Gel electrophoresis separates fragments of DNA (or proteins) according to their size. It is used to compare the DNA of different organisms.
1. DNA is cut into fragments using restriction enzymes, which cut at specific base sequences.
2. The fragments are loaded into wells at one end of an agarose gel, which sits in a tank of buffer solution. The wells are at the negative electrode (cathode) end.
3. A voltage is applied across the gel. DNA is negatively charged because of its phosphate groups, so the fragments move through the gel towards the positive electrode (anode).
4. The gel acts like a sieve. Smaller fragments move more easily through the pores, so in a given time they travel further from the wells than larger fragments.
5. The DNA is stained with a dye (or labelled with a fluorescent or radioactive marker) so the fragments show up as bands.A DNA ladder, a mixture of fragments of known sizes, is run in one lane so the sizes of the other fragments can be estimated.Comparing species: DNA from different species cut with the same restriction enzymes gives a pattern of bands. The more bands two species have in common, the more similar their DNA and the more closely related they are.Worked example: species A shares 6 of its 8 bands with species C, while species B shares only 2 of 8 bands with C. Species A is more closely related to species C.
1. DNA is cut into fragments using restriction enzymes, which cut at specific base sequences.
2. The fragments are loaded into wells at one end of an agarose gel, which sits in a tank of buffer solution. The wells are at the negative electrode (cathode) end.
3. A voltage is applied across the gel. DNA is negatively charged because of its phosphate groups, so the fragments move through the gel towards the positive electrode (anode).
4. The gel acts like a sieve. Smaller fragments move more easily through the pores, so in a given time they travel further from the wells than larger fragments.
5. The DNA is stained with a dye (or labelled with a fluorescent or radioactive marker) so the fragments show up as bands.A DNA ladder, a mixture of fragments of known sizes, is run in one lane so the sizes of the other fragments can be estimated.Comparing species: DNA from different species cut with the same restriction enzymes gives a pattern of bands. The more bands two species have in common, the more similar their DNA and the more closely related they are.Worked example: species A shares 6 of its 8 bands with species C, while species B shares only 2 of 8 bands with C. Species A is more closely related to species C.