A list with each component being the data for one
individual, as produced by the cross() function. Those
results are a list with two components, corresponding to the
maternal and paternal chromosomes. The chromosomes are represented
as lists with two components: an integer vector of alleles in
chromosome intervals, and a numeric vector of locations of the
right-endpoints of those intervals; these two vectors should have
the same length.
If the input L is a vector, in order to simulate multiple
chromosomes at once, then the output will be a list with length
length(L), each component being a chromosome and having the
form described above.