1. Introduction to Evolution
Refer to Section 17.1 (pages )
Review vocabulary on PEHSBiology Quizlet

2. What is evolution? Remember:
Evolution: any change in the relative frequency of alleles in the gene pool of a population over time.
Remember:
Natural selection affects individuals
BUT Populations of individuals evolve

3. Definitions to know Allele: different forms of genes
gene pool: all of the genes, including the different alleles that occur in a population.
relative frequency: the number of times a particular allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur.
Population: a group of organisms of the same species

4. Gene Pool Illustration
Example: this diagram shows the gene pool for fur color in a population of mice.
Remember…
Genotype: the genetic makeup
Phenotype: the physical characteristics

5. Natural Selection: the mechanism of evolution
Natural selection: organisms with variations most suited to their local environment survive and leave more offspring.
*Natural selection on acts on HERITABLE traits!
In natural selection, the environment—not a farmer or animal breeder—influences fitness.

6. Natural selection occurs in situations where:
more individuals are born than can survive (the struggle for existence),
there is natural heritable variation (variation and adaptation), and
there is variable fitness among individuals (survival of the fittest).

7. 1. The Struggle for Existence
If more individuals are born than can survive, members of a population compete to get:
Food
Places to live
Places to put waste.
Competition increases when resources are limited .

8. 2. Variation and Adaptation
Individuals have natural variations in their heritable (able to be passed on to the next generation) traits
2 Main sources of genetic variation (the raw material for evolution)
Mutations: changes in genes (bacteria mutate often & quickly)
Genetic recombination during sexual reproduction
ADAPTATION: a variation that helps an organism survive and reproduce in its environment

9. Examples of Adaptations

10. 3. Survival of the Fittest
Fitness: how well an organism can survive and reproduce in its environment.
High fitness = they survive and reproduce.
Low fitness = will either die or not reproduce
Survival: reproducing and passing adaptations on to the next generation.
Differences in adaptations affect an individual’s fitness.

11. Natural Selection of Single-Gene Traits
Example: Lizard body coloration
Normal color is brown; red and black mutations appear
Allele for red makes lizard an easy target for predators
Over time, this allele will…
Allele for black makes it easier for the lizard to absorb sunlight and then move faster
Initial Population
Generation 10
Generation 20
Generation 30
80% brown
70% brown
40% brown
10% red
0% red
10% black
20% black
30% black
60% black