Mendel first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only round-yellow seeds were cross-bred by self pollination, then peas having round-yellow seeds, round green seeds, wrinkled-yellow seeds and wrinkled-green seeds were produced. Mendel collected a total of 2160 seeds.
(a) What will be the number of (i) round green seeds (ii) wrinkled green seeds (iii) round yellow seeds, and (iv) wrinkled-yellow seeds ?
(b) Which 'ratio' as established by Mendel have you made use of in answering the part (a) above ?

Answer

To solve the problem, we will follow these steps:

### Step 1: Understand the Cross
Mendel crossed pure-bred pea plants with round-yellow seeds (dominant traits) with pure-bred plants having wrinkled-green seeds (recessive traits). The dominant traits are represented as:
- Round seeds: R (dominant)
- Yellow seeds: Y (dominant)

The recessive traits are represented as:
- Wrinkled seeds: r (recessive)
- Green seeds: y (recessive)

### Step 2: Determine the Genotypes of the Parents
The genotypes of the parent plants are:
- Round-yellow seeds: RRYY (homozygous dominant)
- Wrinkled-green seeds: rryy (homozygous recessive)

### Step 3: Determine the F1 Generation
When these two plants are crossed, all offspring (F1 generation) will have the genotype RrYy (heterozygous for both traits) and will exhibit the dominant phenotype, which is round-yellow seeds.

### Step 4: Self-Pollination of F1 Generation
When the F1 generation (RrYy) is self-pollinated, we can use a Punnett square to determine the phenotypic ratio of the offspring. The gametes produced by RrYy will be RY, Ry, rY, and ry.

### Step 5: Determine the F2 Generation Ratio
The phenotypic ratio from the dihybrid cross (RrYy x RrYy) is:
- Round Yellow (RY): 9
- Round Green (rY): 3
- Wrinkled Yellow (Ry): 3
- Wrinkled Green (ry): 1

This gives us a total ratio of 9:3:3:1.

### Step 6: Calculate the Number of Each Type of Seed
Given that Mendel collected a total of 2160 seeds, we can calculate the number of seeds for each phenotype using the ratio:

1. **Round Yellow Seeds**:
\[ \text{Number of Round Yellow Seeds} = \frac{9}{16} \times 2160 = 1215 \]

2. **Round Green Seeds**:
\[ \text{Number of Round Green Seeds} = \frac{3}{16} \times 2160 = 405 \]

3. **Wrinkled Yellow Seeds**:
\[ \text{Number of Wrinkled Yellow Seeds} = \frac{3}{16} \times 2160 = 405 \]

4. **Wrinkled Green Seeds**:
\[ \text{Number of Wrinkled Green Seeds} = \frac{1}{16} \times 2160 = 135 \]

### Final Results
- (i) Round Green Seeds: 405
- (ii) Wrinkled Green Seeds: 135
- (iii) Round Yellow Seeds: 1215
- (iv) Wrinkled Yellow Seeds: 405

### Step 7: Identify the Ratio
The ratio established by Mendel that we used in this calculation is the **phenotypic ratio of 9:3:3:1** from a dihybrid cross.

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