If, for instance, subject has in his genome IGHV1-2*02 and a novel
allele equally close to IGHV1-2*02 and IGHV1-2*05, the novel allele may be
detected by analyzing sequences that best align to either of these alleles.
If keep_alleles is TRUE, both polymorphic allele calls will
be retained. In the case that multiple mutation ranges are checked for the
same allele, only one mutation range will be kept in the output.