3.2.3. DNA extraction using Chelex

The Chelex method (Walsh et al., 1991) provides a very rapid way to isolate DNA from degradative enzymes and from some of the potential contaminants that might inhibit experiments.  In principle, the Chelex resin will trap such contaminants, leaving DNA in solution. In practice, Chelex extractions can be prone to degradation, and should be kept in the freezer when not in use, or these extractions should be used within 24 hours of extraction. If the extracted tissues contain pigments and other inhibitors for downstream experiments, it is often successful to dilute the Chelex extraction 1:9 with distilled water before use. Finally, when drawing from these extractions it is important to pipette from the top of the aqueous layer, avoiding the resin itself. Below is a recipe that works well for legs from adult bees or beetles, for whole varroa mites, or for other tissues of about that size.

  1. Add two posterior legs into Eppendorf tubes.
  2. Allow them to dry until the EtOH evaporates.
  3. Transfer to each tube:
    100 µl of Chelex® (5% solution in water),
    5 µl of proteinase K (10 mg/ml).
  4. Incubate the samples in a thermocycler with the following program:
    1 h at 55 °C,
    15 min at 99 °C,
    1 min at 37 °C,
    15 min at 99 °C,

    Pause at 15 °C.