Changes

===MHC Polymorphism In People===

===MHC Polymorphism In People===

* There are three types (loci) of MHC class I molecules known as human leukocyte antigen (HLA)- A, B, and C

* There are three types (loci) of MHC class I molecules known as human leukocyte antigen (HLA) - A, B, and C

* Equally there are three loci of MHC class II molecules - HLAs DP, DQ and DR

* Equally there are three loci of MHC class II molecules - HLAs DP, DQ and DR

In the entire human population there are only approximately 50 different variants (alleles) at each MHC class I and class II locus.

In the entire human population there are only approximately 50 different variants (alleles) at each MHC class I and class II locus.

The variation within MHC class I is entirely based on the class I heavy chain (the β2m is invariant). The variation within MHC class II is mainly within the β chains. Every individual has two alleles at each MHC locus inherited one from each parent. Any individual will therefore express two variants at most at each locus.

The variation within MHC class I is entirely based on the class I heavy chain (the β2m is invariant). The variation within MHC class II is mainly within the β chains. Every individual has two alleles at each MHC locus inherited one from each parent. Any individual will therefore express two variants at most at each locus.

This gives a maximum variability for an individual of:

This gives a maximum variability for an individual of:

* 6 different variants of MHC class I (2 each of HLA- A, B and C)

* 6 different variants of MHC class I (2 each of HLA - A, B and C)

* 6 different variants of MHC class II (2 each of HLA- DP, DQ and DR)

* 6 different variants of MHC class II (2 each of HLA - DP, DQ and DR)

Many animal species have fewer loci than the human e.g. ruminants have no MHC class II DP.

Many animal species have fewer loci than the human e.g. ruminants have no MHC class II DP.