The phenotypic ratio in a back cross between a trihybrid and homozygous recessive parent would be :-

Options

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

Answer

To determine the phenotypic ratio in a back cross between a trihybrid and a homozygous recessive parent, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Terms**:
- A **trihybrid** refers to an organism that is heterozygous for three different traits (e.g., AaBbCc).
- A **homozygous recessive** parent would have the genotype for all three traits as recessive (e.g., aabbcc).

2. **Identify the Cross**:
- The back cross in this scenario is between a trihybrid (AaBbCc) and a homozygous recessive parent (aabbcc).

3. **Determine Gametes Produced**:
- The trihybrid parent can produce 8 different types of gametes due to independent assortment: ABC, ABc, AbC, Abc, aBC, aBc, abC, and abc.
- The homozygous recessive parent can only produce one type of gamete: abc.

4. **Set Up the Punnett Square**:
- Since the homozygous recessive parent can only produce one type of gamete, the Punnett square will have 8 rows (one for each gamete from the trihybrid).
- The resulting offspring will be a combination of the trihybrid gametes with the homozygous recessive gamete.

5. **Determine the Phenotypic Ratio**:
- Each offspring from the trihybrid will exhibit a phenotype based on the dominance of the alleles from the trihybrid.
- The phenotypic ratio from this back cross will be 1:1:1:1:1:1:1:1 (8 different phenotypes), corresponding to the 8 different combinations of traits.

6. **Conclusion**:
- Therefore, the phenotypic ratio in a back cross between a trihybrid and a homozygous recessive parent is **1:1:1:1:1:1:1:1**.

### Final Answer:
The phenotypic ratio in a back cross between a trihybrid and a homozygous recessive parent would be 1:1:1:1:1:1:1:1.

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