Question

n 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 predict the fraction of offspring with round, yellow seeds from a cross between two RrYy parents, we can use a Punnett square to determine the possible genotypes of the offspring.

The alleles from each parent can be represented as follows:
- R (round) and r (wrinkled) for seed shape
- Y (yellow) and y (green) for seed color

Since both parents are RrYy, we can list all the possible gametes they can produce:
- From parent 1: RY, Ry, rY, ry
- From parent 2: RY, Ry, rY, ry

Now we can set up a 4x4 Punnett square:

| | RY | Ry | rY | ry |
|-------|-----|-----|-----|-----|
| **RY** | RRY Y | RRYy | RrY Y | RrYy |
| **Ry** | RRYy | Rryy | RrYy | Rryy |
| **rY** | RrY Y | RrYy | rrY Y | rrYy |
| **ry** | RrYy | Rryy | rrYy | rryy |

Now we need to identify which of these combinations result in round and yellow seeds. Seeds will be round if they have at least one R allele (Rr or RR) and yellow if they have at least one Y allele (Yy or YY).

Evaluating the combinations:

1. RRY Y - Round and Yellow
2. RRYy - Round and Yellow
3. RrY Y - Round and Yellow
4. RrYy - Round and Yellow
5. RRYy - Round and Yellow
6. RrYy - Round and Yellow
7. RrY Y - Round and Yellow
8. rrY Y - Wrinkled and Yellow
9. RrYy - Round and Yellow
10. rrY y - Wrinkled and Green
11. rrYy - Wrinkled and Yellow
12. rryy - Wrinkled and Green

Now counting all the combinations, we find:

- Round Yellow: RRY Y (1), RRYy (2), RrY Y (3), RrYy (4), RrYy (5) = 9 combinations
- Total combinations = 16

The fraction of offspring with round, yellow seeds is therefore:
\[
\frac{9}{16}
\]

Thus, the answer is **C**: \( \frac{9}{16} \).