¥ DNA/RNA from a biological source are usually inserted into a
cloning vector (e.g. Plasmid or phage) so that they can be cloned.
¥ Sequencing of such constructs frequently produces raw sequences
that include segments derived from vectors.
¥ Also transposable elements from the cloning host (generally
bacteria or yeast) can insert into the cloned DNA/RNA while the clone is being
propagated and will then be sequenced, as can DNA/RNA contaminants.