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] (both [tex]$R R$[/tex] and [tex]$R r$[/tex]) and the trait of white flowers is governed by the allele [tex]$r$[/tex].

The horticulturalist crosses two geraniums from the F1 generation.

Look at the Punnett square to see this cross:

[tex]\[

\begin{tabular}{|c|c|c|}

\hline

& $R$ & $r$ \\

\hline

$R$ & $R R$ & $R r$ \\

\hline

$r$ & $R r$ & $r r$ \\

\hline

\end{tabular}

\][/tex]

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

A. All red

B. 3 red : 1 white

C. 2 red : 2 white

D. 1 red : 3 white

Answer :

To determine the ratio of red-to-white flowering plants in the F2 generation, we can look at the Punnett square provided for the cross of two geraniums from the F1 generation. The alleles involved are:

- [tex]\( R \)[/tex] for red flowers.
- [tex]\( r \)[/tex] for white flowers.

The Punnett square shows us the possible combinations of alleles:

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

From the Punnett square, we can see the possible genotypes for the F2 generation:

1. [tex]\( RR \)[/tex] - This genotype represents red flowers.
2. [tex]\( Rr \)[/tex] - This genotype also represents red flowers because the presence of at least one [tex]\( R \)[/tex] results in red flowers.
3. [tex]\( rr \)[/tex] - This genotype represents white flowers.

Counting how many of each genotype we have:

- 1 [tex]\( RR \)[/tex] (red)
- 2 [tex]\( Rr \)[/tex] (red)
- 1 [tex]\( rr \)[/tex] (white)

If we combine the red genotypes ([tex]\( RR \)[/tex] and [tex]\( Rr \)[/tex]) together:

- Total red flowering plants: 1 ([tex]\( RR \)[/tex]) + 2 ([tex]\( Rr \)[/tex]) = 3
- Total white flowering plants: 1 ([tex]\( rr \)[/tex]) = 1

Thus, the ratio of red to white flowering plants in the F2 generation is 3:1. Therefore, the horticulturalist can expect to see this ratio in the phenotypes of the F2 generation.

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