Linkage of the four gamma subclass heavy chain genes.

Abstract
The genes for the heavy-chain constant regions of the 4 .gamma. subclass Ig were identified in a set of overlapping mouse DNA fragments representing .apprx. 100 kilobase pairs (kb) of the mouse genome that was cloned from bacteriophage .lambda. libraries of BALB/c mouse embryo DNA. R-loop mapping studies show that the genes are located 5''-C.gamma.3-34 kb-C.gamma.1-21 kb-C.gamma.2b-15 kb-C.gamma.2a-3'' and lie in the same transcriptional orientation. Two DNA segments, one of 19 kb and another of 15 kb, that surround the C.gamma.2b and C.gamma.2a genes, respectively, show considerably homology and implicate a tandem duplication mechanism in the evolution of this gene cluster.