A pea plant is heterozygous for a character and recessive homozygous for another character. Both these characters are located on different chromosomes . Another pea plant of the same species is heterozygous for both the characters. If these plants are crossed , what proportion of their offsprings will be heterozygous only for one character ?

Options

A. `25%`
B. `50%`
C. `75%`
D. `100%`

Answer

To solve the problem, we need to analyze the genetic makeup of the two pea plants involved in the cross and determine the proportion of offspring that will be heterozygous for only one character.

### Step-by-Step Solution:

1. **Identify the Genotypes of the Parent Plants:**
- The first pea plant is heterozygous for one character and homozygous recessive for another. Let's denote:
- Round seed shape (R) is dominant over wrinkled seed shape (r).
- Yellow seed color (Y) is dominant over green seed color (y).
- Therefore, the genotype of the first plant can be represented as **Rr yy** (heterozygous for seed shape and homozygous recessive for seed color).

- The second pea plant is heterozygous for both characters, so its genotype is **Rr Yy**.

2. **Determine the Gametes Produced by Each Parent:**
- The first plant (Rr yy) can produce two types of gametes:
- R y (from Rr and yy)
- r y (from Rr and yy)
- The second plant (Rr Yy) can produce four types of gametes:
- R Y
- R y
- r Y
- r y

3. **Set Up the Punnett Square:**
- We can set up a Punnett square to visualize the combinations of these gametes. The gametes from the first plant will be on one axis, and the gametes from the second plant will be on the other axis.

| | R Y | R y | r Y | r y |
|-------|-----|-----|-----|-----|
| R y | RrY | Rry | rrY | rry |
| r y | RrY | Rry | rrY | rry |

4. **Analyze the Offspring Genotypes:**
- From the Punnett square, we can identify the genotypes of the offspring:
- RrY (heterozygous for shape, heterozygous for color)
- Rry (heterozygous for shape, homozygous recessive for color)
- rrY (homozygous recessive for shape, heterozygous for color)
- rry (homozygous recessive for both traits)

5. **Count the Proportions:**
- We need to find the offspring that are heterozygous for only one character:
- Rry (heterozygous for shape, homozygous for color) - 2 occurrences
- rrY (homozygous for shape, heterozygous for color) - 2 occurrences
- Total offspring = 8
- Offspring that are heterozygous for only one character = 4 (2 Rry + 2 rrY)

6. **Calculate the Proportion:**
- The proportion of offspring that are heterozygous for only one character is:
\[ \text{Proportion} = \frac{\text{Number of heterozygous for one character}}{\text{Total offspring}} = \frac{4}{8} = \frac{1}{2} \text{ or } 50\% \]

### Final Answer:
The proportion of their offspring that will be heterozygous only for one character is **50%**.

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