Practice question

When point mutation lies within deleted segment deletion chromosome lacks wild-type counterpart so heterozygote deletion/mutant expresses solely mutant allele producing recessive phenotype because only defective copy present. Segregation yields half progeny receiving deletion plus mutant allele showing mutant trait and half receiving wild-type homologue showing wild phenotype. If mutation lies outside deletion deletion chromosome still carries wild copy so all offspring wild type. Observing mutant phenotype in approximately half progeny therefore indicates gene resides inside deletion interval diagnostic for physical mapping.