Question

In a hybridization experiment, out of 300 plants produced in the $F_1$ generation, 225 plants produced green colour pods while the rest produced yellow colour pods.
Determine the number of pea plants which are not true breeding for the dominant trait in the $F_1$ generation.

• A. 100
• B. 50
• C. 75
• D. 150

Answer 1

The correct option is D 150

Let the alleles responsible for the green and yellow coloration of pods be G and g respectively (As green pod colour is dominant over yellow).

Given that out of 300 plants in $F_1$ generation,
225 plants are green pod producing plants.

Hence the number of yellow pod producing plants
= 300 - 225 = 75.

Hence plants producing green pods : plants producing yellow pods = 225 : 75 = 3 : 1

Since 25% of $F_1$ offspring are recessive, hence both the parents have a recessive allele. Hence, the possible genotype: _g x _g.

Now, since 75% of the $F_1$ offspring produce green pods, hence, the genotype of the parent plants is Gg x Gg.


Genotypic ratio in the $F_1$generation:
GG : Gg : gg = 1 : 2 : 1
$\Rightarrow$ Out of 4 plants, number of plants not true breeding for green pods = 2 (Gg)
$\Rightarrow$ Out of 300 plants, number of plants not true breeding for green pods = 150.

Since, production of green pods is a dominant trait, hence, the number of pea plants not true breeding for the dominant trait = 150.