Mendel did not notice/ An exception to Mendel's laws:

Options

A. Dominance
B. Purity of gametes/segeration
C. Linkage
D. Independent assortment.

Answer

### Step-by-Step Solution:

1. **Understanding Mendel's Laws**: Mendel proposed several laws of inheritance, including the law of dominance, the law of segregation, and the law of independent assortment. Each of these laws describes how traits are inherited from one generation to the next.

2. **Analyzing the Options**:
- **Option 1: Dominance**: This principle states that when two contrasting alleles are present, one will be dominant and expressed, while the other will be recessive and not expressed. This is a fundamental aspect of Mendel's laws, so it is not an exception.

- **Option 2: Purity of Gametes and Segregation**: This principle states that during gamete formation, alleles segregate so that each gamete carries only one allele for each character. This is also a key part of Mendel's laws and not an exception.

- **Option 3: Linkage**: Linkage refers to the physical association of genes located on the same chromosome. This phenomenon can lead to the inheritance of traits together, which contradicts Mendel's law of independent assortment. Therefore, linkage is an exception to Mendel's laws.

- **Option 4: Independent Assortment**: This law states that the inheritance of one trait is independent of the inheritance of another trait. This is another fundamental principle of Mendelian genetics, so it is not an exception.

3. **Conclusion**: Based on the analysis of the options, the correct answer is **linkage** (Option 3), as it represents an exception to Mendel's laws of inheritance.