Biology Unit 2- Evolution

What is evolution?

Evolution is the change in the frequency of genetic variation within a biological population over time (across successive generations)

What are the two forms of evolution?

Microevolution: small scale changes in allele frequencies within a population over a short time

Macroevolution: large scale changes at or above the species level over geological time

Why is genetic variation in a population a prerequisite for evolution?

It provides raw material that natural selection and other mechanisms use to change allele frequencies over time

What is Darwin’s theory of natural selection?

All life develops through the natural selection of small, inherited traits that help organisms survive and reproduce

What factors can produce genetic variation in a population over time?

Mutations: Create new alleles by changing DNA sequences (introduce fresh genetic material into gene pool)

Gene flow (migration): movement of individuals/genes between populations introduces new alleles/changes their frequencies

What other factors affect genetic variation/evolution?

Genetic drift: Random changes in allele frequencies (chance events or bottlenecks)

Natural selection: environmental pressures favour certain traits, changing allele frequencies

Sexual reproduction and recombination: crossing over and independent assortment during meiosis reshuffles alleles into unique combos

Why are genetic drift and gene flow considered mechanisms of evolution?

Both directly change allele frequencies within populations

What is the founder effect?

when a small group becomes isolated from a larger population and establishes a new population with a different gene pool

Example: British colonists carried a recessive allele for retinitis pigmentosa; the allele became common among decedenants on Tristan da Cunha

What is the bottleneck effect?

A population experiences a severe reduction in size (due to natural disasters, harvesting, disease), causing some alleles to become overrepresented while others many be lost entirely

Example: Vancouver island marmot population size declined, resulting in reduced genetic variation

What is an example of gene flow affecting local adaptation?

Lake Erie water snakes have different colours, which affects how well they camouflage in different environments has different and colours, making it harder for them to camouflage

What is an example of gene flow improving adpaation?

Worldwide spread of insecticide-resistance alleles in the mosquito culex pipiens improves resistance to insecticides

What is the process of natural selection?

Variation: Living things within a species have different traits (colour, size, shape), coming from random genetic mutations

Elimination: Organisms with disadvantageous traits die or fail to reproduce

Reproduction: Survivors reproduce and pass on advantageous heritable traits

Result: beneficial traits increase in frequency over generations

What are the three patterns of natural selection?

Directional: favours one extreme phenotype— population average shifts in one direction

Disruptive: favours both extreme phenotypes— selects against intermediate/average forms, splitting population into groups

Stabilizing: favours average/intermediate phenotypes— selects against extremes and reduces variation

What are the main features of natural selection?

Not random: environmental pressures determine which traits are favoured

Leads to adaptation: favoured traits become more common

Dynamic: changing environments create new selection pressures

Populations evolve, not individuals: individuals survive/reproduce differently, bute allele frequencies change across generations in populations

What is homology and analogy?

Homology: Similarity in structure due to shared ancestry; homologous structures may have different functions in different organisms

Analogy: Similarity in function due to convergent evolution; analogous structures evolved independently in different lineages

Why is natural selection the only mechanism that leads to adaptive evolution?

It favours heritable traits that improve survival and reproduction, increasing their frequency in a particular environment