1. Evolutionary Processes
Chapter 25
Evolutionary Processes

2. Key Concepts
The Hardy-Weinberg principle acts as a null hypothesis when researchers want to test whether evolution or nonrandom mating is occurring at a particular gene.
Each of the four evolutionary mechanisms has different consequences. Only natural selection produces adaptation. Genetic drift causes random fluctuations in allele frequencies. Gene flow equalizes allele frequencies between populations. Mutation introduces new alleles.

3. Key Concepts, cont’d
Inbreeding changes genotype frequencies but does not change allele frequencies.
Sexual selection leads to the evolution of traits that help individuals attract mates. It is usually stronger on males than on females

4. Hardy-Weinberg Principle
A mathematical model to analyze alleles in a population
p2 + 2pq + q2 = 1
p + q = 1
p symbolizes frequency of one allele (A1) and q symbolizes frequency of another allele (A2)
frequency x 100 = %
pp = homozygous for A1, qq = homozygous for A2, and pq is heterozygous

5. Evolutionary Mechanisms
Natural Selection- alleles are favored, dependent on the environment
Genetic Drift- any change in allele frequencies in a population that is due to chance
Gene Flow- movement of alleles from one population to another
Mutation- changes in the makeup of chromosomes or in specific DNA sequences

6. Natural Selection
Directional Selection- selection where the population goes to an allele away from the average
Stabilizing Selection- selection where more of the population express the average allele
Disruptive Selection- population where the population splits into two alleles different from the average

7. Genetic Drift
Random elimination of a portion of the population (not dependent on traits)
Causes:
Bottleneck Effect- random death
Founder Effect- colonizing in another location

8. Evolutionary Mechanisms
Gene Flow: migration of a members of the population to another population
Mutations: change in the DNA to produce new traits

9. Inbreeding
Inbreeding- increases homozygous dominant and recessive genotypes
Sexual Selection- acquired traits by males increase rate of reproduction
Increase the frequency of the trait in a population