Major histocompatibility complex
Major histocompatibility complex (MHC) or, in humans, human leukocyte antigen (HLA) produces proteins that are essential for immune system functioning. The genes of the MHC complex have extremely high variability, assumed to be a result of frequency-dependent parasite-driven selection and mate choice. This is believed to be so it promotes heterozygosity improving the chances of survival for the offspring.