How many phenotyes w.r.t. flower colour are possible if heterozygous Lathyrus odoratus for two loci is selfed ?

Options

A. 3
B. 1
C. 4
D. 2

Answer

To solve the problem of how many phenotypes with respect to flower color are possible when selfing a heterozygous Lathyrus odoratus (sweet pea) for two loci, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Genetics of Flower Color**:
- Lathyrus odoratus has two flower colors: purple and white.
- The flower color is determined by two loci (genes), which we will denote as P and W.

2. **Identify the Alleles**:
- For each locus, there are two alleles: dominant (capital letter) and recessive (lowercase letter).
- The dominant alleles are P (for the first locus) and W (for the second locus).
- The recessive alleles are p and w.

3. **Determine the Genotypes**:
- The possible genotypes for a heterozygous plant at both loci would be:
- PpWw (heterozygous for both loci).

4. **Set Up the Punnett Square**:
- When selfing the PpWw plant, we can create a Punnett square to determine the offspring's genotypes.
- Each parent (PpWw) can produce four types of gametes: PW, Pw, pW, and pw.

5. **Cross the Gametes**:
- The Punnett square will be a 4x4 grid since we are crossing two heterozygous plants.
- The resulting combinations will yield 16 different genotypes.

6. **Determine the Phenotypes**:
- According to the principle of complementary genes, the purple flower color will only appear if both dominant alleles (P and W) are present.
- If either allele is recessive (p or w), the flower color will be white.

7. **Calculate the Phenotypic Ratio**:
- The phenotypic ratio for this complementary gene interaction is 9:7.
- This means that out of 16 possible combinations, 9 will result in purple flowers and 7 will result in white flowers.

8. **Conclusion**:
- Therefore, the total number of phenotypes with respect to flower color is **2** (purple and white).

### Final Answer:
The number of phenotypes with respect to flower color possible when selfing a heterozygous Lathyrus odoratus for two loci is **2** (purple and white).

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