Question

In pea plants, round seeds (R) are dominant to wrinkled seeds (r), and yellow seed color (Y) is dominant to green seed color (y) . The gene for seed shape and the gene for seed color follow the law of independent assortment and are not sex-linked. In a cross between two RrYy parents, predict the fraction of offspring with round, yellow seeds.
Responses
A 1/21/2
B 3/43/4
C 9/169/16
D 15/16

Answer 1

To solve this problem, we can use a Punnett square to determine the frequencies of the phenotypes (visible traits) in the offspring resulting from the cross between the two RrYy parents.

### Parent Genotypes
Both parents are heterozygous for seed shape and seed color, so their genotypes are RrYy.

### Possible Gametes
Each parent can produce four types of gametes:
- RY (Round, Yellow)
- Ry (Round, Green)
- rY (Wrinkled, Yellow)
- ry (Wrinkled, Green)

### Punnett Square
We can create a Punnett square with the gametes from each parent:

\[
\begin{array}{c|c|c|c|c}
& RY & Ry & rY & ry \\
\hline
RY & RRYY & RRYy & RrYY & RrYy \\
\hline
Ry & RRYy & RRyy & RrYy & Rryy \\
\hline
rY & RrYY & RrYy & rrYY & rrYy \\
\hline
ry & RrYy & Rryy & rrYy & rryy \\
\end{array}
\]

### Offspring Phenotypes
Now we can analyze the resulting offspring from the Punnett square:
1. **Round, Yellow (R_Y_)**:
- **RRYY**: 1
- **RRYy**: 2
- **RrYY**: 1
- **RrYy**: 2
Total = 6 Round, Yellow

2. **Round, Green (R_yy)**:
- **RRYy**: 2
- **RrYy**: 2
Total = 2 Round, Green

3. **Wrinkled, Yellow (rrY_)**:
- **RrYY**: 1
- **RrYy**: 2
Total = 3 Wrinkled, Yellow

4. **Wrinkled, Green (rryy)**:
- **rrYY**: 1
- **rrYy**: 1
Total = 2 Wrinkled, Green

### Summary of Phenotypes
- Round Yellow: 6
- Round Green: 2
- Wrinkled Yellow: 3
- Wrinkled Green: 1

Total = 6 + 2 + 3 + 1 = 12.

### Fraction of Offspring with Round, Yellow Seeds
The fraction of offspring with round, yellow seeds:
\[
\text{Fraction} = \frac{\text{Number of Round, Yellow}}{\text{Total Offspring}} = \frac{6}{16} = \frac{3}{8}.
\]

However, let's double-check:

### Total number of offspring types
By combinatorial genetics and mapping out, we find that 9 out of the 16 squares correspond to Round seeds (R_) and each combination gives 3 contributions leading to Yellow seeds (Y_). Thus:

The correct fraction for Round, Yellow seeds is indeed:

\[
\frac{9}{16}.
\]

### Final Answer
**C)** \( \frac{9}{16} \)