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In Japanese four o'clock plants, the red (R) color is incompletely dominant over white (r) flowers, and the heterozygous condition (Rr) results in plants with pink flowers.

Construct a Punnett square and give the genotypic and phenotypic ratios of the offspring for the following scenario:

You are crossing a heterozygous plant with a homozygous dominant red plant.

Hint: The first parent genotype (Rr) needs to go down the left side of the Punnett square, and the second parent genotype (RR) needs to go across the top of the Punnett square.

Genotypic and Phenotypic Ratios for Japanese Four O'clocks

[tex]\[
\begin{array}{|c|c|c|}
\hline
& R & R \\
\hline
R & RR & RR \\
\hline
r & Rr & Rr \\
\hline
\end{array}
\][/tex]

Genotypic Ratio:
- 50% RR
- 50% Rr

Phenotypic Ratio:
- 100% Red

Sagot :

GinnyAnswer
To solve this genetic cross for Japanese four o'clock plants, we'll start by constructing a Punnett square for the given genotypes. Here's the detailed step-by-step solution:

### Parent Genotypes
- Parent 1 (heterozygous): Rr
- Parent 2 (homozygous dominant): RR

### Step 1: Write the alleles from each parent
- Parent 1's alleles (Rr): These will go on the left side of the Punnett square.
- Parent 2's alleles (RR): These will go on the top of the Punnett square.

### Step 2: Construct the Punnett Square

Here is the Punnett square:

[tex]\[ \begin{array}{c|c|c} & R & R \\ \hline R & RR & RR \\ \hline r & Rr & Rr \\ \end{array} \][/tex]

### Step 3: Determine the genotypes of the offspring
From the Punnett square, we observe the following genotypes:
- 2 squares of RR
- 2 squares of Rr

### Step 4: Count the genotypes

[tex]\[ \text{Genotype counts:} \begin{aligned} &RR : 2 \\ &Rr : 2 \\ &rr : 0 \\ \end{aligned} \][/tex]

### Step 5: Calculate the genotypic ratio
The total number of possible offspring is 4 (2 + 2 + 0). Therefore, the genotypic ratio is:

[tex]\[ \begin{aligned} &RR: \frac{2}{4} = \frac{1}{2} = 50\% \\ &Rr: \frac{2}{4} = \frac{1}{2} = 50\% \\ &rr: \frac{0}{4} = 0\% \\ \end{aligned} \][/tex]

### Step 6: Determine the phenotypes and their ratios
- RR: Plants with red flowers (Red).
- Rr: Plants with pink flowers (Pink).
- rr: Plants with white flowers (White).

Given the counts from the Punnett square:
- 2 RR: Red flowers
- 2 Rr: Pink flowers
- 0 rr: White flowers

[tex]\[ \text{Phenotype counts:} \begin{aligned} &\text{Red} : 2 \\ &\text{Pink} : 2 \\ &\text{White} : 0 \\ \end{aligned} \][/tex]

### Step 7: Calculate the phenotypic ratio
The total number of offspring is 4. Therefore, the phenotypic ratio is:

[tex]\[ \begin{aligned} &\text{Red}: \frac{2}{4} = \frac{1}{2} = 50\% \\ &\text{Pink}: \frac{2}{4} = \frac{1}{2} = 50\% \\ &\text{White}: \frac{0}{4} = 0\% \\ \end{aligned} \][/tex]

### Summary
#### Genotypic Ratio:
- RR: 50%
- Rr: 50%
- rr: 0%

#### Phenotypic Ratio:
- Red: 50%
- Pink: 50%
- White: 0%

This concludes our solution, showing that when crossing a heterozygous plant (Rr) with a homozygous dominant plant (RR), the offspring will be 50% red-flowered (RR) and 50% pink-flowered (Rr), with no white-flowered (rr) plants.
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