1. Lesson Overview
17.1 Genes and Variation

2. Genotype and Phenotype in Evolution
Population – mating group of organisms of the same species
Gene pool – all genes (and their alleles) present in a population
Allele frequency - # of times allele occurs in a population
Changes as population evolves over time
Natural selection operates on individuals, but causes a change in the allele frequency

3. For example, this diagram shows the gene pool for fur color in a population of wild boar.

4. Populations evolve not individuals!!
Populations and Gene Pools
Evolution-change in the relative frequency of alleles in the gene pool of a population over time.
Natural selection operates on individuals, but causes a change in allele frequencies in populations.
Populations evolve not individuals!!

5. Sources of genetic variation
Main source of genetic variations in populations is mutations!!
They occur randomly
Only heritable mutations matter for evolution
Other sources of variation include:
1. Genetic recombination- crossing over and independent assortment in meiosis
2. Lateral gene transfer- (bacteria only) Bacteria swap plasmids between members of the same generation, then pass them to
their offspring

6. Natural Selection & Phenotype
An organism’s genotype and environmental conditions makes up its phenotype.
Natural selection operates on variation in organisms’ phenotypes.
Phenotypes that are better suited for the environment will have higher fitness

7. Single-Gene and Polygenic Traits
Number of phenotypes for a trait depends on how many genes control the trait.
Single-gene trait – trait controlled by one gene.
Ex. Banded or un-banded shell NS on these traits leads to changes in allele and phenotypic frequencies.

8. Polygenic trait – trait controlled by two or more genes.
Ex. Height in humans.
NS on these traits affects
fitness of phenotypes.

9. NS on polygenic traits leads to selection in populations
When NS on polygenic traits affects the fitness of phenotypes, it leads to selection:
1. Directional selection
2. Stabilizing selection
3. Disruptive selection

10. Types of selection in populations
Directional selection – organisms at one end of The curve have a higher fitness than those in the middle or at the other end
Stabilizing selection – organisms in the Center have highest fitness
Disruptive selection – organisms at the ends of curve have highest fitness

11. NS is not the only source of change in allele frequencies
Genetic drift – change in allele frequency that occurs in small populations due to random chance
*Genetic bottleneck – change in allele frequency following a dramatic reduction in population size
*Founder effect – change in allele frequency following migration of a small subgroup out of the population to start a new population