Mendelian traits are characteristics determined by a single gene, following the principles of inheritance first described by Gregor Mendel. These principles include segregation (each parent contributes one allele to the offspring) and independent assortment (alleles for different genes segregate independently). Mendelian traits typically exhibit clear-cut phenotypic categories, such as attached or unattached earlobes, or specific blood types. They are often studied using pedigree analysis to track their inheritance patterns across generations, revealing dominant, recessive, or co-dominant expression.

Non-Mendelian traits, in contrast, do not follow these simple inheritance patterns. They are often more complex, influenced by multiple genes (polygenic inheritance), environmental factors, or a combination of both. Examples include height, skin color, intelligence, and many common diseases like heart disease or diabetes. These traits often show a continuous range of variation rather than distinct categories. Other forms of non-Mendelian inheritance include incomplete dominance (where heterozygotes show an intermediate phenotype), co-dominance (where both alleles are expressed equally), multiple alleles (more than two alleles for a single gene), pleiotropy (one gene affecting multiple traits), epistasis (one gene masking or modifying the expression of another), and mitochondrial inheritance (traits passed down only from the mother). Understanding both Mendelian and non-Mendelian traits is crucial for comprehending the full spectrum of genetic inheritance and its role in human variation and disease.