Histocompatibility (tissue testing)

Histocompatibility is determined by what are called major histocompatibility complex (MHC). These are genes that are carried on chromosome 6 and their present designation is 6p 2,1-6p2,3. Gene loci are labeled A, B, C, D. The loci are called haplotypes because they are inherited in block with minimal cross over. The alleles or specificities at each locus are identified by numbers 1, 2, 3 etc. If the specificity is provisional, it is designated W for workshop. There are 20 specificities on loci A, B and C and 6 on D. Inheritance of tissue types is just as simple as the inheritance of blood groups except for genetic linkage which occurs in 15 of cases. The particular combination of specificities on the same chromosomes is called the haplotype. 90% of people are heretozygous with two different alleles at each locus.

Hence we have MCH which are inherited as haplotypes with loci (AB C D ) which have the following specificities 1,2,3, 4 etc

The genes express what are called HLA antigens


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