DNA Fingerprinting

3.3.1 Interpret how DNA is used for comparison and identification of organisms.

Gel Electrophoresis A technique used to separate molecules based on size. Look at the name to remember the requirements: gel and electricity.

DNA Fingerprint The result of gel electrophoresis is a DNA fingerprint. We call it a fingerprint because your DNA identifies you, just like your fingerprints. Gel is stained using ethidium bromide which binds to DNA it shows up as bands in UV light Draw attention to the fact that small mols are at the bottom of the gel and large ones stay nearest to the wells

Why electricity works? DNA has a negative charge, so the fragments will travel towards a positive electrode.

Steps Involved in Gel Electrophoresis 1. Make the gel. 2. Use restriction enzymes to cut DNA into different sized fragments. 3. Load the DNA fragments into the gel. 4. Apply the electric current to the chamber and wait. Restriction enzymes cut at various sequences. If this DNA fragment is cut with EcoRI it will cut the sequence when ever it reads GAATTC.

Arrangement of DNA Fragments Shorter fragments can weave through the gel easier than larger fragments so they are found towards the bottom.

Applications of DNA Fingerprinting Crime scene investigations Paternity testing Identifying/cataloging species (including extinct) to determine relationships or similarities

Crime Scene Investigation Examples In crime scene investigations, crime scene DNA must match exactly with a suspect. Answer: Suspect 2

Paternity Testing Examples In paternity testing, each fragment of a child’s DNA must match with one of its parents. Answer: Dad 2

Comparing Various Species DNA Example In species cataloging, the more DNA a species has in common with another species means they are more closely related. Answer: The sample DNA is most similar to Species 1, because they share 3 out of 4 DNA fragments in common.