What is MHC haplotype?

Question

What is MHC haplotype? I did check out the wiki article, but did not understand.

(I have not studied biology since last 8 years and now I am going through it because I need it for my research. So if someone can describe it in simple language it would be very helpful)

Answer 1

A haplotype is commonly defined as

...a group of genes within an organism that was inherited together from a single parent. -- Nature Scitable

This definition of haplotype applies whether it is just a few genes or all of the genes on an entire chromosome$^1$. In the case of the major histocompatibility complex, it is a group of more than 200 genes on chromosome 6 (Janeway et al. 2001). The set of alleles$^1$ inherited together from one parent form the MHC haplotype. Thus, one offspring will inherit two different MHC haplotypes, one from each parent. The different haplotypes with so many genes helps keep genetic variation in the overall complex, which improves the immune response ability of the organism.

The term is derived from haploid, which means half of the normal set of chromosomes. Humans for example are diploid, meaning it has two copies of each chromosome, one inherited from the mother (maternal) and one inherited from the father (paternal). So, when you inherit just one half of the crhomosome pair, you are inheriting a haplotype.

For general reference, it's important to note that haplotype was not always used to reference a group of two or more genes inherited together. It was commonly used to as a term to represent a sequence of nucleotides together on the same chromosome, even if only part of a single gene. For example, Bowen et al. (1995) used mitochondrial haplotypes to study the migration of loggerhead turtles across the Pacific Ocean. They used 350 nucleotides of the mitochondrial control region. The control region is over 1000 nucleotides in size but Bowen and colleagues only used 350 nucleotides from part of the control region. This use was very common in the 1990s and early 2000s before it became easier and less expensive to sequence entire genomes, or at least many genes.

Citaton

Bowen, B.W. et al. 1995. Trans-Pacific migrations of the loggerhead turtle (*Caretta caretta) demonstrated with mitochondrial DNA markers. Proceedings of the National Academy of Sciences USA 92: 3731-3734.

Janeway, Jr., C.A. et al. 2001. Immunobiology, 5th edition. Garland Science, New York.

Footnote

1. More accurately, it would be the set of alleles at each gene locus (gene location) inherited together. The same genes are inherited from either parent, but the alleles (variations of the gene) may be different between the two parents.

Answer 2

As stated in wiki "The major histocompatibility complex (MHC) is a set of cell surface molecules encoded by a large gene family in all vertebrates which controls a major part of the immune system. MHC molecules mediate interactions of leukocytes, also called white blood cells (WBCs), which are immune cells, with other leukocytes or with body cells. MHC determines compatibility of donors for organ transplant as well as one's susceptibility to an autoimmune disease via crossreacting immunization. In humans, MHC is also called human leukocyte antigen (HLA)."

Basically, MHC control immune system and it work based on principle lock and key. MHC has specific cell surface that can bind to foreign materials that have compatible binding site and recognise it as pathogen or harmful compound.