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

Options

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

Answer

To determine which crosses will produce a 1:1 phenotypic ratio, we need to analyze the genetic crosses provided in the options. Here’s a step-by-step solution:

### Step 1: Understand the 1:1 Phenotypic Ratio
A 1:1 phenotypic ratio occurs when two different phenotypes are produced in equal proportions. This typically happens in monohybrid or certain dihybrid crosses where one parent is homozygous for one trait and the other is heterozygous.

### Step 2: Analyze Each Cross
1. **First Cross**:
- If one parent produces 4 types of gametes and the other produces only 1 type, the resulting offspring will show multiple phenotypes, not a 1:1 ratio. Therefore, this cross does not produce a 1:1 ratio.

2. **Second Cross**:
- If one parent produces gametes (A B, a B) and the other parent produces (a b), we can set up a Punnett square:
- Parent 1: A B, a B
- Parent 2: a b
- The possible combinations would yield a 1:1 ratio of phenotypes. This cross is likely to produce a 1:1 ratio.

3. **Third Cross**:
- If both parents produce the same type of gametes, the offspring will have the same genotype and phenotype. Thus, this cross cannot produce a 1:1 ratio.

4. **Fourth Cross**:
- If the progeny are dihybrid (e.g., AaBb), the resulting phenotypic ratio will be more complex than 1:1. Therefore, this cross does not yield a 1:1 ratio.

### Step 3: Conclusion
After analyzing all the crosses, the second cross is the only one that produces a 1:1 phenotypic ratio.

### Final Answer:
**The correct answer is the second cross.**

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