Population Genetics Flashcards
(39 cards)
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
