A horticulturist wants to produce geraniums with specific characteristics. She knows that the trait of red flowers is governed by the allele [tex]R[/tex] ([tex]RR[/tex] and [tex]Rr[/tex]), and the trait of white flowers is governed by the allele [tex]r[/tex] ([tex]rr[/tex]).

The horticulturist plans to cross a geranium that is true-breeding for red flowers with a geranium that is heterozygous for red flowers.

Which Punnett square best describes this cross?

[tex]
\[
\begin{array}{c|c|c|}
\multicolumn{1}{c}{} & R & r \\
\cline{2-3}
R & Rr & Rr \\
\cline{2-3}
R & Rr & Rr \\
\cline{2-3}
\end{array}
\]
[/tex]

[tex]
\[
\begin{array}{c|c|c|c|}
\multicolumn{1}{c}{} & R & R & r \\
\cline{2-4}
R & RR & RR & Rr \\
\cline{2-4}
r & Rr & Rr & rr \\
\cline{2-4}
\end{array}
\]
[/tex]

To solve this problem, we're going to determine the possible genetic combinations that result from crossing two geranium plants with specific genetic traits.

### Step 1: Understand the Genetic Makeup of Each Parent
- Parent 1 is "true-breeding" for red flowers, which means it is homozygous with the alleles "RR". This parent can only contribute the allele "R" to its offspring.
- Parent 2 is heterozygous for red flowers, with the alleles "Rr". This parent can contribute either "R" or "r" to its offspring.

### Step 2: Set Up the Punnett Square
A Punnett square helps us visualize the combinations of alleles each parent can contribute.

1. Arrange the alleles of each parent along the top and side of a grid:
- Parent 1 (true-breeding red, RR): contributes "R" and "R"
- Parent 2 (heterozygous, Rr): contributes "R" and "r"

2. The Punnett square will look like this:
```
| | R | r |
|---|---|---|
| R | | |
| R | | |
```

### Step 3: Fill in the Punnett Square
To fill in the squares, combine the alleles from each parent for each cell:
- Top-left cell: R (from Parent 1) + R (from Parent 2) = RR
- Top-right cell: R (from Parent 1) + r (from Parent 2) = Rr
- Bottom-left cell: R (from Parent 1) + R (from Parent 2) = RR
- Bottom-right cell: R (from Parent 1) + r (from Parent 2) = Rr

The completed Punnett square looks like this:

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

### Step 4: Interpreting the Results
The results of this cross yield the following possible genotypes for the offspring:
- 50% RR: These will produce red flowers because both alleles are for red.
- 50% Rr: These will also produce red flowers because the presence of at least one "R" allele results in red flowers.

Therefore, all the offspring will have red flowers, with 100% being either "RR" or "Rr".