To find the phenotype ratio for this cross involving a cactus with long needles (L) and a cactus with short needles (I), we should start by completing the Punnett square and then analyzing the resulting genotypes.
Given the partially completed Punnett square:
[tex]\[
\begin{array}{|c|c|c|}
\hline
L & L \\ \hline
L & LL & \text{?} \\ \hline
I & \text{?} & II \\ \hline
\end{array}
\][/tex]
We need to fill in the '?' cells with the correct genotypes.
1. First row and second column:
- The combination in the second column (L from the top and I from the side) would be "LI".
2. Second row and first column:
- The combination in the first column (L from the side and I from the top) would also be "LI".
The completed Punnett square will look like this:
[tex]\[
\begin{array}{|c|c|c|}
\hline
& L & I \\ \hline
L & LL & LI \\ \hline
I & LI & II \\ \hline
\end{array}
\][/tex]
Next, we analyze the genotypes:
- [tex]\( LL \)[/tex] corresponds to long needles.
- [tex]\( LI \)[/tex] also corresponds to long needles, assuming L (long) is dominant over I (short).
- [tex]\( II \)[/tex] corresponds to short needles.
From the Punnett square, the genotypes are:
- [tex]\( LL \)[/tex]
- [tex]\( LI \)[/tex]
- [tex]\( LI \)[/tex]
- [tex]\( II \)[/tex]
Counting the phenotypes:
- Long needles:
[tex]\( LL \)[/tex] -> 1 instance
[tex]\( LI \)[/tex] -> 2 instances
(Total: 3 instances)
- Short needles:
[tex]\( II \)[/tex] -> 1 instance
(Total: 1 instance)
The phenotype ratio is:
- 3 long needles : 1 short needle
Therefore, the phenotype ratio for this cross is:
A. Three long, one short
