Other Methods of EvolutionArtificial Selection | Gene Flow | Genetic Drift

Learning Objectives• Describe the process of artificial selection• Explain how gene flow, and genetic drift can

change a gene pool 

Other Methods of Evolution

• Natural selection – the process by which organisms with favorable variations survive and produce more offspring than less well–adapted organisms

• Non-random mating– the selective breeding of organisms in order to increase the frequency of favorable traits– Produces changes in gene pool due to direct

involvement of humans– Has been used for many years

Non-Random Mating (artificial selection)

• Gregor Mendel used non-random mating in experiments with pea plants

• Selects organisms with alleles for desired traits– Plant with fast growth allele bred with plant with

large fruit allele– Some offspring would have both favorable traits

• Hybridization – the breeding of different varieties of organisms

Non-Random Mating (artificial selection)

• Human use– Dog breeding– Agriculture

• Growing crops• Raising cattle

• Drawbacks– Lowers genetic

diversity of population

– Some traits may be lost from population

– Population more susceptible to change• Disease puts entire

population at risk

Artificial Selection

• Examples in agriculture– Cows selected for

milk production– Livestock selected

for size

• Creation of new varieties of food

Artificial Selection

• Examples– Migration– Seed transfer

• Results– Introduces new

alleles into populations

– Increases variation in gene pool

– Variation fuels natural selection and evolution

Gene Flow

• Gene flow – the transfer of alleles from one population to another

• Genetic drift – the process by which changes in allele frequencies occur as a result of random events

– Random events cause allele frequencies to fluctuate unpredictably

– Affects small populations the most• Allele frequency dependent on total alleles in population

Genetic Drift

• Situations that increase effect of genetic drift– Bottleneck effect – a genetic drift as a result of an

environmental change that reduces the original population to one that has a drastically different gene pool• Chance determined which allele frequencies survive

Genetic Drift

• Situations that increase effect of genetic drift

• Isolated population composed of random individuals

• Founder effect – a genetic drift as a result of a portion of a population becoming isolated and having a drastically different gene pool from the original population– Some alleles overrepresented– Some alleles not present

Genetic Drift

Learning Objectives• Describe the process of artificial selection• Explain how gene flow, and genetic drift can

change a gene pool 

Other Methods of Evolution