Mhc is an extended cluster of genes with extraordinary polymorphism , which consists of three classes of genes ( class i , class ii and classiii ) . they are different from each other in their structure , expression , mode of evolution and so on . class ii genes are further divided into two subclasses and the mhc genes spread over nearly all vertebrates extensively Mhc基因是一個高度多態(tài)的基因群,主要包括三大類基因?類( class ) 、類( class )和類( class )基因,它們無論在結(jié)構(gòu)組成、表達組織的類型、刺激特定t細胞的類群及長期進化等方面都有所不同;類基因還可進一步分為a 、 b兩個亞類:各類基因廣泛分布于各種脊椎動物體內(nèi)。