Question

A tall true breeding garden pea plant is crossed with a dwarf true breeding garden pea plant. When the $F_1$ plants were selfed the resulting genotypes were in the ratio of

• 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

Answer 1

Answer: (A)

A cross between pure breeding tall (TT) and dwarf (tt) plants produce all tall (Tt) plants in $F_1$ progeny. These heterozygous tall plants produce 50% gametes with "T" allele and 50% with "t" allele. Random fusion of these gametes from two heterozygous tall plants gives tall and dwarf plants in 3:1 ratio. out of 3/4 tall plants; 1/4 are homozygous tall (TT) and 2/4 are heterozygous tall (Tt). This makes the genotypic ratio for $F_2$ generation as 1 homozygous tall (TT): 2 heterozygous tall (Tt): 1 homozygous dwarf (tt). This makes option B incorrect and option A correct. Option D is incorrect as 3/4 plants are tall while 1/4 are the dwarf in $F_2$ generation. Option C is incorrect as the question is asking the genotypic ratio. The correct answer is A.