Our adaptive immune systems are able to produce antibodies against billions of potential germs, but we only have a relative handful of genes that encode antibodies. These presented a paradox that was solved by Susumu Tonegawa, who discovered that our B and T cells edit their genomes to shuffle together different antibody subunit genes to create 3×1011 possible antibodies. IGK@ is one of the special places in the genome where this shuffling happens.
The systems for immune gene recombination are shared among jawed vertebrates, but the process happens differently in different species.
Click here to see the sequence of Day 40, jumping to a typical IGK@ gene, IGKV1-17.