Lecture 23a Flashcards
What is a Population Bottleneck?
This is when something happens, such as a natural disaster, that causes a drastic decrease in the population regardless of genotype.
How do Population Bottlenecks affect random genetic drift?
Population Bottlenecks increase random genetic drift, because the population is often left smaller and more prone to random genetic drift.
What is an example of Population Bottlenecks?
The African cheetah has lost nearly all of its genetic variation due to a bottleneck effect that occurred 10,000 - 12,000 years ago.
What is Migration?
When a small group of individuals separates from a larger population and establishes a colony in a new location.
What are the 2 consequences of Migration?
1) Founding population will have less genetic variation than the original population.
2) Founding population will have different allelic frequencies from the original population due to chance.
What is an example of the Founder Effect?
The Old Order Amish of Lancaster County, PA.
A population of 8,000 arose from just 3 couples that immigrated to the US in 1770.
How does the Founder Effect impact genetic diseases?
Genetic diseases can be more common due to low genetic variability.
What is an example of how the Founder Effect impacts genetic diseases?
The frequency of Ellis-Van Creveld Syndrome (a recessive form of Dwarfism) is 7% in the Old Order Amish, which is much higher than in any other population.
What is Directional Natural Selection?
Favors the extreme phenotype and may involve a single gene (insecticide resistance in mosquitos) or multiple genes (selection for large size or quickness).
“Selection for one extreme trait, selection against the other extreme trait.”
What is this?
Directional National Selection
What is Disruptive Natural Selection?
Multiple phenotypes are favored in diverse environments. There is not one consensus phenotype.
“Different snail shell colors favored depending on where the snail is.”
What is this?
Disruptive Natural Selection
“Selection for both extremes. Selection against moderate traits.”
What is this?
Disruptive Natural Selection
“Short tails keep predators from catching you on the ground. Long tails are good for balance in trees. Medium tails don’t help.”
What is this?
Disruptive Natural Selection
What is Stabilizing Natural Selection?
The intermediate phenotype has the highest fitness.
“Birds have lower fitness if they lay too many or too few eggs.”
What is this?
Stabilizing Natural Selection
“Selection for moderate traits. Selection against both extremes.”
What is this?
Stabilizing Natural Selection
“Short tails mess up the cat’s balance. Long tails drag on the ground. Medium tails are best.”
What is this?
Stabilizing Natural Selection
What is Balancing Natural Selection?
The rare phenotype has the reproductive advantage over more common phenotypes.
“Bees have been known to favor less the less commonly colored flower.”
What is this?
Balancing Natural Selection
T/F: Balancing Natural Selection may involve a homozygous advantage.
False! It may involve a heterozygote advantage
What is an example of Balancing Natural Selection involving a heterozygote advantage?
For a single gene: the sickle cell mutation
What is Overdominance?
The phenomenon in which a heterozygote is more vigorous than either of the corresponding homozygotes.
Overdominance causes and is an example of what?
Balancing Selection
What type of disorder is Sickle-Cell Anemia?
Autosomal recessive disorder
What do affected individuals of sickle cell anemia produce?
An abnormal form of Hemoglobin
What do HbA and HbS encode?
HbA encodes the normal hemoglobin, hemoglobin A
HbS encodes the abnormal hemoglobin, hemoglobin S
Where has the sickle cell allele most commonly been found?
High frequency in parts of Africa where Malaria is found.
At the molecular level, what is overdominance due to?
Due to 2 alleles that produce slightly different proteins.
What does the eukaryotic parasite Plasmodium do?
Enters HbA HbA red blood cells and multiplies within them.
How does the HbA HbS (heterozygote) genotype protect against Malaria?
Red blood cells of heterozygote are likely to rupture when infected by Plasmodium. This prevents the propagation of the parasite.
What is Assortative Mating?
When sexual reproduction is nonrandom in a population.
What is Positive Assortative Mating?
When individuals with similar phenotypes reproduce with each other.
What is Negative Assortative Mating?
When dissimilar phenotypes preferentially reproduce.
What is Darwinian Fitness?
The relative likelihood that a genotype will survive and contribute to the gene pool of the next generation.
Darwinian fitness is a measure of what?
Reproductive superiority
Basically, the more individuals reproduce = the fitter they are
T/F: Darwinian fitness and physical fitness are the same.
False! They should not be confused with each other. Darwinian fitness is more reproductive superiority.
Fitness is determined by what?
Relative reproductive success
What 2 things determine relative reproductive success?
1) Natural selection- Those individuals that are most adapted to their particular environment will survive and reproduce
2) Differences in mating efficiency and fertility (need the individual to want to have a lot of offspring)
Genotypic classes can be assigned fitness values according to what?
According to their reproductive potential
What fitness value is the gene with the highest reproductive ability given?
1.0
All other genes are in relation to this number, with 1.0 serving as the denominator
Suppose the average reproductive success is:
AA - 5 offspring
Aa - 4 offspring
aa - 1 offspring
What are the fitness values of each?
WAA = 1.0
WAa = 4/5 = 0.8
Waa = 1/5 = 0.2
What variable denotes fitness values?
W
Differences in reproductive achievement can be due to what 3 things?
1) Fittest genotype is more likely to survive
2) Fittest genotype is more likely to mate
3) Fittest genotype is more fertile
