Excluded Volume Effects in Gene Stretching

We investigate the effects excluded volume on the stretching of a single DNA in solution. We find that for small force F, the extension h is not linear in F but proportion to F^{\chi}, with \chi=(1-\nu)/\nu, where \nu is the well-known universal correlation length exponent. A freely joint chain model with the segment length chosen to reproduce the small extension behavior gives excellent fit to the experimental data of \lambda-Phage DNA over the whole experimental range. We show that excluded volume effects are stronger in two dimensions and also derive results in two dimensions which are different from the three dimensional results. This suggests experiments to be performed in these lower dimensions.