  We study the electronic properties of DNA by way of a tight-binding model
applied to four particular DNA sequences. The charge transfer properties are
presented in terms of localisation lengths, crudely speaking the length over
which electrons travel. Various types of disorder, including random potentials,
are employed to account for different real environments. We have performed
calculations on poly(dG)-poly(dC), telomeric-DNA, random-ATGC DNA and
lambda-DNA. We find that random and lambda-DNA have localisation lengths
allowing for electron motion among a few dozen base pairs only. A novel
enhancement of localisation lengths is observed at particular energies for an
increasing binary backbone disorder. We comment on the possible biological
relevance of sequence dependent charge transfer in DNA.
