The Genetic Basis of Evolution

Themes Population gene pools evolve, not individuals Most populations have a large amount of genetic variation Genetic variation is the pre-requisite for evolution The mechanism of evolution can either be because of selection or because of chance

Sources of Genetic Variation 1.Sexual Reproduction *meiosis and independent assortment *combines genes in different ways 2. Mutation *can create new beneficial genes/traits via deletion, substitution, insertion or inversion of DNA bases

3. Exon Shuffling can create new genes/traits by combining mini- genes in new ways Exons 1,2,3 code for gene 1 (normal) Exons 4,5,6 code for gene 2 (normal) Other combo’s may combine to produce new genes DNA intron

4. Gene Duplication & Divergence multiple copies of the gene can be “played” with. One copy will still function in the “old” way while mutated copies can serve as trials for potentially new beneficial genes Gene 1 Gene 2 Gene 1 Gene 2 Gene 1 Gene 1A

Agents of Evolution There are 5 agents of Evolution – 5 things that can cause gene frequencies to change over time: 1.Natural Selection (and artificial selection) 2.Mutation (& exon shuffling & gene duplication/diver.) 3.Gene Flow (migration) 4.Non-random mating (sexual selection) 5.Genetic drift

Natural Selection  Environmental changes can cause gene frequencies to change.  Ex. Polluted forests favoring black moths over white ones  It is the main mechanism of evolution, but not the only mechanism

Mutation (New Variation)  Mutation, exon shuffling and gene duplication & divergence can create new genes  Though rarely, new genes will occasionally offer an adaptive advantage  In this case, the new genes will be passed on to future generations and will accumulate and become more abundant than “old” genes

Gene Flow migration can cause changes in gene frequencies Grey Black Grey Black

Non-Random Mating  Also known as Mate Selection or Sexual Selection  Organisms with desired characteristics are selected  Skews gene frequencies: over time the desired characteristic increases in number

Genetic Drift  Unexpected random changes in gene frequency that occur because of rapid reduction in population size:  The smaller the population, the greater the role that genetic drift plays  Two mechanisms:  Population Bottleneck  Founder Affect

Population Bottleneck A large portion of the population is wiped out, leaving behind a very small population (ex. Natural disaster) Grey Black Grey Black Survival of the Lucky, not the Fittest

Founder Effect A small portion of the population breaks away from the parent population and becomes isolated from it (ex. Hutterites) Grey Black Grey Black