When a breed of cattle with red coats is crossed with the same breed with coats, the offspring all have coats with a mixture of red and white hairs, a condition called roan. If roan cows were crossed with a red- coated bull, the theoretical ratio of the offspring would be
let red coat be RR (dominant) & white coat be rr (recessive).
in F1 generation :- RR× rr = Rr (roan)
in F2 generation :- when roan (Rr) is mated with red (RR)
Rr × RR
therefore the ratio will be - RR : Rr (Red : roan) = 1:1