Luckau Protocols:1Kb Ladder

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1Kb Ladder Mix

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Nucleic acid ladder is used as a size standard in agarose gel electrophoresis. It contains DNA molecules of known lengths. The ladder is pre-mixed with gel load buffer (color dyes with varying mobility on an agarose gel) for direct transfer to the gel.


Invitrogen 1Kb Plus DNA Ladder

(We used to use Invitrogen's 1Kb DNA Ladder, catalog# 15615-016, Media:Invitrogen_1KbLadderProductManual.pdf, Media:1kb Gel Ladder Map.jpg, but they have since discontinued this product. The two products are compatible.)

Promega Blue/Orange Loading Dye, 6x

  • catalog# G1881
  • use at 1x concentration
  • contains:
0.4% orange G
0.03% bromophenol blue
0.03% xylene cyanol FF
15% Ficoll® 400 (for density; replaces glycerol)
10mM Tris-HCl (pH 7.5)
50mM EDTA (pH 8.0)
  • In a 0.5–1.4% agarose gel in 0.5X TBE:
xylene cyanol FF migrates at approximately 4kb
bromophenol blue at approximately 300bp
orange G at approximately 50bp.

Other Knowns

  • well width (21-tooth comb) = 7mm
calculations made for 6mm width, since they end up being more convenient



  • 6mm x (0.1µg ladder)/(1mm width) x (1µL/1µg) = 0.6µL ladder per well
  • 6 \mbox{ mm} \bullet \tfrac{0.1 \mbox{ } \mu \mbox{g ladder}}{1 \mbox{ mm width}}\ \bullet \tfrac{1 \mbox{ } \mu \mbox{L}}{1 \mbox{ } \mu \mbox{g}}\ = 0.6 \mbox{ } \mu \mbox{L ladder per well}
  • Per well: 0.6 µL ladder + 4.4 µL H2O + 1 µL loading dye = 6 µL ladder mix

Make Ladder Mix

120 µL ladder + 880 µL H2O + 200 µL loading dye = 1200 µL ladder mix

Ladder Map

Migration of Gel Load Dyes (using old ladder)

  • Bromophenol Blue (175bp) and Xylene Cyanol FF (1500bp)
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