NEET Solved Paper 2016 Question 29
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
Options:
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
Show Answer
Answer:
Correct Answer: A
Solution:
- In garden peas, the trait for tall plants (T) is dominant over the trait for dwarf plants (t). When a tall true breeding plant (TT) is crossed with a dwarf true breeding plant (tt), all the F1 generation plants will be heterozygous (Tt) and exhibit the tall phenotype because the tall allele (T) is dominant.
When these F1 plants (Tt) are selfed (Tt x Tt), the resulting genotypes of the F2 generation can be determined using a Punnett square:
T t
----------------
T | TT | Tt |
----------------
t | Tt | tt |
----------------
From the Punnett square, we can see the genotypic ratio of the F2 generation:
- 1 TT (tall homozygous)
- 2 Tt (tall heterozygous)
- 1 tt (dwarf)
So, the genotypic ratio is 1:2:1, which corresponds to:
- 1 Tall homozygous (TT)
- 2 Tall heterozygous (Tt)
- 1 Dwarf (tt)
BETA
