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See pedigree drawing
(figure below). Individuals II3 and III1
have a clinical diagnosis of Duchenne
muscular dystrophy. MLPA analysis revealed
no deletion or duplication in III1. Prior to
considering point mutation analysis, your
local clinical geneticist asked you to
perform linkage analysis to determine the
carrier risk for II4 (and you agreed!).
Marker order is A, B, C, D. Marker A is
directly adjacent to the 5’ end of the gene,
marker D is directly adjacent to the 3’ end
of the gene and the markers are equally
spaced with respect to the coding sequence.
Your results are as
follows: I1 – A=1, B=3, C=4, D=2; I2 –
A=1/3, B=1/3, C=1/3, D=2/3; II2 – A=1/1,
B=1/3, C=3/4, D=2/3; II3 – A=1, B=1, C=3,
D=3; II4 – A=1/1, B=3/3, C=1/4, D=2/2; III1
– A=1, B=1, C=3, D=3.
Construct haplotypes
and calculate the carrier risk for II4.
There is approximately a 10% chance of
recombination within the gene at meiosis and
for simplicity you should assume that point
mutation positions and recombination
positions are random with respect to the
coding sequence (is this really the case?). |
