What is MHC haplotype?
The particular combination of MHC alleles found on a single chromosome is known as an MHC haplotype. Expression of MHC alleles is codominant, with the protein products of both the alleles at a locus being expressed in the cell, and both gene products being able to present antigens to T cells (Fig. 5.13).
What is the difference between MHC-I and MHC II?
The main difference between MHC class 1 and 2 is that MHC class 1 molecules present antigens to cytotoxic T cells with CD8+ receptors whereas MHC class 2 molecules present antigens to helper T cells with CD4+ receptors.
Why is MHC polymorphic?
The variations in the MHC molecules (responsible for the polymorphism) are the result of the inheritance of different MHC molecules, and they are not induced by recombination, as it is the case for the antigen receptors.
What is HLA genotype?
HLA is the human version of the major histocompatibility complex (MHC), a gene family that occurs in many species. Genes in this complex are categorized into three basic groups: class I, class II, and class III. In humans, the HLA-B gene and two related genes, HLA-A and HLA-C, are the main genes in MHC class I.
Why are MHC polygenic and polymorphic?
First, the MHC is polygenic. It contains several different MHC-I and MHC-II genes so that every individual possesses a set of MHC molecules with different ranges of peptide-binding specificities. Second, the MHC is extremely polymorphic. The MHC genes display the greatest degree of polymorphism in the human genome.
How many haplotypes does a person have?
A haplotype is defined as the combination of alleles for different polymorphisms that occur on the same chromosome (189), and for any given stretch of chromosomal DNA an individual will have two haplotypes, although at a population level there may be numerous haplotypes for any given stretch of chromosomal DNA.
What are MHC I and MHC II proteins?
There are two major types of MHC protein molecules—class I and class II. Class I MHC molecules span the membrane of almost every cell in an organism, while class II molecules are restricted to cells of the immune system called macrophages and lymphocytes.
What is Y DNA haplogroup H?
For the human Y-DNA haplogroup, see Haplogroup H (Y-DNA). Haplogroup H is a human mitochondrial DNA (mtDNA) haplogroup. The clade is believed to have originated in Southwest Asia, near present day Syria, around 20,000 to 25,000 years ago.
What is the human mtDNA haplogroup?
This article is about the human mtDNA haplogroup. For the human Y-DNA haplogroup, see Haplogroup H (Y-DNA). Haplogroup H is a human mitochondrial DNA (mtDNA) haplogroup. The clade is believed to have originated in Southwest Asia, near present day Syria, around 20,000 to 25,000 years ago.
What is haplogroup H2a2a1?
Haplogroup H is a descendant of haplogroup HV. The Cambridge Reference Sequence (CRS), which until recently was the human mitochondrial sequence to which all others were compared, belongs to haplogroup H2a2a1 (human mitochondrial sequences should now be compared with the ancestral Reconstructed Sapiens Reference Sequence (RSRS)).
Where are haplogroups H18 and H20 found?
H18 occurs on the Arabian Peninsula. These haplogroups are both found in the Caucasus region. H20 also appears at low levels in the Iberian Peninsula (less than 1%), Arabian Peninsula (1%) and Near East (2%). These subclades are found mostly in Europe, South-West Asia and Central Asia.