Final: Population Genetics Flashcards
Calculating Genotypic frequencies
Number of individuals possessing the genotyp divided by the total number of individuals in sample.
f(AA)=#AA individuals/N
N: total # of individuals
f: freq each genotype
Calculating Allelic Frequencies
Numbers of copies of a particular allele present in a sample divided by total number of alleles
Freq of allele=# copies of the alleles/# copies of all alleles at the locus in a population.
Hardy-Weinberg Law
Assumption: (5)
Prediction 1:
Prediction 2:
Assumption: population is large, randomly mating, not affected by mutation, migration, or natural selection.
Prediction 1: The allelic frequencies of a population do not change.
Prediction 2: The genotypic Frequencies stabilize.
p2:
q2:
2pq:
p2: homozygous dominant allele pair frequency
q2: homozygous recessive allele pair frequency
2pq: heterozygous allele frequency
Population
a group of interbreeding, sexually reproducing individuals with a common set of genes.
Genetic variation
variation in alleles - sequence variation / structural changes
caused by mutation
frequencies affected by evolutionary forces.
Calculating frequency of a genotype:
number of individuals with the genotype/ total number of individuals.
How does calculating allele frequencies for genes on the X chromosome differ from genes in the rest of the genome?
Since males only have one X chromosome they will only have 1 allele
If the assumptions of H.W. are true, what does this confer about the next generation?
Genotypic frequencies are predictable for the next generation.
Positive assortative mating:
a tendency of like individuals to mate
Negative Assortative Mating:
A tendency of unlike individuals to mate
Inbreeding
inbreeding is a measure of the probability that two alleles are identical by descent.
Alleles identical by descent
alleles descended from the same copy in a common ancestor
alleles identical by state
alleles that are the same in structure and function but are descendent from two different copies in ancestors.
Inbreeding depression:
increased appearance of lethal and deleterious traits with inbreeding.
Inbreeding increases the percentage of homozygous individuals in the population.
Outcrossing
the avoidance of mating between related individuals.
What is the effect of outcrossing on a population?
there will be more heterozygotes than predicted by the H.W. law
What doe forward and reverse mutations do to allele frequencies?
They can change allele frequencies, but eventually lead to a stable equilibrium if mutation rates remain constant.
Genetic Drift
Changes in allele Frequency
Causes of Genetic Drift
Founder Effect
Genetic Drift
What are causes of genetic drift?
- Founders Effect
- Genetic Bottleneck
Natural Selection: Define Fitness
Is the relative reproductive success of a genotype compared to other genotypes in the population.
- Fitness ranges from 0 to 1.
- to calculate fitness, take the average number of offspring produced by a genotype and divide it by the mean number of offspring produced by the most prolific genotype.
Natural Selection: Selection Coefficient
Is the relative intensity of selection against a genotype.
-Selection coefficient equals 1- the fitness for a particular genotype.
Natural Selection: Directional Selection
A type of selection in which one allele or trait is favored over another.
Natural Selection: Overdominance (heterozygote advantage)
Both alleles are favored in the heterozygote and neither allele is eliminated from the population
Natural Selection: Underdominance:
The heterozygote has a lower fitness than both homozygotes.
-This leads to an unstable equilibrium.
What is the frequency of a recessive allele at equilibrium equal to?
It is equal to the square root of the mutation rate divided by the selection coefficient.
What is the frequency of a dominant allele at equilibrium equal to?
it is equal to the mutation rate divided by the selection coefficient.
Why is the recessive allele dependent on the square root of the mutation rate?
Because a recessive allele will be covered up by a dominant allele. Selection is a little slower. It will work on individuals that are heterozygous dominant.
What are the short and long term effects of MUTATION?
Short: Change in allele frequency
Long: Equilibrium reached between forward and reverse mutations
What are the short and long term effects of MIGRATION?
Short: Change in allelic Frequency
Long: Equilibrium reached when allelic frequencies of source and recipient population are equal
What are the short and long term effects of GENETIC DRIFT?
Short: Change in allelic frequency
Long: Fixation of one allele
What are the short and long term effects of NATURAL SELECTION?
Short: Change in allelic frequency
Long: Directional selection: fixation of one allele.
- Overdominant selection: Equilibrium Reached.
