genetic drift caused by a rapid reduction in population size, leaving a small and potentially unrepresentative sample of the original gene pool.

How does a population bottleneck reduce genetic diversity?

Alleles, particularly rare alleles, can be randomly lost when population size decreases, leaving fewer alleles in the surviving population.

What is natural selection?

The differential survival and reproduction of individuals caused by heritable variation interacting with environmental selection pressures.

What is required for natural selection to occur?

Heritable variation, differences in fitness and a selection pressure that causes individuals to have unequal reproductive success.

What is fitness?

An individual's relative ability to survive and reproduce successfully and contribute viable offspring to the next generation.

Does natural selection change individuals or populations?

Selection acts on individual phenotypes, but populations evolve because selection changes allele frequencies across generations.

What is stabilising selection?

Selection that favours intermediate phenotypes while selecting against both extreme phenotypes.

What is the effect of stabilising selection?

Intermediate phenotypes become more common while extreme phenotypes become less common, reducing phenotypic variation around the mean.

What is directional selection?

Selection that favours one extreme phenotype, causing the population's phenotypic distribution to shift towards that extreme.

What is disruptive selection?

Selection that favours both extreme phenotypes while selecting against intermediate phenotypes.

What is the effect of disruptive selection?

Extreme phenotypes become more common while intermediate phenotypes become less common, increasing phenotypic variation.

What is positive selection?

Selection that increases the frequency of an allele because individuals carrying it have greater fitness under the selection pressure.

What is negative selection?

Selection that decreases the frequency of an allele because individuals carrying it have lower fitness under the selection pressure.

Can a beneficial allele decrease in frequency?

Yes. Genetic drift, gene flow or other evolutionary forces can cause its frequency to decrease despite positive selection.

Can a harmful allele increase in frequency?

Yes. Genetic drift, gene flow or other evolutionary forces can cause its frequency to increase despite negative selection.

How can you identify positive selection from population data?

An allele consistently increasing in frequency across generations may indicate positive selection if other evolutionary forces are controlled.

How can you identify negative selection from population data?

An allele consistently decreasing in frequency across generations may indicate negative selection if other evolutionary forces are controlled.

What is the allele frequency formula?

Allele frequency = number of copies of the allele ÷ total number of alleles in the population.

How do you calculate the frequency of allele A?

p = [2(AA) + (Aa)] ÷ [2 × total number of individuals].

How do you calculate the frequency of allele a?

q = [2(aa) + (Aa)] ÷ [2 × total number of individuals].

What relationship must allele frequencies satisfy?

For a gene with two alleles, p + q = 1.

Why is each individual counted twice when calculating allele frequency?

Diploid organisms have two copies of each gene, so each individual contributes two alleles to the population's gene pool.

What is divergent evolution?

The process where related populations become increasingly different as they experience different environments or selection pressures.

What is an example of divergent evolution?

Finch populations from a common ancestor can evolve different beak characteristics when adapting to different food resources.

What is convergent evolution?

The independent evolution of similar traits in unrelated or distantly related organisms experiencing similar environmental selection pressures.

What is an example of convergent evolution?

Sharks and dolphins independently evolved streamlined bodies because both are adapted for efficient movement through water.

What is parallel evolution?

The independent evolution of similar traits in closely related lineages experiencing similar environmental conditions or selection pressures.

What is the difference between parallel and convergent evolution?

Parallel evolution generally occurs between more closely related lineages, whereas convergent evolution generally occurs between more distantly related lineages.

What is coevolution?

Reciprocal evolutionary change between interacting species where each species creates selection pressures that influence the evolution of the other.

What is an example of coevolution?

Predators and prey can drive reciprocal adaptations as each species evolves in response to selection pressures created by the other.

What is geographic isolation?

The physical separation of populations by barriers such as mountains, rivers or oceans, reducing or preventing gene flow.

What is temporal isolation?

Reproductive isolation caused by populations reproducing at different times, reducing or preventing gene flow between them.

What is spatial isolation?

Reduced gene flow caused by populations occupying different geographical locations or habitats.

What is reproductive isolation?

A condition where populations can no longer successfully interbreed to produce viable and fertile offspring.

What is speciation?

The formation of new species when populations become reproductively isolated and accumulate sufficient genetic differences.

What is allopatric speciation?

Speciation caused by geographic isolation, where a physical barrier separates populations and greatly reduces or prevents gene flow.

How does allopatric speciation occur?

Geographic isolation reduces gene flow, allowing populations to evolve independently until accumulated differences result in reproductive isolation.

What is sympatric speciation?

Speciation occurring without geographic separation when reproductive isolation develops between populations occupying the same geographical area.

How can sympatric speciation occur?

