Practice question

Complementation analysis distinguishes whether recessive mutations causing same phenotype affect same functional unit or different transcriptional units. Two homozygous mutants crossed or heterokaryon formed produce trans heterozygote carrying one mutant allele from each parent on homologous chromosomes. If each genome supplies wild-type product compensating other's defect, wild-type phenotype restored indicating mutations complement and reside in different genes. Failure to restore indicates both lesions disrupt same cistron with no intact copy available, grouping mutants into single complementation group representing one gene.