A three-point mapping cross involving the
brown midrib (bm),
virescent seedling (v), and
purple aleurone (pr)
genes in maize.
Following a DCO in a three-point mapping cross,
the allele in the middle position will be flanked by the other two alleles.
So a pr–v–bm sequence will show
pr+–v–bm+ after a DCO (least frequent)
event. This is notobserved.