In H2b and H2s haplotype strains (e.g. C57BL/6, C57BL/10, C57L/J, LP/J, 129 and SJL/J mice), there is a deletion of 627 bp in the promoter and the first exon, leading to a failure to express the gene. In the haplotype H2q gene, an insertion in the second exon results in a frameshift and a premature stop codon, and in the haplotype H2f gene, a base substitution creates a stop codon in the first exon, leading to defective protein translation in the strains of these haplotypes. Belongs to the MHC class II family. Defined as a polymorphic pseudogene by MGI.