The value of maxna
can be either less than one, or greater or
equal to one. In the former case, it is taken as specifying the
maximum proportion (relative frequency) of missing data within a given
haplotype. In the latter case, it is taken as the maximum number
(absolute frequency).
na = "all"
is a shortcut for all ambiguous nucleotides
(including N) plus alignment gaps and completely unknown site (?).
na = "ambiguous"
is a shortcut for only ambiguous nucleotides
(including N).