Final answer:
MHC is said to be highly polymorphic due to the presence of multiple alleles for each gene coding for MHC in the population. This diversity is crucial for the immune system's ability to recognize a wide array of antigens and to distinguish self from non-self in the context of organ transplantation.
Step-by-step explanation:
The Major Histocompatibility Complex (MHC) is a collection of genes that code for proteins expressed on the surfaces of all nucleated cells. Due to the presence of a large number of alleles of each gene coding for MHC in the population, MHC is said to be highly polymorphic. This polymorphism, characterized by multiple alleles for each individual MHC locus, is a result of population genetics and is crucial in the immune system for the recognition and presentation of antigens to T cells. The highly polymorphic nature of the MHC ensures that each individual has a unique set of MHC molecules, which can be problematic during organ transplants, as the recipient's immune system may recognize the donor's MHC molecules as foreign and reject the transplant. The polygeny and polymorphism of the MHC contribute to the immune system's ability to respond to a wide variety of pathogens.