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In pea plants, the allele for yellow seeds (Y) is dominant and the allele for green seeds (y) is recessive. Two plants with the following genotypes are crossed:
Yy × Yy

What ratio of yellow seeds to green seeds should you expect in the offspring?

A. 1:3
B. 2:2
C. 4:0
D. 3:1


Sagot :

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]