The recombination frequencies between 3 gene pairs
(b-cn 9%, cn-vg 9.5%, and b-vg 17%)
best fit a linear order in which cn is positioned about halfway between
the other 2 genes.
Recombination frequencies can be used to construct a linkage map
of the chromosome, since the farther apart genes are, the more
likely they are to be separated during crossing over, and the higher
their frequency of recombination.