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.
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   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.