A true breeding plant producing red flowers is crossed with a pure plant producing white flowers. Allele for red colour of flower is dominant. After selfing the plants of first filial generation, the proportion of plants producing white flowers in the progeny would be

Options

A. `3//4 `
B. `1//4`
C. `1//3`
D. `1//2`

Answer

To solve the problem, we will follow these steps:

### Step 1: Identify the Genotypes of the Parent Plants
- The true breeding plant producing red flowers is homozygous for the red flower allele, which we denote as **RR** (capital R for red).
- The pure plant producing white flowers is homozygous for the white flower allele, denoted as **rr** (small r for white).

### Step 2: Perform the Cross Between Parent Plants
- When we cross the two parent plants (RR x rr), the gametes from the red flower parent will all be **R**, and the gametes from the white flower parent will all be **r**.
- The resulting genotype of the first filial generation (F1) will be **Rr** (heterozygous).

### Step 3: Determine the Phenotype of the F1 Generation
- Since the allele for red flowers (R) is dominant over the allele for white flowers (r), all plants in the F1 generation will exhibit the red flower phenotype.

### Step 4: Selfing the F1 Generation
- Now, we will self the F1 plants (Rr x Rr). The gametes produced by each F1 plant will be **R** and **r**.
- The Punnett square for this cross will look like this:

```
R r
-------------
R | RR | Rr |
-------------
r | Rr | rr |
```

### Step 5: Analyze the Progeny Genotypes
- From the Punnett square, we can see the following genotypes:
- **1 RR** (homozygous red)
- **2 Rr** (heterozygous red)
- **1 rr** (homozygous white)

### Step 6: Determine the Phenotypic Ratio
- The phenotypes corresponding to the genotypes are:
- **RR** and **Rr** produce red flowers.
- **rr** produces white flowers.
- Therefore, the phenotypic ratio is:
- 3 red: 1 white.

### Step 7: Calculate the Proportion of White Flower Plants
- The proportion of plants producing white flowers in the progeny is:
- **1 out of 4** total plants, which simplifies to **1/4**.

### Conclusion
- The proportion of plants producing white flowers in the progeny after selfing the F1 generation is **1/4**.