Which genotype ratio will appear by the trihybrid test cross in a completely linked plant :-

Options

A. `1 : 1 : 1 : 1 : 1 : 1 : 1 : 1`
B. `1 : 1 : 1 : 1`
C. `1 : 1`
D. `1 : 2 : 1`

Answer

To determine the genotype ratio that will appear from a trihybrid test cross in a completely linked plant, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Complete Linkage**:
- In a completely linked scenario, the genes are located very close to each other on the same chromosome. This means that they will not assort independently and will not undergo recombination during meiosis.

2. **Defining a Trihybrid Cross**:
- A trihybrid cross involves three different traits, each represented by two alleles. For example, let’s denote the three traits as A, B, and C, where A and a are one pair of alleles, B and b are another pair, and C and c are the third pair.

3. **Performing a Test Cross**:
- A test cross is performed between the F1 progeny (which is heterozygous for all three traits, i.e., AaBbCc) and a homozygous recessive individual (aabbcc).

4. **Determining Gametes from the F1**:
- Since the genes are completely linked, the F1 plant can only produce one type of gamete: ABC (dominant alleles) and abc (recessive alleles).

5. **Gametes from the Homozygous Recessive Parent**:
- The homozygous recessive parent (aabbcc) can only produce one type of gamete: abc.

6. **Combining Gametes**:
- When we combine the gametes from the F1 plant and the homozygous recessive parent, we get two possible combinations:
- ABC (from F1) with abc (from recessive parent) = AaBbCc (dominant phenotype)
- abc (from F1) with abc (from recessive parent) = aabbcc (recessive phenotype)

7. **Calculating the Genotype Ratio**:
- Since there are only two combinations of gametes, the resulting genotype ratio will be 1:1. This means:
- 1 AaBbCc (dominant phenotype)
- 1 aabbcc (recessive phenotype)

### Final Answer:
The genotype ratio that will appear from a trihybrid test cross in a completely linked plant is **1:1**.

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