In Mirabilis jalapa, RR, Rr and rr determine red , pink and white colours respectively. When `F_(1)` hybrid of RR and r was crossed with dominant parent, the ratio produced in

Options

A. All red
B. 2 red : 2 Pink
C. All white
D. 2Pink : 2 white.

Answer

To solve the problem regarding the inheritance of flower color in Mirabilis jalapa, we will follow these steps:

### Step 1: Understand the Genotypes and Phenotypes
In Mirabilis jalapa:
- The genotype **RR** produces red flowers.
- The genotype **Rr** also produces red flowers due to the presence of the dominant allele R.
- The genotype **rr** produces white flowers.

### Step 2: Determine the F1 Generation
When we cross the dominant parent **RR** (red) with the recessive parent **rr** (white), the F1 generation will all be **Rr** (red) due to the dominance of the R allele over the r allele. Therefore, all offspring in the F1 generation will have red flowers.

### Step 3: Cross the F1 Generation with the Dominant Parent
Now, we need to cross the F1 hybrid **Rr** (red) with the dominant parent **RR** (red):
- The possible gametes from **Rr** are R and r.
- The possible gametes from **RR** are R and R.

### Step 4: Create a Punnett Square
We can set up a Punnett square to visualize the cross:

| | R (from RR) | R (from RR) |
|-------|--------------|--------------|
| **R** | RR | RR |
| **r** | Rr | Rr |

### Step 5: Analyze the Offspring
From the Punnett square, we can see the following genotypes of the offspring:
- 2 RR (red)
- 2 Rr (red)

### Step 6: Determine the Phenotypic Ratio
All offspring will display the red phenotype since both RR and Rr result in red flowers. Therefore, the ratio of red to white flowers is:
- 2 red (RR) + 2 red (Rr) = 4 red
- 0 white (rr)

Thus, the ratio of red to white flowers is **4:0** or simply all red.

### Conclusion
The answer to the question is that when the F1 hybrid of RR and rr is crossed with the dominant parent (RR), the resulting phenotypic ratio is **all red flowers**.

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