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



Answer :

Let's work through this problem step by step:

1. Identify the parent genotypes and alleles:
- Both parent plants have the genotype [tex]\( Yy \)[/tex], meaning they each have one dominant allele [tex]\( Y \)[/tex] for yellow seeds and one recessive allele [tex]\( y \)[/tex] for green seeds.

2. Set up a Punnett square to determine possible genotypes of the offspring:

The Punnett square for the cross [tex]\( Yy \times Yy \)[/tex] looks like this:

[tex]\[ \begin{array}{c|c|c} & Y & y \\ \hline Y & YY & Yy \\ \hline y & Yy & yy \\ \end{array} \][/tex]

3. List the genotypes identified in the Punnett square:
- The possible genotypes of the offspring are [tex]\( YY \)[/tex], [tex]\( Yy \)[/tex], [tex]\( Yy \)[/tex], and [tex]\( yy \)[/tex].

4. Determine the phenotypes associated with each genotype:
- Genotype [tex]\( YY \)[/tex]: Yellow seeds (since it has two dominant [tex]\( Y \)[/tex] alleles).
- Genotype [tex]\( Yy \)[/tex]: Yellow seeds (since it has one dominant [tex]\( Y \)[/tex] allele).
- Genotype [tex]\( Yy \)[/tex]: Yellow seeds (same reason as above).
- Genotype [tex]\( yy \)[/tex]: Green seeds (since it has two recessive [tex]\( y \)[/tex] alleles).

5. Count the number of each phenotype:
- Yellow seeds: [tex]\( YY \)[/tex], [tex]\( Yy \)[/tex], [tex]\( Yy \)[/tex] (total = 3)
- Green seeds: [tex]\( yy \)[/tex] (total = 1)

6. Calculate the ratio of yellow seeds to green seeds:
- The ratio of yellow seeds to green seeds is [tex]\( 3:1 \)[/tex].

Thus, the ratio of yellow seeds to green seeds in the offspring is [tex]\( 3:1 \)[/tex].

The correct answer is:
B. [tex]\( 3:1 \)[/tex]

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