College

A horticulturalist 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 [tex]r[/tex] ([tex]rr[/tex]).

The horticulturalist crosses two geraniums from the F1 generation. Look at the Punnett square to see this cross:

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

Which ratio of red-to-white flowering plants would she expect to see in the phenotypes of the F2 generation?

A. 3 red: 1 white
B. 1 red: 3 white

Answer :

To determine the ratio of red-to-white flowering plants in the F2 generation, we can use a Punnett square to analyze the genetic cross between two geraniums.

Let's break it down:

1. Understanding the Alleles:
- The allele for red flowers is represented by [tex]\( R \)[/tex]. Both homozygous dominant ([tex]\( RR \)[/tex]) and heterozygous ([tex]\( Rr \)[/tex]) combinations will result in red flowers.
- The allele for white flowers is represented by [tex]\( r \)[/tex]. Only the homozygous recessive ([tex]\( rr \)[/tex]) combination will result in white flowers.

2. Setting up the Cross:
- Given the parentheses around "F1 generation," let's assume each parent in the F1 generation is heterozygous for this trait ([tex]\( Rr \)[/tex]).

3. Completing the Punnett Square:
- We cross the alleles of two [tex]\( Rr \)[/tex] plants:
- Parent 1 alleles: [tex]\( R \)[/tex] and [tex]\( r \)[/tex]
- Parent 2 alleles: [tex]\( R \)[/tex] and [tex]\( r \)[/tex]

The Punnett square would look like this:
```
| | R | r |
|---|-----|-----|
| R | RR | Rr |
| r | Rr | rr |
```

4. Analyzing the Results:
- Let's count the genotypes resulting from the square:
- [tex]\( RR \)[/tex]: 1 combination
- [tex]\( Rr \)[/tex]: 2 combinations
- [tex]\( rr \)[/tex]: 1 combination

5. Determining the Phenotypes:
- Red flowers ([tex]\( RR \)[/tex] and [tex]\( Rr \)[/tex]): 3 total combinations
- White flowers ([tex]\( rr \)[/tex]): 1 combination

6. Calculating the Ratio:
- The expected ratio of red to white flowering plants in the F2 generation is 3 red to 1 white, or [tex]\(3:1\)[/tex].

Therefore, the horticulturalist can expect a 3:1 ratio of red-to-white flowers in the phenotypes of the F2 generation.

Other Questions