Monohybrid test cross ratio is

Options

A. `1:1:1:1`
B. `1:1`
C. `9:3:4`
D. `9:3:3:1`

Answer

To solve the question regarding the monohybrid test cross ratio, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Monohybrid Cross**: A monohybrid cross involves one trait, which can be dominant or recessive. For example, let's consider the trait of plant height, where 'T' represents tall (dominant) and 't' represents dwarf (recessive).

2. **Identify Genotypes**: The tall plant can either be homozygous dominant (TT) or heterozygous (Tt). The dwarf plant will always be homozygous recessive (tt).

3. **Perform a Test Cross**: A test cross is performed by crossing the tall plant with the dwarf plant (tt) to determine the genotype of the tall plant.

4. **Analyze the Outcomes**:
- If the tall plant is homozygous dominant (TT):
- The offspring will all be tall (TT x tt → all Tt).
- If the tall plant is heterozygous (Tt):
- The offspring will have a 1:1 ratio of tall to dwarf plants (Tt x tt → 50% Tt (tall) and 50% tt (dwarf)).

5. **Determine the Test Cross Ratio**: The test cross ratio for a monohybrid cross is therefore:
- If homozygous dominant: all tall (1:0 ratio).
- If heterozygous: 1 tall : 1 dwarf (1:1 ratio).

6. **Conclusion**: The typical monohybrid test cross ratio is 1:1 when the tall plant is heterozygous.

### Final Answer:
The monohybrid test cross ratio is **1:1**.

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