UNIT 4 TOPIC 2

What is microevolution?

Small‑scale changes in allele frequencies within a population over generations.

What is macroevolution?

Large‑scale evolutionary change above the species level, including speciation and major transitions.

How do microevolution and macroevolution differ?

Microevolution = allele frequency changes; macroevolution = accumulation of microevolution leading to new species and higher taxa.

How do mutations drive microevolution?

They introduce new alleles, creating genetic variation for selection to act on.

How does gene flow cause microevolution?

Movement of alleles between populations changes allele frequencies and reduces divergence.

What is genetic drift?

Random changes in allele frequencies, strongest in small populations (e.g., bottleneck, founder effect).

What is natural selection?

Individuals with advantageous heritable traits survive and reproduce more, increasing allele frequency of those traits.

What is stabilising selection?

Selection favours intermediate phenotypes, reducing variation.

What is directional selection?

Selection favours one extreme phenotype, shifting the mean.

What is disruptive selection?

Selection favours both extremes, increasing variation and potentially leading to speciation.

What is divergent evolution?

Unrelated species evolve similar traits due to similar selection pressures (e.g., sharks & dolphins).

What is parallel evolution?

Related species evolve similar traits independently due to similar environments.

What is coevolution?

Two species reciprocally influence each other’s evolution (e.g., predator–prey, pollinator–flower).

How does geographic isolation lead to speciation?

Physical barriers prevent gene flow → populations diverge → allopatric speciation.

What is temporal isolation?

Populations breed at different times → reduced gene flow.

What is spatial isolation?

Populations occupy different microhabitats → reduced interaction.

What is allopatric speciation?

Speciation due to geographic separation.

What is sympatric speciation?

Speciation without physical separation (e.g., polyploidy in plants).

What is parapatric speciation?

Adjacent populations diverge due to different selection pressures and limited gene flow.

Why does low genetic diversity increase extinction risk?

Reduced ability to adapt to environmental change; higher susceptibility to disease; inbreeding depression.

How does comparative genomics support evolution?

Closely related species share more DNA sequences; conserved genes indicate common ancestry.

How are conserved sequences used to date divergence?

Mutations accumulate at predictable rates; fewer differences = more recent divergence.

What is evolutionary radiation?

Rapid diversification of species from a common ancestor (e.g., Cambrian explosion).

What is a mass extinction?

Sudden global loss of many species, opening niches for adaptive radiation.