DNA loss during C-banding of chromosomes of Lilium longiflorum

Root tip chromosomes were uniformly labelled with ³H-thymidine and replicate squashes were made. One set was untreated, one incubated in Ba(OH)₂ solution, and a further set treated sequentially in Ba(OH)₂ and hot saline-citrate (2 × SSC) to reveal C-bands. All replicates were autoradiographed and comparative grain counts made. Differences in grain numbers per metaphase cell showed that Ba(OH)₂ extracted 40% of label, and that a further 23% was lost in the subsequent SSC incubation. The distribution of grains was mapped along a sample of each of five individually-recognisable chromosomes at the three treatment stages. Within each chromosome, the number of grains per segment did not differ significantly from a random distribution. This was true for all five chromosomes at all three stages of treatment, whether or not the regions were C-banded. - We conclude that DNA extraction occurs progressively during C-banding in Lilium, but that C-bands are not dark because of their relatively high retention of DNA.