Population Genetics Flashcards
Study of allele frequencies in a population
Population Genetics
All the alleles in a population
Gene Pool
A focus of population genetics:
To understand the forces that change the gene pool
Why measure genetic variation?
- microevolution
- genetic engineering
- infer diversity in preparation for selective pressure
- inheritance patterns (ex. founder mutation)
- genetic counselling/ disease probability
- adaptation
- history of interbreeding
The proportion of a specific genotype within a population.
-ranges from 0 to 1.
Genotypic frequency
Genotypic frequency example: Scarlet tiger moth wing pattern gene (B)
Frequency of BB genotype?
Genotype: BB; # individuals: 452; total # in population: 497
F(BB)= #of individuals/total # in population
Frequency=0.909
Portion of an allele within a population.
Allelic frequency
Allelic frequency example: Scarlet tiger moth
What is the frequency of the B allele?
F(B)= #of a specific allele/total # of all alleles
=(2BB)+(1Bb)/2(total # individuals)
Frequency of dominant allele (A)
p
Frequency of recessive allele (a)
q
Frequency of heterozygous allele (Aa)
2pq
Frequency of Homozygous dominant (AA)
p^2
Frequency of Homozygous recessive (aa)
q^2
p+q=1
Allelic frequency shortcut
Allows us to calculate allelic and genotypic frequencies in the absence of evolutionary forces.
Hardy-Weinberg Law
Assumptions about the population for Hardy-Weinberg to work:
1) No migration
2) Large population
3) Random mating
4) No mutation
5) No natural selection
- Genetic equilibrium; the frequency of alleles do not change over time.
- Gives us an idea about genetic variation
Hardy-Weinberg Law
p^2 + 2pq + q^2
Hardy-Weinberg Equation
-Like crossing population with itself
-Each individual passes both alleles that it possesses with equal frequency.
(p+q)(p+q)=p^2+2pq+q^2
Derivation of Hardy-Weinberg Law
If Hardy-Weinberg assumes no evolutionary influences, then what is its purpose?
- Standard of comparison
- Predictor
- Control
Example: Study geographic-dependent allelic variation
- Allele frequencies vary for populations separated by space across geographic transect.
- Cline
Gradient for allele frequencies that changes in a systematic way according to the physical attributes of the environment.
-Blue mussles and aminopeptidase: LAP
North to South=increasing frequency for LAP94
*LAP94 allows for survival in lower salinity.
Cline
How is genetic variation measured in a lab?
-Measure gene product
How is genetic variation measured at the DNA level?
-Examine nucleotide sequence directly (BLAST) after PCR
-Examine RNA products (sequence & size differences)
-Look for polymorphism
(For Repeats)
*visualize by microscopy
*PCR & look for size differences on gel
(For SNPs)
*RFLP analysis
Sequence changes between individuals.
Polymorphisms
- Look for single nt. changes in DNA
- a SNP has changed a restriction enzyme site.
RFLP analysis
Forces that change allele frequencies:
- Mutation
- Natural Selection
- Genetic Drift
- Migration
Converts one allele to another
-New allele may be neutral, can be detrimental or advantageous, thus subject to natural selection.
Mutation:
Frequency of alleles in a population is determined by interaction of mutation rates and natural selection
Individuals with alleles that confer an advantage in the environment, produce more offspring on average than other in the population.
-Frequency of alleles that confer survival and reproduction advantages increase population over time.
Natural Selection
The relative reproductive ability of a genotype.
Fitness
Selective mating type of the same phenotype.
Positive
Selective mating type of the opposite phenotype.
Negative
Changes in allele frequencies due to random sampling.
-reduces genetic diversity
Genetic Drift
Contributes to genetic drift; when population is drastically reduced in #.
Bottleneck
Contributes to genetic drift; when a population is established from a small # of breeding individuals.
Founder Effect
Types of migration
Immigration
Emigration
Type of migration that introduces new alleles
Immigration
Type of migration that takes away alleles
Emigration
When an individual migrates and contributes their alleles to the gene pool of the receptive population.
Gene Flow
