Test cross in plants or in Drosophila involves crossing:

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding Test Cross**: A test cross is a genetic cross used to determine the genotype of an organism showing a dominant phenotype. It involves crossing the organism with a homozygous recessive individual.

2. **Example Setup**: Consider a plant with a dominant trait (e.g., tallness) represented by the allele "T" and a recessive trait (e.g., shortness) represented by the allele "t". The homozygous dominant genotype would be "TT" and the homozygous recessive genotype would be "tt".

3. **Crossing Homozygous Parents**: When you cross a homozygous tall plant (TT) with a homozygous short plant (tt), all offspring (F1 generation) will be heterozygous (Tt) and exhibit the dominant phenotype (tall).

4. **Performing the Test Cross**: To determine whether the tall F1 hybrid (Tt) is homozygous (TT) or heterozygous (Tt), you perform a test cross by crossing it with a homozygous recessive individual (tt).

5. **Analyzing Offspring**: The possible offspring from this test cross will be:
- If the F1 hybrid is homozygous (TT), all offspring will be tall (TT).
- If the F1 hybrid is heterozygous (Tt), the offspring will be in a 1:1 ratio of tall (Tt) to short (tt).

6. **Conclusion**: The phenotypic ratio of the offspring from the test cross will indicate the genotype of the F1 hybrid. A 1:1 ratio of tall to short plants suggests that the F1 hybrid is heterozygous (Tt), while all tall offspring would indicate that it is homozygous (TT).