Final answer:
MHC genes are expressed co-dominantly, with alleles from both parents contributing equally to the phenotype, and the MHC loci are highly polymorphic, enhancing immune system diversity.
Step-by-step explanation:
The MHC genes (Major Histocompatibility Complex) are expressed in a co-dominant fashion. This means that each allele (variant of a gene) contributes to the phenotype. In the context of MHC genes, which are crucial for the immune system, the alleles inherited from both parents are expressed equally, providing a greater diversity of immune response. The genetic loci that make up the MHC are highly polymorphic, meaning there is a high degree of variation within the MHC genes in the population. This polymorphism is beneficial because it increases the likelihood that some individuals in the population can effectively present any given pathogen-derived peptide and thus mount an effective immune response.