Select all the correct answers.

A particular plant has two alleles that control the length of its stem. T represents the dominant allele for a tall stem, and t represents the recessive allele for a short stem. Based on the Punnett squares, which two statements are true about the genotype of the plant's stem length?

[tex]\[
\begin{array}{|c|c|c|}
\hline
\text{First Generation} & t & t \\
\hline
T & Tt & Tt \\
\hline
T & Tt & Tt \\
\hline
\end{array}
\][/tex]

[tex]\[
\begin{array}{|c|c|c|}
\hline
\text{Second Generation} & T & t \\
\hline
T & TT & Tt \\
\hline
t & Tt & tt \\
\hline
\end{array}
\][/tex]

- Plants with short stems are homozygous for that trait.
- Plants with tall stems are always homozygous for that trait.
- Both parent plants in the second generation are heterozygous.
- Both parent plants in the second generation are homozygous.

Let's analyze the question step-by-step:

Firstly, we need to understand the Punnett squares provided for the first and second generations:

### First Generation Punnett Square
[tex]\[ \begin{array}{|c|c|c|} \hline & t & t \\ \hline T & Tt & Tt \\ \hline T & Tt & Tt \\ \hline \end{array} \][/tex]

This shows that the first generation plants have genotypes:
- [tex]$ Tt $[/tex]
- [tex]$ Tt $[/tex]
- [tex]$ Tt $[/tex]
- [tex]$ Tt $[/tex]

All possible offspring in the first generation are heterozygous ([tex]$ Tt $[/tex]). Since [tex]$ T $[/tex] (tall stem) is dominant over [tex]$ t $[/tex] (short stem), all the first-generation plants will have tall stems.

### Second Generation Punnett Square
[tex]\[ \begin{array}{|c|c|c|} \hline & T & t \\ \hline T & TT & Tt \\ \hline t & Tt & tt \\ \hline \end{array} \][/tex]

This shows that the second generation plants have genotypes:
- [tex]$ TT $[/tex]
- [tex]$ Tt $[/tex]
- [tex]$ Tt $[/tex]
- [tex]$ tt $[/tex]

From the second-generation Punnett square, we see the following phenotypes for stem length:
- [tex]$ TT $[/tex]: Tall stem (homozygous)
- [tex]$ Tt $[/tex]: Tall stem (heterozygous)
- [tex]$ Tt $[/tex]: Tall stem (heterozygous)
- [tex]$ tt $[/tex]: Short stem (homozygous)

Now let's analyze the statements:

1. Plants with short stems are homozygous for that trait.
- Correct. A plant will have short stems if and only if it has the genotype [tex]$ tt $[/tex], which is homozygous recessive.

2. Plants with tall stems are always homozygous for that trait.
- Incorrect. Plants with tall stems can be either homozygous dominant ([tex]$ TT $[/tex]) or heterozygous ([tex]$ Tt $[/tex]). Thus, tall-stemmed plants are not always homozygous.

3. Both parent plants in the second generation are heterozygous.
- Incorrect. The second generation Punnett square is created by crossing [tex]$ Tt $[/tex] (tall stem, heterozygous) and [tex]$ Tt $[/tex] (tall stem, heterozygous). As a result, both parent plants are heterozygous.

4. Both parent plants in the second generation are homozygous.
- Incorrect. As mentioned, both parent plants in the second generation are [tex]$ Tt $[/tex] (heterozygous).

So, the correct statements are:

- "Plants with short stems are homozygous for that trait."

Given the step-by-step explanation, this concludes the detailed solution.