Question

Ratio between parental types and recombinants in a typical dihybrid cross conducted by Mendel is ___.

• A. 6:10
• B. 5:3
• C. 3:1
• D. 1:1

Answer 1

The correct option is B

5:3

In a cross involving different seed shape alleles (round, R, and wrinkled, r) and different seed color alleles (yellow, Y, and green, y), four types of gametes are expected: RY, Ry, rY, and ry. Therefore, in the $F_2$ generation there are 16 possible combinations of alleles, each of them equally probable. The $F_2$ progeny of dihybrid cross exhibit 4 different phenotypes. Yellow round (9) and green wrinkled (1) are parental combinations. Yellow wrinkled (3) and green round (3) are recombinants. Thus, the ratio becomes (9+1):(3+3) = 10:6, which when simplified is 5:3.