Gel Electrophoresis

Bands

A DNA ladder usually contains a set of known DNA fragments with different sizes in base pairs (bp) or kilobases (kb). These DNA fragments are separated and visualized as DNA bands on a gel.

Gel electrophoresis

A technique used to separate segments of DNA based on their size using an electric current

Third step in gel electrophoresis

An electric charge is applied to the gel. The negatively charged DNA moves toward the positive side of the gel.

DNA ladder

These separated DNA bands together look like a ladder on the gel.

STR

(short tandem repeat) tandem repeats of short DNA sequences (2-5 base pairs) with varying numbers of repeats found among individuals

VNTR

(variable number of tandem repeats) tandem (next to each other) repeats of a short DNA sequence (9 to 80 base pairs) with varying numbers of repeats among individuals

Why do gel electrophoresis?

1. To determine which organisms are most closely related. 2. To determine paternity of a child. 3. For crime scene analysis.

Restriction Enzyme

Cuts DNA molecules at a specific base sequences (either STR or VNTR) to make smaller fragments

Results of gel electrophoresis

DNA fragments are separated by size. Smaller fragments move the furthest while larger fragments will be closer to the loading well. These are seen as bands within the gel.

First step in gel electrophoresis

DNA is first cut using special enzymes called restriction enzymes.

What is gel electrophoresis for?

It is used to separate DNA fragments based upon size.

Shorter DNA fragments

Move faster through the gel and end up further from the wells .

Longer DNA fragments

Move slower through the gel and end up closer to the wells.

Second step in gel electrophoresis

The DNA sample is loaded into an agarose gel.

Wells

The spaces that are loaded with DNA samples

DNA fingerprint

Unique sequence of DNA base pairs that can be used to identify a person at the molecular level

DNA probe

a molecule labeled with a radioactive isotope, dye, or enzyme that is used to locate a particular sequence or gene on a DNA molecule