Name__________________________Date_______________

DNA FingerprintingA Killer Lab

What is DNA fingerprinting?A technique used by scientists to distinguish between individuals of the same species using only samples of their DNA. DNA fingerprinting depends on regions of non-coding (does not contain the code to make a protein) DNA that show great variability between individuals.

1. Write a definition of DNA fingerprinting in your own words.

What steps are involved in making a DNA fingerprint?1. Cell membranes are broken to release DNA.2. Copies of the DNA are made using PCR.

a. PCR (polymerase chain reaction) involves heating and cooling cycles that produce millions of copies of selected parts of a DNA molecule. PCR is especially important in crime scenes when extremely small samples of DNA are collected.3. DNA is cut into fragments using restriction enzymes.

a. Restriction enzymes cut DNA at specific base sequences.4. DNA fragments are separated according to size using gel electrophoresis.

a. Shorter pieces of DNA travel farther from the spot they were loaded into the agarose gel because the smaller molecules, fit through the pores in the agarose gel

Forensic Scientists make DNA fingerprints from DNA found in various types of human cells (sperm, blood, hair, etc.). A restriction enzyme recognizes a certain area of a DNA molecule and then cuts the DNA at that location. Each restriction enzyme makes a cut at one particular sequence of bases. For example, the restriction enzyme EcoR1 cuts DNA at the following base sequence: C/AATTC.

After the DNA is cut, the fragments are poured into wells on a gel plate. The plate is hooked up to an electric current so that end where the DNA starts is negative and the other end is positive. Because DNA is negatively charged it moves toward the positive end of the gel. Fragments that are smaller move faster, while the larger fragments stay near the start of the gel. If the current is not turned off, all fragments will eventually run to the end of the gel and combine in one large blot.

After the gel is allowed to run for a designated time, probes are added so that we can see the DNA. The gel is then developed an a scientist can analyze the results. The unknown DNA can be compared to known suspects. Because an individual’s DNA is the same in all of his cells, it does not matter where the sample came from. The fragments will match completely if the DNA samples are from the same person.

When determining the parents of a child, you examine the child’s DNA fingerprint first. Each fragment of DNA the child possesses came from one of its parents. If a child has a DNA fragment 13 bases long, either the mother or the father, or both, had to pass this fragment on to their child. A child can not have a fragment of DNA that neither one of its parents have.

Name__________________________Date_______________

DNA fingerprinting can also be used to determine who was at a crime scene, the identity of unrecognizable remains, conservation biology and evolutionary studies.

Name__________________________Date_______________

Name__________________________Date_______________

Name__________________________Date_______________

Name__________________________Date_______________

Name__________________________Date_______________