To determine the phenotype ratio of the given cross between two cacti, we need to consider the possible genetic combinations that can result from this cross. The Punnett square helps us visualize these combinations.
Here is the Punnett square with the correct alleles placed:
[tex]\[
\begin{array}{|c|c|c|}
\hline
& L & l \\
\hline
L & LL & Ll \\
\hline
l & Ll & ll \\
\hline
\end{array}
\][/tex]
1. Determine the possible genotypes:
- The Punnett square shows the possible combinations of alleles:
- Top left cell: [tex]\(LL\)[/tex]
- Top right cell: [tex]\(Ll\)[/tex]
- Bottom left cell: [tex]\(Ll\)[/tex]
- Bottom right cell: [tex]\(ll\)[/tex]
2. Count the occurrences of each genotype:
- [tex]\(LL\)[/tex] appears once
- [tex]\(Ll\)[/tex] appears twice
- [tex]\(ll\)[/tex] appears once
3. Determine the phenotypes associated with these genotypes:
- For long needles: Since the allele [tex]\(L\)[/tex] (long needles) is dominant over [tex]\(l\)[/tex] (short needles), both [tex]\(LL\)[/tex] and [tex]\(Ll\)[/tex] will result in long needles.
- For short needles: Only the genotype [tex]\(ll\)[/tex] will result in short needles.
4. Count the phenotypes:
- Long needles ([tex]\(LL\)[/tex] and [tex]\(Ll\)[/tex]): There are 3 instances (1 from [tex]\(LL\)[/tex] and 2 from [tex]\(Ll\)[/tex]).
- Short needles ([tex]\(ll\)[/tex]): There is 1 instance.
5. Phenotype Ratio:
- There are 3 long needles to 1 short needle.
Based on this analysis, the phenotype ratio for this cross is:
Three long, one short.
So, the correct answer is:
B. Three long, one short.
