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 will follow these steps:

### Step 1: Identify the Genotypes of the Parent Plants
1. **First Plant**: Heterozygous for one character (let's say height) and homozygous recessive for another character (let's say seed shape).
- Genotype: Tt rr (where T = tall, t = dwarf, R = round, r = wrinkled)

2. **Second Plant**: Heterozygous for both characters.
- Genotype: Tt Rr

### Step 2: Determine the Gametes Produced by Each Parent
- **First Plant (Tt rr)** can produce two types of gametes:
- T r
- t r

- **Second Plant (Tt Rr)** can produce four types of gametes:
- T R
- T r
- t R
- t r

### Step 3: Set Up a Punnett Square
We will set up a Punnett square using the gametes from both plants:

| | T R | T r | t R | t r |
|-------|-----|-----|-----|-----|
| T r | Tt Rr | Tt rr | tt Rr | tt rr |
| t r | Tt Rr | Tt rr | tt Rr | tt rr |

### Step 4: Analyze the Offspring Genotypes
From the Punnett square, we can list the offspring genotypes:
1. Tt Rr (heterozygous for both characters)
2. Tt rr (heterozygous for height, homozygous recessive for seed shape)
3. tt Rr (homozygous recessive for height, heterozygous for seed shape)
4. tt rr (homozygous recessive for both characters)

### Step 5: Count the Progeny with Heterozygosity for Only One Character
From the offspring:
- Tt rr: Heterozygous for height only (1)
- tt Rr: Heterozygous for seed shape only (1)

Total offspring with heterozygosity for only one character = 2

### Step 6: Calculate the Proportion of Such Offspring
Total offspring = 4 (Tt Rr, Tt rr, tt Rr, tt rr)
Offspring that are heterozygous for only one character = 2

Proportion = (Number of heterozygous for one character) / (Total offspring) = 2 / 4 = 1/2

### Final Answer
The proportion of their offspring that will be heterozygous only for one character is **1/2** or **50%**.

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