West Coast Green Crab Experiment Part 46

PCR and gel for TTR crabs

Last time my PCR came back contaminated, so looks like we’re starting Round 3 of “why am I in contamination station?!” Vanessa took the lead on this PCR.


  1. IF STARTING HERE: Use RNAse AWAY to clean bench space, pipets, tip boxes, etc. Put pipets, tip boxes, and tube racks with open clean tubes into the UV Crosslinker.
  2. Label either an 8-strip PCR tube or a 96-well plate with sample ID and “P” (ex. 3P) and a 1.5 mL eppendorf tube “PCR MM.” Be sure to label an extra tube for the PCR blank.
  3. Calculate the amount of reagents needed for PCR master mix for samples, a PCR blank, and two extra reactions.
    • GoTaq: 12.5 µL/sample
    • SMC F primer: 2.5 µL/sample
    • SMC R primer: 2.5 µL/sample
    • DEPC H2O: 5.5 µL/sample
  4. Preheat the thermocycler with the TD65_48L PCR protocol
  5. Get ice and thaw PCR reagents and DNA at room temperature. Briefly vortex, spin down, and move onto ice as soon as reagents thaw.
  6. IF NEEDED, make new SMC F and R primer aliquots. Take the 100 µM stock bottles (blue lids) and dilute into a new, labelled 1.5 mL eppendorf tube in a 1:10 dilution (ex. 10 µL primer stock, 90 µL NF water).
  7. Make master mix based on calculations in step 3 in the labelled PCR MM tube. Vortex, spin down, and keep on ice.
  8. Aliquot 23 µL of PCR MM from step 6 in each tube for the samples, extraction blank, and PCR blank.
  9. Once the DNA thaws, briefly vortex DNA and spin down. Place on an ice block tube holder.
  10. Add 2 µL of DNA into each sample tube. Add 2 µL DEPC water for the PCR blank.
  11. Seal wells completely. Use tube/well caps, foil plate seal, or Microseal A film to seal plates. Use roller to push down seal and use the plate sealer tool to ensure all wells are completely sealed.
  12. Vortex the sealed tubes and briefly spin down.
  13. Place in the thermocycler, close lid, and run TD65_48L PCR protocol.
  14. When protocol is complete, place PCR product in the 4ºC fridge until ready to load a gel.


  1. Obtain PCR product, ladder, and TriTrak from the 4ºC fridge and move into gel room.
  2. Microwave pre-made gel mix in the microwave for 3 minutes in 1.5 minute intervals. Be sure to swirl the bottle to mix the gel liquid.
  3. Allow the bottle with gel mix to cool for a few minutes. While cooling, tape off sides of the gel tray.
  4. After bottle has cooled enough to the touch but the gel mix is still in liquid form, pour the mix into the taped gel tray slowly to avoid bubbles. Use combs to make wells by slowly inserting them into the gel to avoid bubbles.
  5. Allow gel to harden for at least two hours.
  6. Once gel is hardened, place in gel box with 1x TAE buffer. If an extra gel was made, slide and place in a Ziploc bag with TAE buffer. Place that Ziploc bag in the same drawer as the pre-made gel mix, away from the light.
  7. Obtain a piece of parafilm and pipet 1 µL of TriTrak dye for each sample, extraction blank, and PCR blank. On the parafilm, the dye will bead up. Place the dots far enough apart to avoid contamination.
  8. Take 6 µL of PCR product and mix with a 1 µL dot of TriTrak dye by pipetting up and down at least 10 times. Then, pipet up 6 µL and load gel. Repeat for each sample until halfway through samples. Then, add 2.5 µL of diluted ladder + dye mix, and continue with remaining samples.
  9. Run gel for 30 minutes.
  10. After running gel, remove gel tray and image.


  • Sent everything through the UV Crosslinker
  • Samples: 134, 161, 164, 181, 66, 144, 123, 154, 168
  • PCR Master Mix calculations
    • 12 samples + 1 PCR blank + 1 extra = 14 aliquots
    • GoTaq: 12.5 µL x 14 = 175 µL
    • SMC F: 2.5 µL x 14 = 35 µL
    • SMC R: 2.5 µL x 14 = 35 µL
    • NF H2: 5.5 µL x 14 = 77 µL


Screenshot 2024-04-10 at 10 57 49 AM

Figure 1. Gel image for 134, 161, 164, 181, 66, 144, ladder, 123, 154, 168, extraction blank, and PCR blank

Still contaminated!! But, the bands are not as bright as last time. I’m going to take apart pipets and clean again and see if that helps. I’m also going to take a subset of samples and run PCR with the C. maenas COI primers and the SMC primers to see if it’s a crab DNA contamination issue or of there’s something funky with the SMC primers or my most recent extraction batch.

Going forward

  1. Work with Vanessa to leave contamination station
  2. Re-extract and PCR samples with faint gel bands
  3. Work with Vanessa to continue with Chelex extractions, PCRs, and gels for remaining crabs
  4. Genotype remaining samples
  5. Examine HOBO data from 2023 experiment
  6. Determine best statistical approach for analyzing performance data
  7. Demographic data analysis for 2023 paper
  8. Update methods and results of 2023 paper
Written on April 5, 2024