The format is:
List of 10
$ geno : num [1:150, 1:67] 1 2 1 1 2 1 2 1 1 2 ...
..- attr(*, "dimnames")=List of 2
.. ..$ : chr [1:150] "ID1" "ID2" "ID3" "ID4" ...
.. ..$ : chr [1:67] "M1" "M2" "M3" "M4" ...
$ n.ind : int 150
$ n.mar : int 67
$ segr.type : chr [1:67] "A.H" "A.H" "A.H" "A.H" ...
$ segr.type.num: logi [1:67] NA NA NA NA NA NA ...
$ n.phe : int 1
$ pheno : num [1:150, 1] 40.8 39.5 37.9 34.2 38.9 ...
..- attr(*, "dimnames")=List of 2
.. ..$ : NULL
.. ..$ : chr "Trait_1"
$ CHROM : NULL
$ POS : NULL
$ input : chr "onemap_example_bc.raw"
- attr(*, "class")= chr [1:2] "onemap" "backcross"