Dihybrid cross is made between RRYY (yellow round seed) and yyrr (wrinkled green seed ) of Pea. `F_(2)` ratio amongst round yellow, round green, wrinkled yellow and wrinkled green would be

Options

A. `9:3:3:1`
B. `15:1:0:0`
C. `9:3:4:0`
D. `4:4:4:4`

Answer

To solve the problem of determining the F2 ratio from a dihybrid cross between RRYY (yellow round seed) and yyrr (wrinkled green seed) in pea plants, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Traits and Their Alleles:**
- Round seed (R) is dominant over wrinkled seed (r).
- Yellow seed (Y) is dominant over green seed (y).
- Therefore, the parental genotypes are:
- Parent 1: RRYY (homozygous dominant for both traits)
- Parent 2: yyrr (homozygous recessive for both traits)

2. **Determine the Gametes Produced by Each Parent:**
- Parent 1 (RRYY) can only produce one type of gamete: RY.
- Parent 2 (yyrr) can only produce one type of gamete: yr.

3. **Perform the F1 Cross:**
- The F1 generation results from crossing the gametes from both parents:
- F1 genotype: All offspring will be RrYy (heterozygous for both traits).
- All F1 plants will exhibit the dominant traits: round and yellow seeds.

4. **Self-Cross the F1 Generation to Obtain F2:**
- The F1 plants (RrYy) are self-crossed to produce the F2 generation.
- The gametes produced by F1 (RrYy) can be: RY, Ry, rY, and ry.

5. **Construct a Punnett Square for the F2 Generation:**
- Create a 4x4 Punnett square using the gametes from the F1 generation:
```
RY Ry rY ry
------------------------
RY | RRYY RRYy RrYY RrYy
------------------------
Ry | RRYy RRyy RrYy Rryy
------------------------
rY | RrYY RrYy rrYY rrYy
------------------------
ry | RrYy Rryy rrYy rryy
```

6. **Count the Phenotypes:**
- From the Punnett square, we can count the phenotypes:
- Round Yellow (RRYY, RRYy, RrYY, RrYy): 9
- Round Green (RRyy, Rryy): 3
- Wrinkled Yellow (rrYY, rrYy): 3
- Wrinkled Green (rryy): 1

7. **Determine the F2 Ratio:**
- The ratio of phenotypes in the F2 generation is:
- Round Yellow : Round Green : Wrinkled Yellow : Wrinkled Green = 9 : 3 : 3 : 1

### Final Answer:
The F2 ratio amongst round yellow, round green, wrinkled yellow, and wrinkled green seeds is **9:3:3:1**.

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