The true statement is:
Mendelian inheritance concerns genetic traits that are controlled by only two alleles, while non-Mendelian inheritance is controlled by multiple alleles.
This is because Mendelian inheritance typically refers to inheritance patterns that follow the laws proposed by Gregor Mendel, often involving discrete traits influenced by single gene pairs (two alleles: one from each parent). Non-Mendelian inheritance includes patterns where traits are influenced by multiple alleles, polygenic traits, incomplete dominance, codominance, or other complex genetic interactions.