The Evolution of Populations Modern Synthesis Theory

Important Terms… Microevolution: Change on a small scale (changes to a population gene pool from generation to generation)

Population: Local group of individuals that can breed & produce viable offspring Gene Pool: The genes in a population (all alleles/traits) Darwin’s theories were based on natural selection (but he didn’t know ANYTHING about genetics yet!!)

Modern Synthesis Theory Based on Darwin’s ideas of natural selection AND Mendel’s ideas about heritability Population genetics studies how populations change genetically over time Modern Synthesis used ideas from many scientific areas to generate a complete view of evolutionary theory

How can populations change genetically?? Natural Selection- individuals who are better suited to their environment will survive to reproduce (higher fitness) Genetic Drift- Chance events that change a gene pool (usually in small populations)

Bottleneck- Sudden change (ex Bottleneck- Sudden change (ex. Fire/flood) dramatically reduces population size (by chance, certain alleles survive!)

Founder Effect-Some individuals (by chance) become isolated from larger population (Ex. Darwin’s finches; island colonies) Gene Flow- Introduction of new alleles from immigrant population; can amalgamate different populations… look at humans as an example! Think how you can create a simple diagram to illustrate genetic drift vs gene flow & add this to your notes.

How does Natural Selection Work?? Organisms with adaptive advantage over others Increases the fitness of organisms Fitness: the ability to survive to reproduce Fitness is relative to the environment which a population lives in… this can change quickly or slowly over time, putting pressure on a population to change too!

Modes of Selection

Directional Favours traits at ONE extreme

Stabilizing Extremes are diminished; intermediate traits are seen

Disruptive Both extremes (almost opposites) are favoured as traits

Sexual Selection Animals (usually the females), may be preferential towards specific traits in males These males mated with more frequently, passing favoured trait onto male offspring Ex. Colourful plumage in male birds

In intrasexual selection, stronger more aggressive males are typically more successful reproductively