Gel Electrophoresis draws an agarose gel with up to 12 lanes: a DNA ladder (a 100 bp ladder, a 1 kb ladder or λ DNA cut with HindIII) and sample lanes holding the band sizes you type. Each band runs as far as its size takes it on the gel you pick, so smaller fragments run farther, sizes too big or too small for the gel crowd toward its ends, and bands too close to separate run together as one thicker band. Start from a crime scene, paternity test, restriction digest or PCR experiment, then change anything.
Teachers use it for DNA fingerprinting, forensics and paternity questions, restriction mapping, PCR results and sizing fragments against a ladder. Leave a sample lane empty for students to draw its bands, swap the ladder’s sizes or the electrodes’ signs for blanks, or add a ruler for a standard curve. The answer key prints the sample lanes’ band sizes under the figure.
Copy the figure straight into a test, worksheet or slide, or download it as a PNG or SVG. Printing the page prints just the figure. Share link copies the page’s address with your settings in it, so anyone who opens it sees this exact figure, and presets save settings you use often in your browser. It’s free, with no sign-up.
DNA is negatively charged, so in the electric field it moves away from the negative electrode (cathode) at the wells toward the positive electrode (anode). The agarose is a mesh of tiny pores, and shorter fragments slip through it more easily than longer ones, so in the same time they travel farther from the wells.
A ladder is a mix of DNA fragments of known sizes run in its own lane. Compare a sample band with the ladder bands beside it: a band level with the 3000 bp ladder band is about 3000 bp, and one between the 2000 and 1500 bp bands is between those sizes. For a closer estimate, measure how far each ladder band ran, plot size on a log scale against distance to make a standard curve, and read the unknown band’s size from its distance.
The suspect whose lane has every band the crime scene sample has, at the same heights and no others, matches. A suspect with even one band that is missing or in a different place is not a match. In a paternity test, every band in the child’s lane must come from the mother or the father, so the true father has every band the child has that the mother doesn’t.
Pick the gel by the sizes you want to separate. A low-percentage gel has bigger pores and separates large fragments, while a higher one separates small fragments. Here a 0.8% gel separates about 800 to 10,000 bp, a 1% gel about 500 to 10,000 bp, a 1.5% gel about 200 to 3000 bp, and a 2% gel about 100 to 2000 bp, so PCR products of a few hundred bp suit a 2% gel with a 100 bp ladder.
A band with more DNA in it stains darker, or glows brighter. Ladder bands are drawn with the amounts of DNA their makers list, so reference bands like the 1 kb ladder’s 3000 bp band stand out. Type “x2” after a sample’s size for a darker band and “x0.5” for a fainter one. Two sizes too close for the gel to separate are drawn as one thicker band, and the settings say which sizes ran together.
Yes. Clear a sample lane’s band sizes to leave it empty on the figure, for example the double digest after the two single digests. Set Ladder sizes or Lane labels to Blank lines, or Electrodes to Blank, for students to fill those in too.
Yes. A ladder can go in any lane, and a gel can have more than one. Its sizes are written beside it only when it is the first or last lane, so put a ladder at an end if students need its sizes labeled.
Biology Figures Gel Electrophoresis