College

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 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. 2 red: 2 white
B. 3 red: 1 white
C. 1 red: 3 white

Answer :

To solve this problem, we need to analyze the Punnett square provided in the question. The Punnett square shows the possible genotypes from crossing two geraniums from the F1 generation. Here’s a step-by-step explanation of how to determine the expected ratio of red-to-white flowering plants:

1. Identify the Alleles:
- The allele for red flowers is represented by 'R'.
- The allele for white flowers is represented by 'r'.
- Red flowers are produced when at least one 'R' is present (i.e., genotypes RR or Rr).
- White flowers are produced only with the genotype 'rr'.

2. Analyze the Punnett Square:
The construction of the Punnett square from the question is as follows:

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

3. List the Possible Genotypes:
From the Punnett square, the possible genotypes and their frequency of occurrence are:
- RR: 1 occurrence
- Rr: 2 occurrences (there are two Rr combinations)
- rr: 1 occurrence

4. Determine the Phenotypes:
- Red-flowering genotypes are RR and Rr.
- White-flowering genotype is rr.
- From the genotypes, we have:
- 3 potential red-flowering plants (1 RR and 2 Rr)
- 1 potential white-flowering plant (1 rr)

5. Calculate the Phenotypic Ratio:
- The ratio of red-flowering to white-flowering plants is 3 red : 1 white.

Therefore, the expected ratio of red-to-white flowering plants in the F2 generation is 3 red: 1 white.