Test cross in plants or in Drosophila involves crossing

Options

A. Between two genotypes with recessive trait
B. Betwee two `F_(1)` hybrids
C. The `F_(1)` hybrid with a double recessive genotype
D. Between two genotypes with dominant trait

Answer

### Step-by-Step Text Solution:

1. **Understanding Test Cross**: A test cross is a genetic cross used to determine the genotype of an organism that exhibits a dominant phenotype. The organism in question could either be homozygous dominant (having two dominant alleles) or heterozygous (having one dominant and one recessive allele).

2. **Identifying the Cross**: In a test cross, the organism with the dominant phenotype is crossed with an individual that has a homozygous recessive genotype. This means that the recessive individual has two copies of the recessive allele.

3. **Purpose of the Test Cross**: The purpose of this cross is to observe the phenotypes of the offspring. If any offspring display the recessive phenotype, it indicates that the dominant phenotype parent is heterozygous. If all offspring display the dominant phenotype, the parent is homozygous dominant.

4. **Example**: For instance, if we consider a trait where "T" represents tall (dominant) and "t" represents short (recessive), we can have:
- Homozygous dominant: TT (tall)
- Heterozygous: Tt (tall)
- Homozygous recessive: tt (short)

If we perform a test cross of a tall plant (unknown genotype) with a short plant (tt), we can determine the genotype of the tall plant based on the offspring's phenotypes.

5. **Conclusion**: Therefore, the correct answer to the question is that a test cross in plants or in Drosophila involves crossing the F1 hybrid with a double recessive genotype.

### Final Answer:
The correct option is: **C. The F1 hybrid with a double recessive genotype.**

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