Cystic fibrosis is a genetic disease of humans caused by homozygosity for a recessive gene (aa)?
Thursday, July 29th, 2010 at
1:38 am
miss a asked:
Cystic fibrosis is a genetic disease of humans caused by homozygosity for a recessive gene (aa). In a particular large population, the frequency of newborns affected wth cystic fibrosis is 1 in 3,600. In this population, what proportion of marriages between genetically unrelated normal individuals is at risk of producing a child affected with cystic fibrosis? Is it:
1 family in 30
1 family in 300
1 family in 36
1 family in 900
1 family in 15
Tagged with: Population • Proportion • Recessive Gene
Filed under: Cystic Fibrosis
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In large popuation (Hardy Weinberg equillibrium):
p^2 + 2pq + q^2 = 1; and p + q = 1
where:
p^2 = freq. of dominant homozygous (AA)
2pq = freq. of heterozygous (Aa)
q^2 = freq. of recessive homozygous (aa)
From the data:
q^2(aa) = 1/3600 = 0.00028
q(a) = SQRT 0.00028 = 0.017
p(A) = 1 – 0.017 = 0.983
2pq(Aa) = 2 x 0.983 x 0.017 = 0.0328
With this frequency of heterozygous normal (Aa) couple in the population, they may produce an affected chlid 1 in 30*).
*) 1/0.0328 = 30,48