Assinment

1.. A certain large population is found to exhibit a frequency of 3% for an autosomal recessive trait, i.e. 3 people out of 100, on average, have the trait (assume 100% penetrance). Assuming the alleles are in Hardy-Weinberg equilibrium, calculate the expected carrier frequency. When actually tested, it was found that the carrier frequency was 15%. Suggest one possible explanation for this non-equilibrium value.

2. a. A biallelic locus, Aa, has allele frequencies of A = 80% and a=20% in a certain population. Another biallelic locus, Bb, has allele frequencies of B = 90% and b = 10% in the same population. Both loci are found to be in Hardy-Weinberg equilibrium. Calculate the expected percentages of each of the AA, Aa, aa, BB, Bb, and bb genotypes in the population.

AA=                 ; Aa=                  ; aa=                 ;BB=                 ; Bb=                  ; bb=                 ;

b. A recessive digenic disorder (100% penetrant) occurs ONLY when one has the aabb genotype. It’s found that 15 people out of 10,000 in this population have the disorder. What would be the expected frequency of the disorder if the Aa locus and the Bb locus were segregating independently? Is the actual frequency significantly different from this?

3. A very rare disorder is shown to depend on the genotype at three unlinked autosomal loci, A/a, B/b and C/c and that to be affected one must be homozygous for the rare allele at all three loci, that is, aabbcc. The MZ twin disorder concordance is 100%, implying that the penetrance is 100%. Calculate the expected dizygotic twin concordance for presence of the affected trait, that is, if one DZ twin shows the trait, what is the chance that the 2nd twin will be affected? (Hint: because the trait is rare, assume that both parents are heterozygous for all three loci. This is NOT the probability that both twins are affected among all DZ twin pairs.)