A data frame with five columns: individual ID, mother ID,
father ID, sex, and generation. Founders have 0 for mother
and father ID. Sex is coded 0 for female and 1 for male.
Arguments
ngen
Number of generations of inbreeding
selfing
If TRUE, use selfing
parents
Vector of the parents' IDs. Should be integers, and
length must be a power of 2 (i.e., 2, 4, 8, ...)
firstind
Positive integer to assign to the first child. Must
be greater than max(parents).