Practice question

Parental genotype determination relies on making tester parent genetically uniform recessive so offspring phenotype directly reflects alleles contributed by parent with unknown genotype. In test cross AA x aa all progeny dominant, Aa x aa yields 1:1 dominant to recessive. Self cross or ordinary backcross AA x Aa confounds allele contributions from both parents because both can supply dominant allele, preventing clear deduction. By eliminating dominance masking through exclusive recessive contribution from tester, segregation ratio becomes unambiguous readout of gamete types produced by heterozygous parent, enabling precise genotype inference.