MHC Genetics · Types of Genes Class i ABC Class ii D Class iii Encode second component of complement( C2)- classical pathway Factor B--alternate pathway Two forms; 4th complement components ( C4a C4b) BIOL 533 Lecture 7BIOL 533 14 Lecture 7 MHC Genetics • Types of Genes – Class I ABC – Class II D – Class III • Encode second component of complement (C2)— classical pathway • Factor B—alternate pathway • Two forms; 4th complement components (C4a C4b)