Final answer:
Chromosomes in the MHC region encode MHC class I and class II molecules, but β2-microglobulin and the invariant chain genes are not part of the MHC region.
Step-by-step explanation:
Chromosomes in the Major Histocompatibility Complex (MHC) region contain genes that encode MHC class I and class II molecules, but β2-microglobulin and the invariant chain genes are not part of the MHC region.
MHC class I molecules are composed of a longer α protein chain coupled with a smaller β₂ microglobulin protein, while MHC class II molecules are composed of two protein chains - an α chain and a β chain.
The antigen-binding cleft for MHC class I is formed by the α₁ and α2 domains, while for MHC class II, the cleft is formed by the α₁ and β₁ domains.