Practice question

Complementation succeeds when mutations reside in different genes each parental chromosome supplying wild-type allele for locus mutated in other parent. Genotype a+ b / a b+ contains one functional copy of gene A from first parent and one functional copy of gene B from second restoring both enzymatic activities required for pathway. Resulting phenotype wild-type demonstrates loci complement defining separate cistrons. Pairwise testing across mutant collection clusters complementing mutants into different groups enabling calculation of number of genes involved in trait and elucidating genetic architecture of developmental pathway.