Test cross can not be performed in

Options

A. Neurospora
B. Man
C. Pea
D. Dogs

Answer

### Step-by-Step Solution

1. **Understanding Test Cross**: A test cross is a genetic cross performed to determine whether an individual with a dominant phenotype is homozygous or heterozygous for a particular trait. This is done by crossing the individual with a homozygous recessive individual.

2. **Identifying the Organisms**: The question asks which organism cannot undergo a test cross. We need to analyze the options provided to identify the organism that is haploid.

3. **Characteristics of Diploid and Haploid Organisms**:
- Diploid organisms have two alleles for each gene (one from each parent). In these organisms, a test cross can be performed to determine the genotype of an individual with a dominant phenotype.
- Haploid organisms have only one allele for each gene. In these organisms, there is no need for a test cross because there is no second allele to compare against.

4. **Examples of Organisms**:
- Common diploid organisms include humans, pea plants (Pisum sativum), and dogs.
- An example of a haploid organism is Neurospora, a type of fungus.

5. **Conclusion**: Since a test cross requires the presence of two alleles to determine the genotype of an organism, it cannot be performed in haploid organisms like Neurospora. Therefore, the correct answer is Neurospora.

### Final Answer
Test cross cannot be performed in **Neurospora**.

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