A test cross distinguishes between :

Options

A. two homozygous forms
B. a homozygous dominant and a heterozygous form
C. a homozygous recessive and a heterozygous form
D. two heterozygous forms

Explanation

To solve the question "A test cross distinguishes between:", we will follow these steps:

### Step-by-Step Solution:

1. **Understanding the Test Cross**:
- A test cross is a genetic cross performed to determine the genotype of an individual that exhibits a dominant phenotype. The individual in question could either be homozygous dominant (AA) or heterozygous (Aa).

2. **Identifying the Recessive Parent**:
- In a test cross, the individual with the dominant phenotype is crossed with a homozygous recessive individual (aa). This is crucial because the recessive phenotype will only show if the individual is homozygous recessive.

3. **Analyzing the Offspring Ratios**:
- The offspring from this cross will help us determine the genotype of the dominant phenotype parent.
- If the dominant phenotype parent is homozygous dominant (AA), all offspring will show the dominant phenotype (100% dominant).
- If the dominant phenotype parent is heterozygous (Aa), the offspring will show a 1:1 ratio of dominant to recessive phenotypes (50% dominant and 50% recessive).

4. **Conclusion**:
- Therefore, the test cross is used to distinguish between a homozygous dominant genotype and a heterozygous genotype based on the phenotypic ratios of the offspring produced.

### Final Answer:
A test cross distinguishes between homozygous dominant and heterozygous genotypes.

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