Question

Tall plant with yellow seeds (TtYy) is crossed with tall plant with green seeds (Ttyy). Find out proportions of offspring in F$_1$ generation:

• A. $\frac{3}{8}$ Tall plants with green seeds, $\frac{1}{8}$ Dwarf plants with green seeds
• B. $\frac{2}{8}$ Tall plants with green seeds, $\frac{1}{8}$ Dwarf plants with green seeds
• C. $\frac{1}{8}$ Tall plants with green seeds, $\frac{3}{8}$ Dwarf plants with green seeds
• D. $\frac{2}{8}$ Tall plants with green seeds, $\frac{2}{8}$ Dwarf plants with green seeds

Hint:

Solve Dihybrid crosses by breaking them down into two Monohybrid crosses. It is faster and less prone to error than drawing a large Punnett square (which would be $4 \times 2 = 8$ squares here).

Answer 1

The Correct Option is A

Step 1: Identify the Cross:
Parent 1: $TtYy$ (Tall, Yellow)
Parent 2: $Ttyy$ (Tall, Green)
Step 2: Analyze Traits Independently:
Assuming independent assortment:

• Height ($Tt \times Tt$):
  • Genotypes: $1 TT : 2 Tt : 1 tt$
  • Phenotypes: $\frac{3}{4}$ Tall, $\frac{1}{4}$ Dwarf
• Seed Colour ($Yy \times yy$):
  • Genotypes: $1 Yy : 1 yy$
  • Phenotypes: $\frac{1}{2}$ Yellow, $\frac{1}{2}$ Green

Step 3: Calculate Proportions for Required Phenotypes:
The question options focus on "Tall with Green seeds" and "Dwarf with Green seeds".

• Tall with Green seeds: \[ P(\text{Tall}) \times P(\text{Green}) = \frac{3}{4} \times \frac{1}{2} = \frac{3}{8} \]
• Dwarf with Green seeds: \[ P(\text{Dwarf}) \times P(\text{Green}) = \frac{1}{4} \times \frac{1}{2} = \frac{1}{8} \]

Step 4: Match with Options:
Option (A) states "$\frac{3}{8}$ Tall plants with green seeds" and "$\frac{1}{8}$ Dwarf plants with green seeds". This matches our calculation.