6.
One person in 10,000 has PKU which is a potentially lethal, recessive disorder.
These individuals lack an enzyme that allows the digestion of the
amino acid phenylalanine and must be careful not have this amino acid in
their diet. What are the chances that someone is a carrier, their
spouse is a carrier and then their child being a PKU victim?
A. 1 person with PKU/10,000 total = 0.0001
q2 = 0.0001, therefore the recessive
allelic frequency is q = 0.01
B. p + q = 1
p = 1 - 0.09
p = 0.99 - dominant allelic frequency
C.
| Genotype |
Designation |
Frequency |
Percent |
| Homozygous Dominant |
pp or p2 |
(0.99)2 = 0.98 |
98% |
| Heterozygote |
pq |
2(0.99)(0.01) = 0.0198 |
1.98% |
| Homozygous Recessive |
qq |
(0.01)2 = 0.0001 |
0.01% |
The chances of a random married
couple both being carriers is 0.0198 x 0.0198 = 0.00039 or 0.039%.
Since the chance that two heterozygotes will produce a homozygous recessive
is 0.25, the chance that this couple will have a PKU baby is 0.000098 or
0.0098%.
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