Result of test cross is

Options

A. all dominants phenotypes
B. 50% dominant and 50% recessive phenotypes
C. equal number of gentoypes and phenotypes in progeny
D. more than one option is correct

Answer

### Step-by-Step Solution:

1. **Understanding Test Cross**: A test cross is a genetic cross performed to determine the genotype of an individual with a dominant phenotype. This is done by crossing the individual with a homozygous recessive individual.

2. **Example of Mono-hybrid Cross**: Let's consider a simple example using pea plants where we observe the trait of height. Tallness (T) is dominant over dwarfness (t).

3. **Initial Cross**: When a pure tall plant (TT) is crossed with a pure dwarf plant (tt), all offspring (F1 generation) will be tall (Tt) due to the dominance of the tall allele.

4. **F1 Generation**: The F1 generation consists of heterozygous tall plants (Tt). However, we cannot determine whether these plants are homozygous (TT) or heterozygous (Tt) just by observing their phenotype.

5. **Conducting a Test Cross**: To determine the genotype of the tall plants, we perform a test cross by mating the tall plant (Tt or TT) with a homozygous recessive plant (tt).

6. **Possible Outcomes**:
- If the tall plant is homozygous (TT), all offspring will be tall (Tt).
- If the tall plant is heterozygous (Tt), the offspring will be a mix: 50% tall (Tt) and 50% dwarf (tt).

7. **Analyzing Results**:
- In the first case (TT), all offspring show the dominant phenotype (tall).
- In the second case (Tt), there will be both tall and dwarf offspring, indicating the parent was heterozygous.

8. **Conclusion**: The results of a test cross can show:
- All offspring are dominant phenotypes if the parent is homozygous.
- A 1:1 ratio of dominant to recessive phenotypes if the parent is heterozygous.

9. **Final Answer**: Since both scenarios can occur, the correct answer to the question "Result of test cross is" is that more than one option is correct.