Introduction: genes at different locations, non allelic, genes in same region, complementation test to see if one mutant can complement another. Blocks at either step result in white rather than wild type purple: aabb or aabb depending which is mutant if these strains are crossed = aabb = purple flower. = complementation together each strain provides what the other is lacking (a, b) = non-allelic mutations = mutations in different genes. If we get a third white flower fro(cid:373) (cid:271)reedi(cid:374)g, we wo(cid:374)"t k(cid:374)ow if it is (cid:373)uta(cid:374)t i(cid:374) gene a or gene b or some other gene: use complementation by crossing two homozygous individuals with similar mutant phenotypes. If all progeny are wild type, then each parents most likely has a mutation in a different gene: non allelic mutations = different gene locus, complement each other. Note: mutations used in complementation tests are usually true breeding (homozygous at mutant locus) and recessive mutations.