Transcript microevolution - Wikispaces : AaronFreeman

Microevolution
What is Microevolution?
Change in a
populations
alleles over a
period of time
Calculate allele
frequencies
Allele
Two different forms of a gene (portion of DNA
that codes for a trait)
Three different combinations
of Alleles
Homozygous Dominant: DD
Heterozygous: Dd
Homozygous Recessive: dd
Allele Frequencies
A measure of
how often
(frequency) an
allele is
apparent in a
population.
What is Natural Selection?
“Survival of the
Fittest”
The best
adapted
organism will
survive and
pass traits onto
offspring
Observation #1
Every population has the ability to grow
Observation #2
Every population has limited resources
Conclusion #1
Competition for resources
Hyena
Observation #3
Every individual in a population is different
in structure and behavior. Ex-pattern,
speed, agility, etc
Conclusion #2
Natural Selection-Survival of the Fittest:
Best adapted organism will survive
Observation #4
Survivors will
pass their traits
on to their
offspring.
Conclusion #3
Evolution has occurred. There could be a
change to the population.
Example #1
Peppered Moth http://www.youtube.com/watch?v=LyRA807djLc
Directional Selection
• One extreme is selected for causing the
other extremes to be selected against.
Example Directional Selection:
Peppered Moths
Black were selected
against leaving peppered
around
When env conditions
changed, selection
shifted against white
Example #2: Pesticide Resistance
• When insecticides are first used, vulnerable insects
die.
• Few individuals that are “immune” to the
pesticide, survive and live to pass on that trait.
Example #3: Antibiotic Resistance
• Antibiotics first came into use in the 1940s. Overuse has led to increase
in resistant forms of bacteria.
• Over-prescribed antibiotics include penicillin and streptomycin.
• Overuse of antibiotics has selected for resistant strains, which now
threaten to become more predominant than the susceptible ones.
Stabilizing Selection
• Heterozygote advantage
• Intermediate forms are favored while the
extremes are selected against.
Stabilizing Selection Example #1: Human Babies
• Humans who weigh about seven pounds at birth have the greatest
survival chances. Extreme weights are lower survival rate.
Example #2
• Siberian Husky is a medium dog weighing between
35-60lbs.
• These dogs have strong pectoral and leg muscles
allowing it to work through the snow.
• How is this an example of stabilizing selection?
Disruptive Selection
• The intermediate (middle) is selected against while
both extremes are selected for.
Disruptional Selection Example
Butterflies selected for..
African butterfly ranges in color from orange to blue.
Orange + Blue mimic other butterflies that when eaten, taste bitter.
Birds eat intermediates when feeding to avoid bitter taste.
Selected against…….