The output nexus file contains the SNP data in one of two forms, depending
upon what you regard as most appropriate. One form, that used by Chifman and
Kubatko, has two lines per individual, one providing the reference SNP the
second providing the alternate SNP (method=1).
A second form, recommended by Dave Swofford, has a single line per
individual, resolving heterozygous SNPs by replacing them with standard
ambiguity codes (method=2).
If the data are tag presence/absence, then method=2 is assumed.