College

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 true-breeding for white flowers. Which Punnett square best describes this cross?

A.
[tex]
\[
\begin{tabular}{|c|c|c|}
\hline
& $R$ & $r$ \\
\hline
$R$ & $RR$ & $Rr$ \\
\hline
$r$ & $Rr$ & $\pi$ \\
\hline
\end{tabular}
\]
[/tex]

B. (Continue with other options if needed)

Answer :

To solve the problem of determining the Punnett square for crossing a true-breeding red-flowered geranium with a true-breeding white-flowered geranium, follow these steps:

1. Identify Parent Genotypes:
- The red-flowered geranium is true-breeding, meaning it has two dominant alleles. Its genotype is [tex]\( RR \)[/tex].
- The white-flowered geranium is also true-breeding, but with two recessive alleles. Its genotype is [tex]\( rr \)[/tex].

2. Set Up the Punnett Square:
- A Punnett square is a grid that shows all possible combinations of alleles from the parents.
- You place the alleles from one parent along the top and the alleles from the other parent along the side.

3. Fill in the Punnett Square:
- Cross each allele from the red-flowered parent (on the top) with each allele from the white-flowered parent (on the side).
- Since the red-flowered parent is [tex]\( RR \)[/tex], both alleles you list across the top of the Punnett square will be [tex]\( R \)[/tex].
- Since the white-flowered parent is [tex]\( rr \)[/tex], both alleles you list down the side of the Punnett square will be [tex]\( r \)[/tex].

4. Determine Offspring Genotypes:
- Fill in each box of the Punnett square by combining the alleles from the top and side of the grid.
- In this case, every box in the Punnett square will be filled with [tex]\( Rr \)[/tex] as each offspring receives one allele [tex]\( R \)[/tex] from the red-flowered parent and one allele [tex]\( r \)[/tex] from the white-flowered parent.

5. Outcome:
- All offspring will have the genotype [tex]\( Rr \)[/tex]. This means all offspring will exhibit red flowers (since the [tex]\( R \)[/tex] allele for red is dominant).

Using the details above, you can match the Punnett square and conclude the correct answer would illustrate a grid where each possibility for the offspring’s genotype is [tex]\( Rr \)[/tex]. This matches none of the examples typically given in options A, B, etc., but the conceptual understanding is critical.