To answer this question, let's analyze the given statements related to the Punnett squares for the plant's stem length.
### 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]
### Analysis of the First Generation:
- All offspring have the genotype Tt, indicating that they all have tall stems because the dominant allele [tex]\( T \)[/tex] expresses the tall trait.
### 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]
### Analysis of the Second Generation:
- The genotypes are TT, Tt, Tt, and tt.
- TT and Tt result in tall stems since the [tex]\( T \)[/tex] allele is dominant.
- tt results in short stems since both alleles are recessive.
Now, let's evaluate the given statements:
1. Plants with short stems are homozygous for that trait.
- True: From the Punnett squares, we see that the only genotype for short stems (recessive trait) is [tex]\( tt \)[/tex], which means plants must be homozygous recessive to show short stems.
2. Plants with tall stems are always homozygous for that trait.
- False: Tall stems can result from genotypes TT (homozygous dominant) or Tt (heterozygous). Therefore, not all tall plants are homozygous.
3. Both parent plants in the second generation are heterozygous.
- False: Based on the Punnett square for the second generation, the parents must be Tt and Tt (heterozygous) to produce the observed offspring genotypes. Thus, not both parent plants are always heterozygous.
4. Both parent plants in the second generation are homozygous.
- False: As we concluded, the parent plants in the second generation are Tt (heterozygous) and Tt (heterozygous). Therefore, they are not homozygous.
By examining the statements, the only true statement is:
- Plants with short stems are homozygous for that trait.
Thus, the solution indicates that only the first statement is true.
