Testcross is a cross between a) Hybrid x Dominant parent b) Hybrid x Recessive parent c) Hybrid x Hybrid parent d) Two distantly related species

Options

A. Hybrid x Dominant parent
B. Hybrid x Recessive parent
C. Hybrid x Hybrid parent
D. Two distantly related species

Answer

### Step-by-Step 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. It involves crossing the organism in question (the F1 hybrid) with a homozygous recessive individual.

2. **Identifying the Parents**: In a typical test cross, we consider two types of parents:
- One parent is the F1 hybrid (which can be either homozygous dominant or heterozygous).
- The other parent is a homozygous recessive individual.

3. **Purpose of Test Cross**: The main purpose of performing a test cross is to reveal whether the F1 hybrid is homozygous (AA) or heterozygous (Aa). This is done by observing the phenotypes of the offspring produced from the cross.

4. **Example of a Test Cross**:
- Let’s say we have a tall plant (dominant trait) represented by "A" and a dwarf plant (recessive trait) represented by "a".
- The F1 generation (resulting from crossing A and a) will all be tall (genotype could be either AA or Aa).
- To determine the genotype of the F1 hybrid, we perform a test cross by crossing it with a homozygous recessive plant (aa).

5. **Analyzing Offspring**:
- If the F1 hybrid is homozygous (AA), all offspring will be tall (genotype Aa).
- If the F1 hybrid is heterozygous (Aa), the offspring will show a 1:1 ratio of tall (Aa) to dwarf (aa) plants.

6. **Conclusion**: Since a test cross specifically involves crossing a hybrid with a recessive parent to determine the genotype of the hybrid, the correct answer to the question is **b) Hybrid x Recessive parent**.