How do we figure out the genotypes in a family by looking at gel electrophoresis?

if you are given a pedigree with the results of gel electrophoresis such as the bands visible on the gel how would you read the gel and figure out the genotypes (whether the individual is heterozyous or homozygous for mutant or wildtype allele) of the individuals. please explain but an example would also be helpful and/or provide sources for additional help.How do we figure out the genotypes in a family by looking at gel electrophoresis?
Scientists use something called Restriction Fragment Length Polymorphism or RFLP. It's pretty complicated and lengthy to explain, but I'll direct you to the wiki entry