To solve this problem, we need to analyze the given Punnett square to determine the phenotype ratio of the offspring based on their needle lengths.
The Punnett square provided in the question is:
[tex]\[
\begin{array}{|c|c|}
\hline
L & L \\
\hline
L & L \\
\hline
U & L \\
\hline
\end{array}
\][/tex]
From this Punnett square, we see that both parents contribute the allele [tex]$L$[/tex] for long needles. Here's a detailed step-by-step breakdown of the analysis:
1. Identify the alleles contributed by each parent:
- The parent cacti contribute the allele [tex]$L$[/tex] (for long needles) or the allele [tex]$l$[/tex] (for short needles).
2. Combine the alleles for each possible offspring genotype:
- The Punnett square shows all possible combinations of the alleles contributed by the parents.
- The allele combinations from the given Punnett square are:
- Top-left cell: [tex]$L \& L$[/tex]
- Top-right cell: [tex]$L \& L$[/tex]
- Bottom-left cell: [tex]$L \& L$[/tex]
- Bottom-right cell: [tex]$L \& L$[/tex]
3. Determine the genotype of the offspring:
- Since each cell in the Punnett square contains the combination [tex]$L \& L$[/tex], all offspring have the genotype [tex]$LL$[/tex].
4. Determine the phenotype of each genotype:
- The [tex]$LL$[/tex] genotype results in long needles because the presence of the [tex]$L$[/tex] allele dominates any possible short allele ([tex]$l$[/tex]).
5. Count the ratio of phenotypes:
- In the Punnett square, all four possibilities result in long needles.
- Hence, the phenotype ratio is 4 long needles to 0 short needles.
6. Match the ratio to the given options:
- The given options are:
- A. Two long, two short
- B. One long, three short
- C. Four long, zero short
- D. Three long, one short
Given our analysis, the correct phenotype ratio of the offspring is 4 long needles to 0 short needles.
Therefore, the correct choice is:
C. Four long, zero short
