Ellie Landis

What is Gel Electrophoresis?

Gel electrophoresis is a process that separates

fragments of DNA based on their sizes.

Step 1Place DNA into tubes

DNA can come from tissue or

body fluid, such as cheek cells, blood, skin, and

hair.

Step 2Polymerase Chain Reaction

The polymerase chain reaction uses a

machine called a thermocycler to quickly

copy a piece of DNA.

Continue these three steps 30 to 40 times to

get lots of copies of DNA.

Step 3Place restriction enzymes into DNA

The restriction enzymes cut the DNA

into different sizes according to it’s

sequence.

Step 4Dye DNA and place into gel

The gel is made out of agarose, which is similar to jello.

The gel is made with wells at one end so that the

DNA can be loaded into the gel.

Step 5Run electric current through gel

DNA is negatively charged so it will move towards the positively charged

end of the gel.

Step 6Smaller pieces of DNA travel farther than

Larger pieces of DNA

End result!

Gel Electrophoresis is used to...

Solve criminal casesSolve paternity casesDiagnose genetic diseasesDetermine genetic kinship among species

Pros ConsEasy to doDNA does not get ruined in

the processYou only need a small

amount of DNA to start with

DNA can be detected no matter what size it is

ExpensiveTime consumingUses hazardous material

Tommie Lee Andrews CaseTommie Lee Andrews was the first person in

the U.S to be convicted with the help of DNA fingerprinting evidence. Andrews was convicted for strangling two teenage girls. The judge in Andrews’ first trial did not allow the DNA fingerprinting evidence, although Andrews ended up having a second trial. The judge in his second trial did allow the DNA fingerprinting, which proved Andrews guilty and he was convicted in 1987. This is just one of many cases that DNA fingerprinting/gel electrophoresis has been used to solve a crime.