chr2
Kinship matrices are calculated in a leave-one-out or leave-two-out manner, i.e. the chromosome(s) on which the markers being tested are located are left out of the kinship correction. This argument indicates the chromosome on which one marker of the marker pair resides. It indicates which kinship matrix to use for the data correction. If chr2 == chr1, the leave-one-out kinship matrix for that chromosome will be used. Otherwise, the leave-two-out kinship matrix is used. If both chr1 and chr2 are NULL, the kinship matrix for the entire genome will be used.