Techniques and high resolution DNA size markers for pulsed field gel electrophoresis

High resolution DNA size markers are described for pulsed field gel electrophoresis (PFGE). These markers provide resolution of 10-20 kbp over a size range from 10 kbp to more than 400 kbp and are produced by partial restriction digestion of lambda phage DNA concatemers (lambda ladder). High resolution markers extending to over 400 kbp are made by partial restriction digestion of lambda ladder embedded in agarose. Detailed methods are described for marker production and for DNA separation by contour-clamped homogeneous electric field (CHEF) electrophoresis. These markers and methods are useful for a variety of high resolution DNA mapping by PFGE.