Two alleles determine flower colour in plant Datura: P determines purple; and p, white. The P locus is on smallest chromosome, number 3. In the plants trisomic for this chromosome, n + 1 pollen is never functional, and only half the n + 1 eggs are functional. Suppose that P is always completely dominant to any number of p's, and that the locus is close to centromere. What is the expected ratio of purple: white in progeny of following crosses?