Differences in ecological niches, mate preferences, reproductive timing or chromosome number can reduce gene flow and lead to speciation.

What is parapatric speciation?

Speciation between neighbouring populations occupying different environments, with limited gene flow across an environmental boundary or gradient.

How does isolation affect gene flow?

Geographic, temporal and spatial isolation reduce gene flow, allowing populations to accumulate genetic differences independently.

How can reduced gene flow lead to speciation?

Reduced gene flow allows populations to accumulate different mutations and adaptations until sufficient genetic differences cause reproductive isolation.

What is genetic diversity?

The variety of different alleles present within a population or species.

Why is genetic diversity important?

It provides variation that allows populations to adapt to environmental change because different individuals may possess advantageous alleles.

Why does low genetic diversity increase extinction risk?

Low genetic diversity reduces adaptive potential and increases vulnerability to environmental change, disease and other selection pressures.

What is inbreeding?

Reproduction between genetically similar individuals that increases homozygosity and can increase the expression of harmful recessive alleles.

How can inbreeding increase extinction risk?

Inbreeding can increase harmful recessive alleles being expressed, reducing fitness and reproductive success in small populations.

What is comparative genomics?

The comparison of genome sequences between organisms to identify similarities, differences and evolutionary relationships.

How does comparative genomics provide evidence for evolution?

Similar DNA sequences between species indicate common ancestry, while differences reflect genetic divergence since their common ancestor.

What is a conserved sequence?

A DNA sequence that remains relatively similar between species because mutations in the sequence are often disadvantageous.

Why are some DNA sequences conserved?

Strong selection against harmful mutations in important DNA sequences causes those sequences to remain similar across evolutionary time.

How can conserved sequences be used to estimate divergence?

Closely related species generally have fewer differences in conserved sequences, allowing genetic differences to be used to estimate how long ago their lineages diverged.

What is a molecular clock?

A method for estimating the time since two species diverged by measuring genetic differences accumulated in their DNA.

What assumption does a molecular clock make?

It assumes genetic differences accumulate at a sufficiently predictable rate so sequence differences can estimate divergence time.

What is sequence divergence?

The accumulation of differences between DNA sequences in separate evolutionary lineages after they diverge from a common ancestor.

What is a cladogram?

A branching diagram showing hypothesised evolutionary relationships based on shared derived characteristics.

What does a branch point represent on a cladogram?

A hypothesised common ancestor from which two or more evolutionary lineages diverged.

What are sister taxa?

Two groups that share the most recent common ancestor on a cladogram and are therefore the most closely related groups shown.

How do you determine relatedness from a cladogram?

Groups sharing the most recent common ancestor are considered more closely related than groups whose common ancestor occurs further back.

Does a cladogram show that one modern species evolved from another?

No. A cladogram shows hypothesised common ancestry and evolutionary relationships, not direct ancestry between modern species.

What is a phylogram?

A branching diagram showing evolutionary relationships where branch lengths represent the amount of inferred evolutionary change.

How can molecular sequence data show species relatedness?

Species with fewer differences in comparable DNA sequences are generally inferred to share a more recent common ancestor.

What is evolutionary radiation?

A rapid increase in the number of species or evolutionary lineages from a common ancestral lineage over a relatively short geological period.

What is adaptive radiation?

A form of evolutionary radiation where a lineage rapidly diversifies as populations adapt to different ecological niches.

What causes adaptive radiation?

Ecological opportunity, reduced competition, new habitats or vacant niches can allow a lineage to rapidly diversify.

What is a mass extinction?

A relatively short geological period during which a large proportion of Earth's species become extinct across many different groups.

How can you identify a mass extinction on an evolutionary timescale?

A mass extinction appears as a sharp decline in biodiversity or surviving lineages over a relatively short geological period.

How can you identify evolutionary radiation on an evolutionary timescale?

Evolutionary radiation appears as a rapid increase in biodiversity or evolutionary lineages over a relatively short geological period.

How long has life existed on Earth?

Evidence indicates that life has existed on Earth for approximately 3.5 billion years.

How can mass extinction lead to evolutionary radiation?

Mass extinction can remove competitors and create vacant ecological niches, allowing surviving groups to rapidly diversify.

How does macroevolution result from microevolution?

Microevolutionary changes accumulate over many generations, eventually producing major evolutionary changes such as divergence and speciation.

Explain how the size and the number of quadrats used affect the reliability of data collected when investigating species diversity.

“Using a larger number of quadrats makes the sample more representative of the whole area and reduces the effect of chance, such as a quadrat landing in an unusually species-rich spot, so results are more reliable. The quadrat size must also suit the area and the plants. If quadrats are too small, less common species may be missed and the diversity underestimated. If they are too large, they are time-consuming and counting errors become more likely.”