Final answer:
HLAs that code for MHC-I molecules are HLA-A, HLA-B, and HLA-C, and they are highly polymorphic with thousands of alleles. MHC-I molecules are important for immune system functioning by presenting peptides to T cells.
Step-by-step explanation:
The HLAs (Human Leukocyte Antigens) that code for MHC-I (major histocompatibility complex class I molecules) include HLA-A, HLA-B, and HLA-C. These genes are highly polymorphic, which means they have a high number of alleles; there are 1,527 alleles for HLA-A, 2,110 for HLA-B, and 1,200 for HLA-C, contributing to a vast diversity in MHC-I molecules.
These MHC-I molecules are expressed on the surface of all nucleated cells, playing a critical role in the immune system by presenting peptides to T cells, which allows the immune system to detect and respond to pathogens or diseased cells.