A genetic model suggests that 80% of the plants grown from a cross between two given strains

Question:

A genetic model suggests that 80% of the plants grown from a cross between two given strains of seeds will be of the dwarf variety. After breeding 200 of these plants, 136 were observed to be of the dwarf variety.
(a) Does this observation strongly contradict the genetic model?
(b) Construct a 95% confidence interval for the true proportion of dwarf plants obtained from the given cross.