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 statement accurately describes Mendelian inheritance as typically involving traits that follow a simple dominant-recessive pattern, often represented with two alleles, while non-Mendelian inheritance can include multiple alleles (like in blood type) or more complex patterns like incomplete dominance, codominance, and polygenic inheritance.