1. How Populations Evolve

2. Things We Will Know How to summarize Hardy Weinberg principal
Describe the five forces that cause genetic change in a population
Identify why selection against unfavorable recessive traits is slow
Contrast Directional and Stabilizing Selection

3. Hardy-Weinberg Principle
G.H. Hardy and Wilhelm Weinberg researched to understand trait frequencies
Found that dominant traits do not overcome recessive traits within populations.
Populations typically do not change traits drastically unless acted on by an evolutionary force within the population.

4. Hardy-Weinberg Principle
What are the five forces that can cause populations to evolve?
Populations
Can evolve through
Gene mutation
Gene flow
Nonrandom mating
Natural selection
Genetic drift

5. Gene Mutations Gene mutations are very slow
They mutate 1 to 10 times per 100,000 cell divisions
Not all gene mutations are result in phenotypic changes, Still, some do cause change. Example: Sickle Cell Anemia
Mutation is a source of variation in populations

6. Gene Flow Migration is the major form of gene flow.
Gene flow occurs because new individuals (immigrants) add alleles to a population
Gene flow also occurs when individuals depart (emigrants) taking important traits away.

7. Nonrandom Mating Mating with individuals nearby is nonrandom mating.
Inbreeding is a way to keep traits in a population from changing; lower frequency of heterozygous individuals
Another example of nonrandom mating is when females choose their mates based on popular or beneficial traits

8. Genetic Drift
Natural disasters can wipe out large numbers within a population
Losing large numbers causes loss of strong and beneficial traits.
Because Natural Disasters are Random:
A random change in traits within a population is called a Genetic Drift

9. Natural Selection Survival of the FITTEST
Traits that are beneficial allow certain individuals to survive.
Certain traits are not favorable and the animals containing those traits usually do not get to reproduce
For example:
Sickle Cell anemia is slowly declining in the U.S. because it is rarely passed on to another generation.

10. Slowly Removing Unfavorable Traits
Tsar of Russia Alexi Nikolayevich had a homozygous recessive trait for hemophilia
He died early and never passed one his traits, but all of his sisters were carriers
Did the trait die with him?
NO, every sister passed on the trait for several generations, but no one knew because it was not a phenotypic trait

11. Distribution of Traits
Polygenic traits are traits that are influenced by dozens of genes.
Polygenic traits cause normal distribution or an average curve among populations
Usually called a Bell Curve

12. Contrasting Selection
Directional selection is when one an extreme trait is favored and the opposite extreme trait is not. One extreme individual lives to reproduce while the other is lost in history
Stabilizing Selection is when neither extreme traits survive, but the average individuals survive to reproduce

13. Directional Selection
Stabilizing
Selection