You mean the stuff where you are given distances between loci in centimorgans (or %recombination which is I think the same thing) and told to find a way to arrange them that makes sense? Never came across a problem like that, but I think my first sentence basically explained the concept anyway. The basic principle is that every unit of physical distance along a chromosome has a fixed probability (percentage) of forming a crossover (basic assumption, not really uniformly true in real life).
