Population risk Flashcards
Explain determination of genotype frequency from Allele frequency
A given population has 2 alleles call P and Q for a specific gene:
- If laboratory testing shows that the frequency of allele P is 0.7
- Then the frequency of allele Q must be 0.3
The sum of frequency of the alleles=1= p+q
What is the hardy weinberg equation?
P2 + 2pq+ q2
p- the. Functional or commonly found allele
q- be the disease causing, or rarely found allele
How are individuals affected by autosomal recessive diseases (frequency) found by the hardy Weinberg equation?
Affected individuals are represented on the HW equation by q squared
So the incidence of affected individuals is q squared
How we can derive allele frequency from the. Incidence?
The frequency of the disease causing allele (q) is derived from the incidence (=I) of the disease in the population
If q2 is the proportion of people that have the disorder, then it is the same as the incidence, so q= sqrt of I
This relationship allows the estimation of the allelic and carrier frequencies in autosomal recessive (AR) disorders
Incidence is obtained from epidemiology
For most autosomal recessive disorders, p=1 because…
Since q is a very small number
- As long as q is less than 5% of the total alleles in the population, this simplification is valid enough for our estimations
- Students should commit this simplification step to memory
Hence 2pq = 2q, making the calculation easier
What is allele frequency ?
- Proportion of chromosomes that contain a specific allele
- individuals will have 2 alleles for every autosomal locus
- Different alleles at a genetic locus can be measured or stimated in various way
- genetic testing (directly determining allele)
- Phenotypic analysis and epidemiology (from incidence rates)
You must be able to interpret and derive allele frequency if given data about genotype frequency
-This is straight forward
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