In the first versions of Atlas, any comparison of a Null allele to expressed typing would immediately be graded as Mismatch.
The discrepancy between matching and scoring results was deemed confusing by end-users and has been resolved with a new and improved way of Null allele handling by Atlas.
Matching
Matching is performed at the P-group level by Atlas. If one position at a locus contains a Null allele, then only the P-group(s) of the expressed typing will be considered and the locus will be treated as homozygous for the expressing P-groups.
Example:
A*03:01,01:11N will be treated as A*03:01P,03:01P. Therefore, this typing would be assigned a match count of 2 when compared to another typing with the same pair of P-groups, such as A*03:01,03:01, A*03:20,03:112, and A*03:411,02:43N.
MAC Interpretation
Null alleles present in the decoded/expanded allele string of a MAC are not considered when matching or scoring.
To learn more about the technical handling of Null alleles by Atlas, please visit this link.
To learn more about Null allele treatment by Hap-E and Atlas and see example scenarios, please visit this table.