Question

When testing for linkage between a disease gene and an RFLP marker, a LOD score of 3 for r = 0.2 indicates that

Select one:

a. the marker is within the disease gene

b. the marker is significantly linked to the disease gene at a distance of 0.2 million base pairs

c. the marker is 1000 times more likely to be linked to the disease gene at a distance of 20 map units than unlinked

d. the marker is significantly linked to the disease gene at a distance of 20% of the chromosome

Answer 1

The answer is c.

given,

r=0.2 (here r refers to recombination frequency.)

LOD score =3 (LOD gives likeliness of linkage between two genes or a gene and marker located on the chromosome. LOD value 3 indicates that the two genes or a gene and marker are 1000 times more likely to be linked.)

using r, map units (measure of genetic distance) can be determined.

1% recombination frequency = 1 map unit.

given, r=0.2 which implies,   the percentage recombination frequency= 0.2*100

  =20%

20% recombination frequency= 20 map units.

therefore the disease gene and RFLP marker are at a distance of 20 map units and 1000 times more linked than the unlinked.