Generating a segregating population for fine mapping

A modern gene hunt often begins with a cross between parents with contrasting traits. In the example shown, Parent 1 carries the wild-type allele (D) and is normal, while Parent 2 carries the mutant allele (d) and as a result has a disease. All Fļ progeny are heterozygous at all loci and are normal. F2 progeny are segregating for the disease. Most progeny with the disease have the Parent 2 genotype (Parental mutant). Rare mutant individuals have experienced a recombination event in one of the parents in the chromosomal interval between markers M1 and M2 (heterozygous mutant, bottom right).