The most general format of locusAttributes a list of lists, one for each
marker, where possible entries in the inner lists are as follows (default
values in parenthesis):
alleles : a character vector with allele labels
afreq : a numeric vector with allele frequencies (rep.int(1/L, L),
where L = length(alleles))
chrom : chromosome number (NA)
posMb : physical location in megabases (NA)
name : marker name (NA)
mutmod : mutation model, or model name (NULL)
rate : mutation model parameter (NULL)
If locusAttributes is just a single list of attributes (not a list of
lists), then it is repeated to match the number of markers. In particular,
the shortcut locusAttributes = "snp-12" sets all markers to be SNPs with
alleles 1 and 2.`
Two alternative format of locusAttributes are allowed: If a data.frame or
matrix is given, an attempt is made to interpret it as a frequency database
in allelic ladder format. Such an interpretation is also attempted if
locusAttributes is a list of named frequency vectors (where the names are
the allele labels).