data
2 column matrix of allele counts, with each row as a SNP. Columns 1 and 2 refer to the 2 haplotypes. Each entry is either 1, 0 or NA.
chr
Vector of chromosome identifiers, one for each SNP. Each entry is an integer, 1-22 for the autosomes. If two X chromosomes for a female are being analysed, it should be identified by the number 23.