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#1
05-07-2015
 USMLE Forums Scout Steps History: Not yet Posts: 12 Threads: 4 Thanked 1 Time in 1 Post Reputation: 11
Genetics doubt

In genetics when they say incidence/prevalence of a disease is 1/2500 or 1 in 2500, what does tell us exactly ? Q or Q2 (squared )

And coming to the X linked recessive disease in males .
For eg : If the incidence of DMD in North America is about 1/3000 males. On basis of the figure , what is the gene frequency of this mutation.
I know the answer but I would be grateful if someone could please explain it.
Thanks

#2
05-07-2015
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Quote:
 Originally Posted by akhil4eva In genetics when they say incidence/prevalence of a disease is 1/2500 or 1 in 2500, what does tell us exactly ? Q or Q2 (squared ) And coming to the X linked recessive disease in males . For eg : If the incidence of DMD in North America is about 1/3000 males. On basis of the figure , what is the gene frequency of this mutation. I know the answer but I would be grateful if someone could please explain it. Thanks
q: number of alleles
q^2: number of people in that group suffering from that disease (frequency of the population suffering from the disease)

so when they say "prevalence of a disease is 1/2500" it means q^2 when 1 out of 2500 people will be suffering from that disease.

In short q^2=(1/2500) so q=(1/50) so 2pq=(1/25)
Means:
genotypic prevalence of the disease = q^2 = 1 out of every 2500
allelic frequency = q = 1 out of every 50
carrier frequency = 2pq = 1 out of every 25

Coming to X linked recessive disease in males:
You cannot apply the whole hw equation to males suffering from X-linked recessive diseases in question because such males have only one affected gene in one chromosome so their allelic frequency becomes equal to genotypic frequency of affected males

q = affected number of males = (1/3000)

but you can apply the hw equation to females with X linked recessive disease as they have 2 copies of the gene in two chromosome, so you got your q(frequency of allele) from the male, now calculate genotypic frequency of affected females (q^2) = (1/9000000)

I hope by gene frequency you meant genotypic frequency but if you meant allelic frequency then its basically q= (1/3000)

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#3
05-10-2015
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Quote:
 Originally Posted by CleverFOX q: number of alleles q^2: number of people in that group suffering from that disease (frequency of the population suffering from the disease) so when they say "prevalence of a disease is 1/2500" it means q^2 when 1 out of 2500 people will be suffering from that disease. In short q^2=(1/2500) so q=(1/50) so 2pq=(1/25) Means: genotypic prevalence of the disease = q^2 = 1 out of every 2500 allelic frequency = q = 1 out of every 50 carrier frequency = 2pq = 1 out of every 25 Coming to X linked recessive disease in males: You cannot apply the whole hw equation to males suffering from X-linked recessive diseases in question because such males have only one affected gene in one chromosome so their allelic frequency becomes equal to genotypic frequency of affected males q = affected number of males = (1/3000) but you can apply the hw equation to females with X linked recessive disease as they have 2 copies of the gene in two chromosome, so you got your q(frequency of allele) from the male, now calculate genotypic frequency of affected females (q^2) = (1/9000000) I hope by gene frequency you meant genotypic frequency but if you meant allelic frequency then its basically q= (1/3000)
Thank You

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