Page 151 - Applied Probability

7. Computation of Mendelian Likelihoods

1
2
a/b c/d 135

♦
3 4 5
b/d b/d b/c
FIGURE 7.7. Risk Prediction for a Recessive Disease via a Linked Marker
8. A healthy male had a sister with cystic fibrosis (CF), but she and his
parents are dead. What is his risk of being a carrier for this recessive
disease? About 75 percent of all disease alleles at the CF locus are
accounted for by the ∆F 508 mutation. If he tests negative for the
∆F 508 mutation, what is his risk of being a carrier [28]?

1 2

3 4 5 6

7 8

FIGURE 7.8. Risk Prediction for an X-linked Recessive Disease

9. The grandson 7 depicted in the pedigree of Figure 7.8 is afflicted
by a lethal, X-linked recessive disease [25]. Problem 11 of Chapter 1
notes that if the carrier females for such a disease are fully fit, then
they have a population frequency 4µ, where µ is the mutation rate to
the disease allele. In view of this fact, demonstrate that the mother
4 has a chance of approximately 5/13 of carrying the disease allele.
Consequently, her next son has a chance of 5/26 of being affected.
(Hints: Either the grandmother 1 is a carrier, or the mother 4 is a