makes a two-column matrix for subscripting alleles out of a genotype matrix

This is intended to be applied to a grouped tibble that has all the columns that are arguments to the function.

make_subscript_matrix(n, chrom, start, end, abs_column, m_list, num_markers)

Arguments

n

the number of rows in the group of the tibble

chrom

chromosome names

start

starting position of the segment

end

ending position of th segment

abs_column

the absolute column index of the founder

m_list

a list column of markers

num_markers

the number of markers