The immunoglobulin lambda variable light-chain region in primates has been shaped by multiple, independent, small-scale and large-scale insertion/deletion events.
We analyzed genomes of nonhuman primates to determine the ancestral state of a 9.1-kb insertion/deletion polymorphism, located on human chromosome 22. The 9.1-kb+ allele was found in 16 chimpanzees, 3 bonobos, and 2 Bornean orangutans; however, 9 chimpanzees and 6 Sumatran orangutans showed neither the 9.1-kb+ nor the 9.1-kb- allele, but a novel allele, termed 9.1-kbnull. A clone from a chimpanzee BAC library carrying the 9.1-kbnull allele was sequenced: the BAC DNA aligns with the human chromosome 22 reference sequence except for a 75-kb region, suggesting that the 9.1-kbnull allele originated from a deletion. Furthermore, the 9.1-kb+ chromosomes of chimpanzees and bonobos contain a 1030-nucleotide sequence, absent in humans, that may result from a retro-transposition insertion in their common ancestor. Our results provide additional evidence that human chromosome 22 has undergone multiple small-scale and large-scale insertions and deletions since sharing a common ancestor with other primates.