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

Options

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

Answer

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

### Step-by-Step Solution:

1. **Identify the Alleles**:
- For plant height, let’s denote the alleles as:
- Capital T (T) = tallness (dominant)
- Small t (t) = shortness (recessive)
- For flower color, we denote:
- Capital C (C) = color (dominant)
- Small c (c) = color (recessive)

2. **Determine the Parental Genotypes**:
- In a dihybrid cross, the parents are typically heterozygous for both traits. Therefore, the parental genotypes will be:
- Parent 1: TtCc
- Parent 2: TtCc

3. **Gamete Formation**:
- Each parent can produce four types of gametes due to independent assortment:
- Parent 1 gametes: TC, Tc, tC, tc
- Parent 2 gametes: TC, Tc, tC, tc

4. **Construct a Punnett Square**:
- Create a 4x4 Punnett square to determine the offspring genotypes by crossing the gametes from both parents.

5. **Fill in the Punnett Square**:
- The combinations will yield the following genotypes:
- TTCC, TTCc, TtCC, TtCc
- TTcc, Ttcc, ttCC, ttCc
- TtCc, Ttcc, ttCc, ttcc
- (Continue filling in all combinations)

6. **Count the Offspring Genotypes**:
- After filling in the Punnett square, count the total number of offspring genotypes that exhibit the heterozygous condition for tallness (Tt).
- The genotypes that are heterozygous for tallness (Tt) will be:
- TtCC, TtCc (from the first two rows)
- TtCc (from the third row)
- Count these occurrences.

7. **Calculate the Percentage**:
- Total offspring = 16 (4x4 Punnett square)
- Count of Tt genotypes = 8
- Percentage of heterozygous tallness = (Number of Tt genotypes / Total Offspring) × 100
- Calculation: (8 / 16) × 100 = 50%

### Final Answer:
**50% of the zygotes contain a heterozygous condition for tallness.**

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