Download Forces of Evolutionary Change

Forces of
Evolutionary Change
Forces of Evolutionary Change
• All of the factors that influence evolution and
lead to new species relate to one of 4 main
forces of evolution/change.
• Those forces of change are:
– Genetic Mutations
– Gene flow (Genetic Migration)
– Genetic Drift
– Natural Selection
Forces of Evolutionary Change
• So…HOW do these forces actually lead to
evolution??
• The four forces lead to changes in allele
frequencies in a population
• This leads to changes in the genetic variation
of the population
Forces of Evolutionary Change
What are allele frequencies??
1. A frequency is how often something occurs
2. Written as a percent (e.g. 50%) or proportion (e.g. 0.5)
3. Allele frequencies show how genetically diverse a
population is.
More alleles  More diverse!
More even percentages of those alleles 
More diverse!
Genetic Mutations
1. Random process
2. Change in the genetic code
(DNA)
3. These mutations are passed
from parent to offspring
4. Mutations can be detrimental
(bad) or advantageous (good)
Gene Flow / Genetic Migration
1. Genes can move into or out of a population
2. As organisms move, they bring their genes
with them
3. This leads to new allele combinations in the
population
Gene Flow / Genetic Migration
Gene Flow / Genetic Migration
Applies to plants, too!
Pollen + seed movement…
Effects of Gene Flow on Evolution
Gene flow impacts evolution in multiple ways:
1. Introduces alleles into a population
2. Increases genetic variation
Effects of Gene Flow on Evolution
Gene flow impacts evolution in multiple ways:
1. Introduces alleles into a population
2. Increases genetic variation
3. MORE gene flow = Reduces the chance of
new species forming
4. LESS gene flow = Increases the chance of new
species forming
Genetic Drift
1. Random change in allele frequencies
2. Due to “chance”
3. Has the greatest impact on small populations
Genetic Drift
Original allele
frequencies in
a population
**Random Event**
Changed allele
frequencies
due to random
event
Genetic Drift
Founder Effect: a few individuals start a new
population with different allele frequencies
Natural Selection
1. Survival of the fittest
2. NOT random!
Natural Selection
1. Survival of the fittest
2. NOT random!
3. Individuals with beneficial adaptations are more
likely to survive and reproduce.
4. Results in a change in allele frequencies over
time:
– Beneficial alleles INCREASE
– Detrimental alleles DECREASE
Adaptive Traits
Adaptation:
Trait or behavior that
helps an organism
survive and reproduce
in its environment
Result of Natural Selection
Natural selection results in a change in alleles
frequencies!
Sexual Selection
• Type of natural selection  One sex prefers
certain characteristics in the other sex
Let’s put it all together…
• Which forces of evolutionary change
INCREASE genetic diversity in a population?
• Which forces of evolutionary change
DECREASE genetic diversity in a population?
Let’s put it all together…
• Which forces of evolutionary change
INCREASE genetic diversity in a population?
Mutations and Gene Flow
• Which forces of evolutionary change
DECREASE genetic diversity in a population?
Genetic Drift and Natural Selection
What happens when allele frequencies change so
much over time that the population looks and
behaves really different??
Speciation
• A species is a group of
organisms that breed and
reproduce fertile
offspring
• Speciation is the
formation of a new
species
Speciation
• Causes of speciation
– Reproductive isolation
– Behavioral isolation
– Geographic isolation