## Here are some data about CF and wo RFPL markers.

 MET D7S8

MET: cf allele (diseased) is associated with the upper, purple band. Wild-type cf +allele is associated with lower, green band.
D7S8: cf allele (diseased) is associated with the lower, purple band. Wild-type cf +allele is associated with upper, green band.

 MET D7S8

Create a genetic map of cf and the RFLP markers MET and D7S8.

There are two possible ways to diagram this linkage:

How can we determine which map is correct?

Comparing MET and D7S8 inheritance

Therefore, only this map can be correct:

You are the genetic counselor, what do you tell these parents when considering the probability of child #6 having CF?

It looks like child #6 is homozygous cf since it is homozygous for the band that is linked to the cf allele. However, there is a 6% chance that recombination occurred in either parent, so you cannot simply say that you are 94% sure the child will have CF. If one parent OR the other had recombination between the CF locus and the D7S8 locus, then the child will be a healthy carrier.

One way to look at this is what is the probability the child WILL have CF: 0.94 (no recombination) X (and) 0.94 (no recombination) = 0.8836.

Alternatively, you could ask what is the chance the child WILL NOT have CF. If one parent does have recombination AND the other does not (0.94 X 0.06) OR recombination happens in the other parent (0.94 X 0.06) OR it happens in both parents (0.06 X 0.06) = 0.0564 + (or) 0.0564 + 0.0036 = 0.1164 or 11.64 % chance the child WILL NOT have CF.

## Different scenario

You are the genetic counselor, what do you tell these parents when considering the probability of child #6 having CF?

RFLP analysis using D7S8