- Gregor Mendel studied inheritance through experiments with pea plants and discovered that traits are passed from parents to offspring through discrete units called genes. - Mendel observed that traits can be dominant or recessive, and used mathematical probabilities to predict inheritance patterns in subsequent generations. - The concept of codominance was later introduced, where both alleles of a gene are expressed equally in heterozygotes rather than one being dominant. Blood type inheritance in humans follows codominance.