AP BIO Question!!!?

Question

Use the rules of probability to determine the expected ratio of offspring showing two recessive traits in the trihybrid cross (PpYyRr x Ppyyrr).

Answer 1

Trait can be considered singly.
Yy x yy & Rr x rr both are back crosses not hybrid crosses so they show a 1:1 ratio.
1/2 are Yy:1/2 are yy also 1/2 are Rr:1/2 are rr

Only Pp x Pp shows the 3:1 ratio
3/4 are P_: 1/4 are pp

Chances of getting ppyyrr are 1/4 x 1/2 x 1/2 = 1/16

Chances for P_YyRr are 3/4 x 1/2 x 1/2 = 3/16

P_yyrr chances are 3/4 x 1/2 x 1/2 = 3/16

ppYyrr chances are 1/4 x 1/2 x 1/2 = 1/16