An exception to the law of independent assortment is :-

Options

A. Dominance
B. Incomplete dominance
C. Segregation
D. Linkage

Answer

**Step-by-Step Solution:**

1. **Understand the Law of Independent Assortment**: This law states that alleles for different traits segregate independently of one another during gamete formation. This means that the inheritance of one trait does not affect the inheritance of another trait.

2. **Identify the Dihybrid Cross**: The law of independent assortment is typically illustrated using a dihybrid cross, which involves two traits. For example, if we consider seed shape (round vs. wrinkled) and seed color (yellow vs. green), the expected phenotypic ratio in the offspring would be 9:3:3:1.

3. **Recognize Exceptions to the Law**: While the law of independent assortment holds true under many circumstances, there are exceptions. One significant exception is the phenomenon known as "linkage."

4. **Define Linkage**: Linkage occurs when two genes are located close to each other on the same chromosome. Because of their proximity, they tend to be inherited together during meiosis, which means they do not assort independently.

5. **Impact of Linkage on Inheritance Ratios**: When genes are linked, the expected 9:3:3:1 ratio from a dihybrid cross is altered. Instead, a different ratio such as 1:1:1:1 may be observed, depending on the specific traits being studied.

6. **Conclude the Answer**: Therefore, the exception to the law of independent assortment is linkage, which disrupts the independent segregation of genes.

**Final Answer**: The exception to the law of independent assortment is linkage.

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