In `F_(2)` generation of a Mendelian dihybride cross (w.r.t plant height and flower colour in garden pea), _______ % of the zygote contain heterozyogus condition for tallness.

Options

A. 25
B. 50
C. 75
D. `12.5`

Answer

To solve the question regarding the percentage of zygotes containing a heterozygous condition for tallness in the F2 generation of a Mendelian dihybrid cross, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Traits**:
- In garden peas, plant height has two alleles: tall (T) which is dominant, and dwarf (t) which is recessive.
- Flower color also has two alleles: violet (W) which is dominant, and white (w) which is recessive.

2. **Setting Up the Dihybrid Cross**:
- The parental generation (P) consists of one plant that is homozygous dominant for both traits (TTWW) and another that is homozygous recessive for both traits (ttww).
- The F1 generation will all be heterozygous for both traits (TtWw).

3. **F1 Generation Cross**:
- When we cross the F1 generation (TtWw x TtWw), we need to determine the gametes produced. The possible gametes are:
- TW (tall, violet)
- Tw (tall, white)
- tW (dwarf, violet)
- tw (dwarf, white)

4. **Constructing the Punnett Square**:
- A 4x4 Punnett square is created to represent the combinations of these gametes.
- The resulting combinations will yield 16 different genotypes in the F2 generation.

5. **Identifying Heterozygous Conditions for Tallness**:
- We are interested in the heterozygous condition for tallness, which is represented by Tt.
- In the Punnett square, we will find the combinations that yield Tt:
- TtWw (tall, violet)
- Ttw (tall, white)
- Each of these combinations occurs multiple times in the 16 squares.

6. **Counting the Heterozygous Zygotes**:
- From the Punnett square, we can count the occurrences of Tt:
- There are 8 squares that represent the heterozygous condition (Tt).
- The total number of zygotes is 16.

7. **Calculating the Percentage**:
- To find the percentage of zygotes that are heterozygous for tallness, we use the formula:
\[ \text{Percentage} = \left( \frac{\text{Number of heterozygous zygotes}}{\text{Total number of zygotes}} \right) \times 100 \]
- Substituting the values:
\[ \text{Percentage} = \left( \frac{8}{16} \right) \times 100 = 50\% \]

### Final Answer:
Thus, **50%** of the zygotes in the F2 generation contain a heterozygous condition for tallness.

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