A tall true breeding garden pea plant is crossed with a dwarf true breeding garden pea plant. When the F1 plants were selfed the resulting genotypes were in the ratio
Answer: (A) 1 : 2 : 1 :: Tall homozygous : Tall heterozygous : Dwarf. Answer: (A) 1 : 2 : 1 :: Tall homozygous : Tall heterozygous : Dwarf Solution: Crossing true-breeding tall (TT) with true-breeding dwarf (tt) gives an all-tall Tt F1.
- A.1 : 2 : 1 :: Tall homozygous : Tall heterozygous : Dwarf✓
- B.1 : 2 : 1 :: Tall heterozygous : Tall homozygous : Dwarf
- C.3 : 1 :: Tall : Dwarf
- D.3 : 1 :: Dwarf : Tall
Correct Answer
(A) 1 : 2 : 1 :: Tall homozygous : Tall heterozygous : Dwarf
Solution & Explanation
Answer: (A) 1 : 2 : 1 :: Tall homozygous : Tall heterozygous : Dwarf Solution: Crossing true-breeding tall (TT) with true-breeding dwarf (tt) gives an all-tall Tt F1. Selfing Tt gives genotypes TT : Tt : tt in the ratio 1 : 2 : 1, i.e., tall homozygous : tall heterozygous : dwarf. (The phenotypic ratio is 3 tall : 1 dwarf, but the question asks for genotypes.) NCERT Reference: NCERT Class XII, Ch 4, p.58, lines 15-17: "This leads to a phenotypic ratio of 3/4th tall : (1/4 TT + 1/2 Tt) and 1/4th tt, i.e., a 3:1 ratio, but a genotypic ratio of 1:2:1."