The serotype is determined by the antibody recognition of α25 subset of HLA-A α-chains.

A25 is believed to have been formed by a single gene conversion between another HLA-A and the A*2601 allele.[2].

A25 reasonably good serotyping with no overt false recognition.. A*2501 distribution is primarily located in Western Eurasia.

Frequency tends to be highest in the populations that underwent later neolithization suggesting A*2501 spread in Europe.

The high frequency in Saudi Arabia is suggestive of a source.