A random change in allele frequencies from generation to generation
Example: tornado or extreme rain killing a colony of ants
How does population size affect random evolutionary change?
Results in allele fixation over time
Based on your population genetics lab, which of the following best defines allele fixation?
B) A single allele is the only allele remaining in the population
In your log simulations (genetic drift), which simulation resulted in the most rapid allele fixation?
A) Starting population of 10 mussels
Larger populations -> less subject to changes in genetic diversity over time due to random chance.
Random chance has a much greater affect on small populaitons
How does genetic drift reduces genetic diversity?
On average, allele fixation occurred more quickly in the smaller population
Inference: smaller populations more likely to lose genetic diversity due to drift
Why is the loss of genetic diversity in a population evolutionarily important? Why do we care?
Limits future adaptation of populations to changing environments -> selection can act only on existing variation
We care for managing endangered species -> represented by very small populations
--Genetically homogeneous populaitons at risk of extinction if NONE have alleles that allow survival under a new environmental pressure
Heterozygosity (H)
Measures the probability of drawing 2 different alleles from the gene pool of a population (also called gene diversity)
Which of the following would correctly calculate heterozygosity, given:
p2: the probability of drawing two dominant alleles
q2: the probability of drawing two recessive alleles
C) H= 1-(p2+q2)
What does higher heterozygosity mean?
Greater gene diversity
Which of the following population allele frequencies would have the highest heterozygosity?
B) p=0.5, q=0.5
The greatest probability of getting 2 different alleles is when the alleles are equal in the population
Given your knowledge of drift, which of the following is the best prediction, when comparing smaller and larger conservancy sizes?
A) Heterozygosity will be highest in larger conservancies and lowest in smaller conservancies
Can a population with NO heterozygotes have heterozygosity?
No
Fragmentation
Previously large, continuous habitat broken into smaller unconnected pieces
Why would habitat loss and fragmentation affect genetic diversity?
Smaller habitats support smaller populations -> more likely affected by drift
Disconnected habitats limit gene flow between populations
What does this figure indicate?
Buffalo populations on smaller conservancies have lower genetic diversity than populations on larger conservancies
-associated with population size supported by different territory sizes
Habitat fragmentation began only ~100 years ago- what does this suggest for future genetic diversity of buffalo?
Likely to decline further
What do you do as a conservation manager for cape buffalo?
Establish ecological corridors between conservancies to maintain gene flow between populations
Try to make less smaller conservancies and more larger conservancies
Bottleneck Effects
Occurs when an environmental/human catastrophe decimates a large percent of the population
Population size may rebound, but genetic diversity is subset of pre-catastrophe levels
Is there hope for cheetahs in relation to their territory and mating system?
Females mate with multiple males because their large territory provides them with access to many mates.
Females can bear cubs from different males within the same litter
How would females mating with multiple males affect maintenance of gene diversity in cheetahs?
C) If females mate with multiple males, it is more likely that genetic diversity of the population will be maintained
Mating with multiple males increases of maintenance of gene diversity which makes the population more resilient to environmental pressure
Founder Event
A new, smaller population of "founders" break-off from the original population
Founding population usually less genetically diverse
Founder effects
Occur if the new population has lower genetic diversity than the original population
With founder effects: lower genetic diversity of founding population -> passed to offspring
Porphyria variegata
Results in abnormal heme molecules
The mutation can be traced to a single couple who moved to South Africa in late 1600s
Founding population reproduced within themselves -> founder effects
Gene Flow
Introduction or removal of alleles from a population -> change allele frequencies
Mutation
A permanent, random change in the DNA sequence of an organism
Ultimate source of all variation that evolution acts on
May or may not result in new phenotype
Why bed bugs are a huge problem in central OH?
Change in DNA that altered 2 of ~2000 amino acids in bed bug sodium pore -> 250x more resistant to pyrethroid pesticide
This mutation is quite recent
Which of the following best explains why the bed bug mutation occurred?
D) Neither A nor B explain why this mutation occurred
Genetic Polymorphism
Having multiple different alleles for a gene
Function of the rate of drift and mutations
Why do we still have variation if drift decreases heterozygosity over time?
Larger populations: less sensitive to drift -> would take a very, very long time to lose variation
Mutation increases polymorphism
Gene flow between population can increase variation
