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

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

\begin{tabular}{|c|c|c|}
\hline Second Generation & T & [tex]$t$[/tex] \\
\hline T & T & Tt \\
\hline t & Tt & tt \\
\hline
\end{tabular}

1. Plants with short stems are homozygous for that trait.
2. Plants with tall stems can be either homozygous or heterozygous.



Answer :

GinnyAnswer
Let's break down the question step-by-step, using Punnett squares to analyze the genotypes of plant stem length.

First Generation Analysis:

For the given Punnett square:
[tex]\[ \begin{array}{|c|c|c|} \hline & t & t \\ \hline T & Tt & Tt \\ \hline T & Tt & Tt \\ \hline \end{array} \][/tex]

Here, all offspring are Tt, which means they all have one dominant allele (T) and one recessive allele (t). Since T is dominant, all plants will exhibit the tall phenotype. Therefore, the genotypes of the first generation are:
- Tt (100%) – All tall.

Second Generation Analysis:

For the 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]

In this scenario, the possible genotypes are:
- TT – Homozygous dominant (tall)
- Tt – Heterozygous (tall)
- tt – Homozygous recessive (short)

Let's break these down by the percentage of occurrences:
- TT: 1 out of 4 squares = 25% – Tall
- Tt: 2 out of 4 squares = 50% – Tall
- tt: 1 out of 4 squares = 25% – Short

Analyzing the Given Statement:

Statement: "Plants with short stems are homozygous for that trait"

From our analysis of the second generation, we see that a plant exhibits a short stem only if it has the genotype tt. This genotype consists of two recessive alleles (t), making it homozygous recessive. Therefore, this statement is true.

Conclusion:

Based on the detailed Punnett square analysis and the separation of different genotypes, we can conclude that:

1. Plants with short stems are homozygous for that trait, which makes sense given the genotype tt is required for a plant to have a short stem.