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The Punnett square predicts the ratio of genotypes in the offspring based on the genotypes of the parents. Which Punnett square represents a cross between a mom who is heterozygous for dimples (Dd) and a dad who is homozygous for no dimples (dd)?

A.
\begin{tabular}{|c|c|}
\hline Dd & Dd \\
\hline Dd & Dd \\
\hline
\end{tabular}

B.
\begin{tabular}{|c|c|}
\hline Dd & dd \\
\hline Dd & dd \\
\hline
\end{tabular}

Sagot :

GinnyAnsweridn
To create a Punnett square for a genetic cross, we need to use the parental genotypes to determine the possible genotypes of their offspring.

In this scenario:
- The mother is heterozygous for dimples, which means her genotype is [tex]\( Dd \)[/tex].
- The father is homozygous for no dimples, so his genotype is [tex]\( dd \)[/tex].

We can draw the Punnett square by setting the alleles from one parent across the top and the alleles from the other parent down the side.

Here's a step-by-step solution:

1. Write the alleles for the mother [tex]\( Dd \)[/tex] along the top of the grid:
[tex]\[ D \quad d \][/tex]

2. Write the alleles for the father [tex]\( dd \)[/tex] along the side of the grid:
[tex]\[ \begin{array}{c} d \\ d \\ \end{array} \][/tex]

3. Fill in the squares by combining the alleles from the top and the side:

[tex]\[ \begin{array}{c|c|c} & D & d \\ \hline d & Dd & dd \\ \hline d & Dd & dd \\ \hline \end{array} \][/tex]

So, the Punnett square for a cross between a heterozygous mother for dimples (Dd) and a homozygous no-dimples father (dd) will be:

[tex]\[ \begin{array}{|c|c|} \hline Dd & dd \\ \hline Dd & dd \\ \hline \end{array} \][/tex]

This Punnett square shows that there are two possible genotypes for the offspring: [tex]\( Dd \)[/tex] (heterozygous) and [tex]\( dd \)[/tex] (homozygous recessive). The ratio of these genotypes is 1:1. Thus, half of the offspring will have dimples (since [tex]\( D \)[/tex] is dominant) and half will not have dimples (since both alleles are [tex]\( d \)[/tex]).
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