Evolution as Genetic Change and Speciation

A Population’s Gene Pool A gene pool is all the alleles available in all of the individuals in a population

How do we know a population is evolving? When there are changes in the frequency of alleles in the gene pool (aka Microevolution) When there are changes in the frequency of alleles in the gene pool (aka Microevolution) How do the allele frequencies change? Natural Selection (directional, stabilizing, disruptive, or sexual selection) Natural Selection (directional, stabilizing, disruptive, or sexual selection) Random Change (mutations, genetic drift, or gene flow) Random Change (mutations, genetic drift, or gene flow) Migration Migration

Genetic Drift The random change in the gene pool of a population The random change in the gene pool of a population All populations are subject to genetic drift, but small populations are impacted more All populations are subject to genetic drift, but small populations are impacted more Bottleneck Effect: Occurs when a natural disaster greatly reduces the size of the population and the gene pool (population loses variation) Bottleneck Effect: Occurs when a natural disaster greatly reduces the size of the population and the gene pool (population loses variation) Founder Effect: Occurs when a few individuals from a population colonize an isolated island or new habitat (population loses genetic variation) Founder Effect: Occurs when a few individuals from a population colonize an isolated island or new habitat (population loses genetic variation)

Gene Flow Gene flow occurs when genes are exchanged with another population (ex: migration) Gene flow occurs when genes are exchanged with another population (ex: migration) Gene flow can reduce genetic differences between populations, possibly uniting the gene pool in a single population Gene flow can reduce genetic differences between populations, possibly uniting the gene pool in a single population

Mutations The random change in the DNA of an organism The random change in the DNA of an organism The frequency of a mutation in the population will depend on the effects of natural selection- will it make the individual more likely to survive and reproduce? The frequency of a mutation in the population will depend on the effects of natural selection- will it make the individual more likely to survive and reproduce?

Hardy-Weinberg Equilibrium Evolution will NOT occur (allele frequencies remain constant) if the following conditions are met: 1. Random mating 2. No emigration or immigration 3. Population must be large 4. No natural selection 5. No mutations

Evolution of a Species Biological Species Concept: a species is a population that will interbreed and produce fertile offspring Biological Species Concept: a species is a population that will interbreed and produce fertile offspring When a population evolves enough genetic change (either through natural selection, genetic drift, etc.) that it no longer interbreeds with the original population, it is considered a new species When a population evolves enough genetic change (either through natural selection, genetic drift, etc.) that it no longer interbreeds with the original population, it is considered a new species

An Example of Speciation 1. A species contains one population or several interbreeding populations 2. A barrier comes between the populations 3. Natural selection occurs 4. Barrier is removed, reproductive isolation has occurred, two species now exist

Other Reproductive Barriers Temporal (timing)- different mating seasons Temporal (timing)- different mating seasons Behavioral- different courtship or mating behaviors Behavioral- different courtship or mating behaviors Habitat- Fish living in streams verses open water Habitat- Fish living in streams verses open water Geographic- populations divided by barriers like glaciers, valleys, rivers, etc. Geographic- populations divided by barriers like glaciers, valleys, rivers, etc.