The snapdragon plants that bred true for white petals were crossed with a plant that bred true for purple petals. All the F1 plants were with white petals. These F1 plants were self crossed and the results obtained in F2 were shown.
a) The ratio in F2 is approximately 12:3:1. This indicates epistasis and a double heterozygote condition. The ratio of the solid purple color was one third the rate of white. Hence, it should be formed either of E/-; e/e or d/d; E/-. The meaning that in F1 the parent is also a heterozygote, which would be represented as D/-; e/e or d/d; E/-. A cross made between them is as follows:
D/D; e/e (white) X d/d; E/E (purple)
F 1 progeny:
D/d; E/e
F 2 progeny:
9 D/-; E/- white
3 d/d; E/- purple
3 D/-; e/e white
1 d/d; e/e spotted purple
It should be noted that D blocks the expression of both E and e, while d has no effect on the expression of E and e. E results in solid purple and e results in spotted purple. At the same time, E blocks the expression of D or d, where D results in solid purple and d results in spotted purple.
b) If white plant is e/e the progeny would be as follows:
¼ D/d; E/e white
¼ D/d; e/e white
¼ d/d; E/e solid purple
¼ d/d; e/e spotted purple
This shows that the parents were D/d; e/e (white) X d/d; E/e (purple).