Population Genetics and Risk Assessment Flashcards
What type of alleles can be counted?
Co-dominant alleles -> when the heterozygote alleles can be counted
What is the formula for allele frequency?
Frequency = (Number of alleles) / (Total # of alleles)
What does mutually exclusive mean? Independent?
Mutually Exclusive: Two events cannot occur in a single trial
Independent: One event does not influence the other
How do you determine the allelic frequency in an autosomal recessive condition?
sqrt(q^2), which is the square root of the incidence of affected individuals
How do you determine the allelic frequency of an autosomal dominant condition?
condition frequency = heterozygote frequency = 2pq
assume q = 1
2p = condition frequency
allele frequency = condition frequency / 2
How do you determine the allelic frequency of an X-linked condition?
Frequency in males, since they are hemizygous.
What is the carrier frequency in an X-linked condition?
2pq = 2 (1) (incidence in males). Treat it like an autosomal gene.
What does Hardy-Weinberg work for?
Large populations, with random mating, no migration, mutation, or selection
What is the most important factor which affects allele frequency?
Mutation, which adds alleles to the gene pool and is a source of variability.
What is selection vs fitness?
Fitness = relative rate of reproduction, where 1 is normal
Fitness = 1 - selection
Selection is normal when 0, the higher it is the more you are selected against
Which is an example of heterozygote advantage?
It is when heterozygotes are at a selective advantage in comparison to heterozygous. Sickle cell anemia
What is a balanced polymorphism?
When there is selection in a population against both the presence of an allele and the absence of an allele in heterozygosity (i.e. sickle cell anemia).
What are two mechanisms of genetic drift?
- Founder effect - random subgroup of a population forms a new population, and happens to randomly have a higher incidence of a mutant allele
- Bottleneck - Population is drastically reduced by a natural disaster, and randomly a certain allele is more common than the parent population
What is gene flow? How does this differ from genetic drift?
Movement of alleles into or out of the gene pool resulting in gradual changes in allele frequency, as a result of migration and interbreeding, rather than chance (genetic drift)
What is assortative mating?
When individuals choose a mate based on similar characteristics -> nonrandom
What is the coefficient of relationship (r) and its calculation?
The proportion of genes shared by two related individuals. (1/2)^n based on degree of relatives away. So, second degree relatives = (1/2)^2 = 1/4
What is the inbreeding coefficient (F)? How is it calculated?
The probability that an individual is homozygous (recessive) as a result of consanguinity.
F = 1/2*r.
So for second degree relatives, 1/2 * (1/4) = 1/8, when a guy has sex with his aunt.
When is Bayesian analysis used?
- Diseases with later ages of onset
- X-linked inheritance
- Non-penetrance
- Negative lab results when sensitivity is <100%
What yields the prior probability?
The Mendelian risk calculation
What gives the conditional probability?
The chance of the current condition occurring, given the presupposed mutation is true (i.e. chance of not having breast cancer at age 50 given you have BRCA1 mutation, and 59% of people would have cancer at this point)
What is the joint probability?
Prior * conditional probability
What is the posterior probability?
Joint probability, normalized with both conditions.
