Consider a test cross between a homozygous recessive yellow seeded plant with a plant having an unknown seed. 50% of the offsprings in F1 generation have yellow seeds and 50% have green seeds.
Which of the following statements is/are TRUE about the cross?
1: The unknown seed is homozygous recessive for green.
2: The unknown seed is heterozygous for green.
3: All the offsprings in F2 generation will have green seeds.
4: All the offsprings in F2 generation will have yellow seeds.

Options

A. only 1
B. only 2
C. only 1 and 4
D. only 2 and 3

Answer

To solve the question, we will analyze the test cross between a homozygous recessive yellow seeded plant and a plant with an unknown genotype. We know that 50% of the offspring in the F1 generation have yellow seeds and 50% have green seeds.

### Step-by-Step Solution:

1. **Identify the Genotype of the Homozygous Recessive Parent:**
- The homozygous recessive yellow seeded plant has the genotype **yy** (where 'y' represents the allele for yellow seeds).

2. **Determine the Possible Genotype of the Unknown Seed:**
- Since we have a test cross, we are crossing the unknown seed with the homozygous recessive yellow seeded plant (yy).
- The offspring show a 1:1 ratio of yellow to green seeds. This indicates that the unknown seed must carry one dominant allele for green seeds (Y) and one recessive allele for yellow seeds (y). Thus, the unknown seed must be **Yy** (heterozygous for green).

3. **Analyze the F1 Generation:**
- When the unknown seed (Yy) is crossed with the homozygous recessive yellow seeded plant (yy), the possible genotypes of the F1 offspring are:
- From Yy (unknown seed): Y (dominant) or y (recessive)
- From yy (homozygous recessive): y (only)
- The resulting offspring will be:
- 50% Yy (green seeds)
- 50% yy (yellow seeds)

4. **Determine the F2 Generation:**
- If we self-cross the F1 generation (Yy x Yy), the genotypes of the F2 generation will be:
- YY (homozygous dominant) - green seeds
- Yy (heterozygous) - green seeds
- yy (homozygous recessive) - yellow seeds
- The phenotypic ratio in the F2 generation will be 3 green seeds (YY and Yy) to 1 yellow seed (yy).

5. **Evaluate the Statements:**
- **Statement 1:** The unknown seed is homozygous recessive for green. (False)
- **Statement 2:** The unknown seed is heterozygous for green. (True)
- **Statement 3:** All the offspring in F2 generation will have green seeds. (False)
- **Statement 4:** All the offspring in F2 generation will have yellow seeds. (False)

### Conclusion:
The only true statement is **Statement 2**: The unknown seed is heterozygous for green.

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