The hemophilia gene is located 12 map units from the red-green colorblindness gene on the X chromosome. Red-green colorblindness is recessive to normal colorvision. A woman with normal blood clotting and normal color vision, but whose father was a hemophiliac and whose mother was red-green colorblind, marries a man who is not a hemophiliac and is not colorblind. What percent of their children will be colorblind and have hemophilia?
The answer was given. It is 3%. But I need to know how to get that answer.
I found some time to answer your question after all. Let's consider all of the information you have been given step by step:
First, you know that the two genes of interest are on the X chromosome, and that they are 12 map units apart from each other. Because they are on the same chromosome, they are called "linked" genes. A map of the locations of genes on the same chromosome can be constructed using the frequency of recombination between those genes during crossing over events in meiosis. Genes that are farther apart on the chromosome are less likely to be coinherited due to switching of pieces of the chromosome arms (crossover - for a review of how linkage maps are made see one of these websites: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/L/Linkage.html ...
The expert locates sex-linked traits on genes. The percent of children which will be colorblind and have hemophilia are determined.