Question

Arrange the following in decreasing order based on the results obtained in the $F_2$ progeny of a dihybrid cross.
(A) Total number of parental genotypes
(B) Total number of recombinant genotypes
(C) Total phenotypes
(D) Total genotypes

• A. C, B, D, A
• B. A, C, D, B
• C. D, A, C, B
• D. D, B, C, A

Answer 1

Answer: (D)

D, B, C, A

A dihybrid cross between two pure varieties that differ in two pairs of contrasting characters (for example, TTRR, tall plants with red flowers x ttrr dwarf plants with white flowers) obtains $F_1$ generation (TtRr, tall plants with red flowers). A dihybrid cross between two hybrids (TtRr) give the phenotypic ratio of 9 (tall plants with red flowers) : 3 (tall plants with white flowers): 3 (dwarf plants with red flowers):1 (dwarf plants with white flowers). Therefore, total number of phenotypes in $F_2$ generation is 4 (C). The genotypic ratio for $F_2$ generation is 1 TTRR: 2 TTRr :1 TTrr: 4 TtRr: 2 TtRR : 2 Ttrr:1 ttRR: 2 ttRr : 1ttrr (total genotypes= 9, D). Total parental genotypes (TTRR and ttrr) in $F_2$ generation are 2 (A) and total recombinant genotype are 7 (B).
Therefore, the correct answer is option D.