Practice question

Rice awn character controlled by two loci where dominant allele at either locus promotes awn elongation via transcription factors activating cell elongation in parallel pathways. Biochemically either gene product suffices to trigger development. Cross heterozygous at both loci selfed produces 15 awned grains comprising 9 A-B- +3 A-bb +3 aaB-, and 1 awnless aabb, demonstrating diagnostic 15:1 duplicate dominant epistasis. This redundancy reflects selection during domestication where loss of one gene compensated by other. Pattern contrasts with squash dominant masking, sweet pea complementary both required, mouse recessive epistasis examples.