12 colorless : 3 purple : 1 red
Work Step by Step
Note this is a dihybrid cross. The dihybrid cross between the heterozygous parents is attached. The dominant allele I inhibits color. That means that a cross with either "II," "Ii," or "iI" will inhibit color and the maize will be colorless. There are 12 of these total. The 4 remaining plants are "ii," meaning their color is not inhibited. Now examining the P and p alleles, we see that the dominant P allele causes purple color. Thus, anything in the form "iiPP," "iiPp," or "iipP" will be purple because "ii" means color is expressed and the presence of P indicates purple color. There are 3 of these expressed. The completely homozygous recessive cross "iipp," of which there is 1, has color expressed and is totally recessive so it is red. The genotypic ratio is 9:3:3:1.