A plant can have either broad leaves (B) or narrow leaves (b). A plant with genotype BB is crossed with a plant with genotype Bb. Which Punnett square correctly represents this cross?

A.
\begin{tabular}{|c|c|c|}
\hline & B & b \\
\hline B & Bb & Bb \\
\hline B & Bb & Bb \\
\hline
\end{tabular}

B.
\begin{tabular}{|c|c|c|}
\hline \multicolumn{3}{|c|}{B} \\
\hline & BB & Bb \\
\hline & BB & Bb \\
\hline
\end{tabular}

C.
\begin{tabular}{|c|c|c|}
\hline & b & b \\
\hline B & Bb & Bb \\
\hline B & Bb & Bb \\
\hline
\end{tabular}

D.
\begin{tabular}{|c|c|c|}
\hline & B & b \\
\hline B & BB & Bb \\
\hline B & BB & Bb \\
\hline
\end{tabular}



Answer :

To determine the correct Punnett square for the given genotypes, [tex]$BB$[/tex] and [tex]$Bb$[/tex], let's examine the cross step by step:

1. Identify the allele combinations from each parent:
- Parent 1 (BB): This parent can only contribute a 'B' allele.
- Parent 2 (Bb): This parent can contribute either a 'B' or a 'b' allele.

2. Set up the Punnett square:
We'll set up a 2x2 Punnett square where one parent’s alleles are along the top and the other parent’s alleles are along the side. For simplicity, let’s keep Parent 1's alleles on the side (vertical) and Parent 2's alleles on the top (horizontal).

3. Lay out the combinations in the square:

[tex]\[ \begin{array}{c|c|c} & B & b \\ \hline B & BB & Bb \\ \hline B & BB & Bb \\ \hline \end{array} \][/tex]

4. Create and analyze the Punnett square:

- Top row 'B' crossed with Parent 1's 'B': BB
- Top row 'b' crossed with Parent 1's 'B': Bb
- Bottom row 'B' crossed with Parent 1's 'B': BB
- Bottom row 'b' crossed with Parent 1's 'B': Bb

The resultant Punnett square indicates that the offspring will have the following genotypes:
- Two BB
- Two Bb

5. Match the Punnett squares provided in the options with our results:

Option B correctly matches our derived Punnett square:

[tex]\[ \begin{tabular}{|c|c|c|} \hline \multicolumn{3}{|c|}{$B$} \\ \hline & BB & $Bb$ \\ \hline & $BB$ & $Bb$ \\ \hline \end{tabular} \][/tex]

Therefore, the correct answer is Option B which corresponds to the entry `2`.