To determine the ratio of yellow seeds to green seeds in the offspring of two heterozygous pea plants (Yy), we need to examine the possible genotypes that could result from such a cross.
1. Construct a Punnett square for the cross [tex]\(Yy \times Yy\)[/tex].
- One parent's alleles (Y and y) are placed on the top of the square.
- The other parent's alleles (Y and y) are placed on the side of the square.
The Punnett square looks like this:
[tex]\[
\begin{array}{c|c|c}
& Y & y \\
\hline
Y & YY & Yy \\
\hline
y & Yy & yy \\
\end{array}
\][/tex]
2. Fill in the Punnett square:
- Top row: YY (from Y x Y) and Yy (from Y x y).
- Bottom row: Yy (from y x Y) and yy (from y x y).
This gives us the following results for the genotypes of the offspring:
[tex]\[
YY, Yy, Yy, yy
\][/tex]
3. Identify the phenotypes:
- YY is yellow because the presence of at least one dominant Y allele results in yellow seeds.
- Yy is also yellow for the same reason, as the Y allele is dominant over the y allele.
- yy is green because it contains two recessive alleles (y).
4. Calculate the ratio of yellow seeds to green seeds:
- There are three genotypes that produce yellow seeds (YY, Yy, Yy).
- There is one genotype that produces green seeds (yy).
5. The ratio of yellow seeds to green seeds is thus:
- Yellow: 3
- Green: 1
Therefore, the expected ratio of yellow seeds to green seeds in the offspring is [tex]\(\boxed{3:1}\)[/tex].
Hence, the correct answer is:
D. [tex]\(3:1\)[/tex]
