Mendelian Traits: Monogenic Inheritance
Mendelian traits adhere to the principle of monogenic inheritance, where a single gene is responsible for a specific trait. These traits are typically discrete, such as eye color, and follow predictable inheritance patterns. Dominant alleles express their trait even when paired with a recessive allele, while recessive alleles require two copies to be visible.
Non-Mendelian Traits
While some Mendelian traits exist, many human traits exhibit non-Mendelian inheritance. Incomplete dominance occurs when both dominant and recessive alleles are expressed, resulting in an intermediate phenotype. Codominance occurs when both alleles are expressed fully. Genetic linkage, environmental influences, and contributions from multiple genes can also affect trait expression.
Significance of Mendelian Traits
Mendelian traits have historically been used to understand genetic principles and diagnose medical conditions. The Online Mendelian Inheritance in Man (OMIM) database catalogs human genotype-phenotype relationships. Certain highly heritable Mendelian traits were previously used as genetic markers in legal cases to establish paternity.
Examples of Mendelian Traits in Humans
While Mendelian inheritance patterns are less common in nature, some notable examples in humans include:
- Eye color: Brown eyes are dominant over blue eyes.
- Blood type: The ABO blood group system follows Mendelian inheritance.
- Phenylketonuria (PKU): A recessive disorder caused by a mutation in the enzyme that metabolizes phenylalanine.
- Achondroplasia: A dominant disorder that causes dwarfism.
Limitations of Mendelian Traits
It's important to note that most human traits do not follow strict Mendelian inheritance patterns. The human genome is complex and influenced by multiple factors, including genetic interactions and environmental influences. However, Mendelian traits provide a foundation for understanding genetic inheritance and contribute to the study of human health and genetic disorders.