The experimental procedure involved the following steps:
Step 1: Separation of the two strands in the DNA sample.
Step 2: Annealing of the previously separated strands.
Step 3: Treatment of the double-stranded DNA with a 3' - 5' exonuclease.
Based on the results obtained from agarose gel electrophoresis, it was observed that the DNA from Step 3 exhibited a size smaller than 1kb.
To explain this outcome, the most possible reason is that the DNA in sample S possesses certain characteristics which could be:
It is palindromic.
It contains sequence repeats.
It experiences sequence inversion.
Each strand within the DNA sample contains a self-complementary sequence.