Two dihybrid pea plants (both tall and with purple flowers) are mated. The cross resulted in 9866 progeny, of which 5550 were tall with purple flowers. What are the expected ratios of the other phenotypic classes

Explanation:

A dihybrid cross is in which two genes of two different traits are crossed

As given, two dihybrid pea plants (tall with purple flower) are mated, resulting 5550 out of 9866 were tall with purple.

T= tall  

t= short,

P= purple,

p= white;

So genotype of parents are TtPp ; T is dominant over t, P is dominant over p.

Crossing between two parens=  TtPp ×  TtPp

so gamets are  = parent 1: TP, Tp, tP, tp and parent 2: TP, Tp, tP, tp

Hence the four different gametes formed.

Now arrange the gametes on the top and left side of a Punnett square it'll genotypically results into different combinations, by which phenotypic ratios can be calculated.

offspring are = TTPP, TTPp, TtPP, TtPpTTpp, TtppttPP, ttPpttpp

(T_P_)= Tall with purple flower,

(T_pp)= tall with white  flower,

(ttP_)= short with purple  flower,

(ttpp)= short with white  flower.

so it show  12:3:3:1 ratio'

Phenotypic classes are:

616 Short with white flower

1850 Tall with white flower

1850 Short with purple flower