Practice question

Complementation test depends on ability of wild-type allele to mask recessive defect by providing functional product in heterozygote. Dominant mutations express phenotype even with single copy so trans configuration containing dominant allele plus wild homologue still shows mutant trait regardless of second mutation location preventing discrimination between allelic and non-allelic lesions. Dominance masks capacity for complementation causing universal failure pattern and uninterpretable results. Therefore test restricted to recessive loss-of-function alleles where wild allele can supply normal function if separate locus, excluding dominant traits from functional analysis applicability.