Which of the following crossess will produce 1 : 1 phenotypic ratio :-

Options

A. AaBb `×x` aabb
B. AaBB `×x` aaBB
C. aabb `×x` aabb
D. AABB `×x` aabb

Answer

To determine which of the given crosses will produce a 1:1 phenotypic ratio, we can analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding the 1:1 Phenotypic Ratio**:
- A 1:1 phenotypic ratio occurs when two different phenotypes are produced in equal proportions. This typically happens in a monohybrid cross involving a heterozygous and a homozygous recessive individual.

2. **Analyzing the First Option**:
- The cross is: **AaBb x aaBb**.
- Possible gametes from AaBb: AB, Ab, aB, ab (4 types).
- Possible gametes from aaBb: aB, ab (2 types).
- Total combinations: 4 (from AaBb) x 2 (from aaBb) = 8 combinations.
- This will not yield a 1:1 ratio.

3. **Analyzing the Second Option**:
- The cross is: **AaBB x aaBB**.
- Possible gametes from AaBB: AB (1 type).
- Possible gametes from aaBB: aB (1 type).
- Total combinations: 1 (from AaBB) x 1 (from aaBB) = 1 combination.
- This will yield a 1:1 ratio (AB : aB).

4. **Analyzing the Third Option**:
- The cross is: **aaBB x aaBB**.
- Possible gametes: Only one type, which is aB.
- Total combinations: 1 (from aaBB) x 1 (from aaBB) = 1 combination.
- This will not yield a 1:1 ratio, as there is only one phenotype.

5. **Analyzing the Fourth Option**:
- The cross is: **AaBb x AaBb**.
- Possible gametes from AaBb: AB, Ab, aB, ab (4 types).
- Total combinations: 4 x 4 = 16 combinations.
- This will not yield a 1:1 ratio.

### Conclusion:
The only cross that produces a 1:1 phenotypic ratio is **Option B: AaBB x aaBB**.