The assignment of the relative positions of deletion mutations along chromosomes. In the first phase, many individuals are studies for the presence of cytogenetic markers and later phases use restriction fragment length polymorphisms to detail the chemical nature of the aberrations. Futhermore, an experimental approach for identifying the location of a point mutation by testing whether recombination with a gene with a known deletion will produce the wild-type protein, in which case the site of point mutation lies outside the deleted region, or whether it fails to produce the wild-type protein, in which case the point mutation lies within the deleted region. A sufficiently large number of deletion mutants will narrow the location of the point mutation to a single nucleotide.