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#1
05-26-2011
 USMLE Forums Addict Steps History: 1+CK+CS+3 Posts: 186 Threads: 61 Thanked 259 Times in 66 Posts Reputation: 269
Hardy-weinberg and calculation of the frequency of disease?

After graduation, you and 19 friends build a raft, sail to a deserted island, and start a new population, totally isolated from the world. Two of your friends carry (that is, are heterozygous for) the recessive cf allele, which in homozygotes causes cystic fibrosis.

A. Assuming that the frequency of this allele does not change as the population grows, what will be the
instance of cystic fibrosis on your island?
B. Cystic fibrous births on the island is how many times greater than the original mainland. The frequency of
births on the mainland is .059%.

#2
05-26-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,378 Threads: 194 Thanked 3,254 Times in 881 Posts Reputation: 3264
Part a

After graduation, you and 19 friends build a raft, sail to a deserted island, and start a new population, totally isolated from the world. Two of your friends carry (that is, are heterozygous for) the recessive cf allele, which in homozygotes causes cystic fibrosis.

A. Assuming that the frequency of this allele does not change as the population grows, what will be the incidence of cystic fibrosis on your island?

A) Assuming that half of the population is female & the other half is male:

n = 20
MALE heterozygous carrier = 2/20 = 1/10
FEMALE heterozygous carrier = 2/20 = 1/10
Recessive Disease = 1/4 chance to pass the disease
INCIDENCE = 1/10*1/10*1/4 = 0.0025

You could also use the equation, but for me this way is easier

Last edited by bebix; 05-26-2011 at 06:47 PM. Reason: change instance for incidence (?)
 The above post was thanked by: Claus_CU (05-27-2011), Dr. Mexito (03-24-2012)
#3
05-26-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,378 Threads: 194 Thanked 3,254 Times in 881 Posts Reputation: 3264
Part b

Incidence = 0.0025 = 0.25%

0.25/0.059 = 0.25/0.06 = aprox. 4
 The above post was thanked by: Dr. Mexito (03-24-2012)

 Tags Genetics-, Step-1-Questions

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