In Lathyrus odoratus gene A and B are essential in dominant form to produce purple colour then which of the following cross produce only coloured offspringI
I. Aa Bb x aa bb
II. aa BB x AA bb
III. AA BB X aa bb
IV. aa BB x aa Bb

Options

A. I and IV
B. I and II
C. Only l
D. II and III

Answer

To determine which crosses produce only colored offspring in Lathyrus odoratus, we need to analyze each cross based on the requirement that both dominant alleles (A and B) must be present for the purple color to appear. Let's evaluate each cross step by step.

### Step-by-Step Solution:

1. **Understanding the Requirement**:
- For a plant to produce purple flowers, it must have at least one dominant allele of gene A (A) and one dominant allele of gene B (B).
- Therefore, the genotypes that will produce purple flowers are:
- AABB, AABb, AaBB, AaBb.

2. **Analyzing Each Cross**:
- **Cross I: Aa Bb x aa bb**
- Gametes from Aa Bb: AB, Ab, aB, ab
- Gametes from aa bb: ab
- Possible offspring:
- AaBb (purple), Aabb (not purple), aaBb (not purple), aabb (not purple).
- Result: Only 1 out of 4 is purple. **Not all offspring are colored.**

- **Cross II: aa BB x AA bb**
- Gametes from aa BB: aB
- Gametes from AA bb: AB, Ab
- Possible offspring:
- AaBb (purple), Aabb (not purple).
- Result: Only 1 out of 2 is purple. **Not all offspring are colored.**

- **Cross III: AA BB x aa bb**
- Gametes from AA BB: AB
- Gametes from aa bb: ab
- Possible offspring:
- AaBb (purple).
- Result: All offspring are purple. **All offspring are colored.**

- **Cross IV: aa BB x aa Bb**
- Gametes from aa BB: aB
- Gametes from aa Bb: aB, ab
- Possible offspring:
- aaBB (not purple), aaBb (purple).
- Result: Only 1 out of 2 is purple. **Not all offspring are colored.**

3. **Conclusion**:
- The only cross that produces only colored offspring is **Cross III: AA BB x aa bb**.

### Final Answer:
The cross that produces only colored offspring is **III. AA BB x aa bb**.