Select the incorrect statement .

Options

A. Linkage is inversely proportional to independent assortment .
B. Persons affected by PKU do not show mental disorders.
C. The `F_2` phenotypic and genotypic ratio is the same in incomplete dominance.
D. In dihybrid, cross each character inheritance resemble a monohybrid cross.

Answer

To solve the question of selecting the incorrect statement, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Linkage and Independent Assortment**:
- The first statement claims that "linkage is inversely proportional to independent assortment." This is a correct statement. Linkage refers to genes that are located close together on the same chromosome and tend to be inherited together, while independent assortment refers to the random distribution of alleles during gamete formation. Thus, the closer the genes are (more linkage), the less likely they will assort independently.

**Hint**: Remember that linkage affects how genes are inherited together, while independent assortment relates to how they segregate during gamete formation.

2. **Phenylketonuria (PKU) and Mental Disorders**:
- The second statement states that "persons affected by PKU do not show mental disorder." This statement is incorrect. PKU (Phenylketonuria) is a genetic disorder that can lead to severe mental retardation if not treated properly. Individuals with PKU must adhere to a strict diet to prevent the accumulation of phenylalanine, which can cause brain damage.

**Hint**: Consider the consequences of untreated genetic disorders and their impact on mental health.

3. **F2 Phenotypic and Genotypic Ratios in Incomplete Dominance**:
- The third statement asserts that "the F2 phenotype and genotypic ratio is the same in incomplete dominance." This statement is correct. In incomplete dominance, the F2 generation typically shows a phenotypic ratio of 1:2:1, which is the same as the genotypic ratio.

**Hint**: Recall that incomplete dominance results in a blending of traits, leading to distinct phenotypes.

4. **Dihybrid Cross and Monohybrid Cross Resemblance**:
- The fourth statement claims that "in a dihybrid cross, each character's inheritance resembles a monohybrid cross." This statement is also correct. In a dihybrid cross, while two traits are being studied, each trait can still segregate independently, similar to a monohybrid cross.

**Hint**: Think about how traits are inherited separately in dihybrid crosses, akin to monohybrid crosses.

### Conclusion:
After analyzing all the statements, the incorrect statement is the second one: "persons affected by PKU do not show mental disorder."

### Final Answer:
The incorrect statement is the second one regarding PKU.