Deletion mapping is a genetic technique used to determine the approximate location of a mutation within a gene or chromosome. It is based on recombination between a strain carrying an unknown point mutation and a series of strains carrying known deletions.
Principle In deletion mapping, an organism carrying a point mutation is crossed with multiple strains, each of which carries a deletion spanning a different region of the same gene. If recombination produces wild-type offspring, the point mutation must lie outside the deleted region. A functional copy of the gene can then be reconstructed from the intact DNA contributed by the two parental strains. If no wild-type recombinants are produced, the point mutation is inferred to lie within the deleted region. Because one parent lacks that region entirely, recombination cannot restore a complete wild-type sequence.
Example
Consider a wild-type copy of gene A and a mutant allele carrying a point mutation at an unknown position. Two additional strains carry different deletions within the same gene, designated del-1 and del-2. In the figure, the point mutation lies within the region deleted in del-1. Crossing the point mutant with the del-1 strain is therefore not expected to produce wild-type recombinants: the point-mutant chromosome carries a mutation at that position, while the corresponding sequence is absent from the deletion chromosome. By contrast, the point mutation lies outside the region deleted in del-2. Recombination between the point-mutant and del-2 chromosomes can therefore produce a chromosome containing neither the point mutation nor the deletion. The recovery of wild-type recombinants indicates that the point mutation lies outside the del-2 deletion. Not every recombination event between the point mutant and del-2 will restore the wild-type allele. Only crossovers occurring at suitable positions can reconstruct an intact wild-type sequence.
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