Welcome to Earl's Forensic Page

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DNA is the building block of the body. It is present in every nucleated cell.
DNA extracted from the cells may be used to form a forensic profile.



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This is an actual RFLP of a forensic profile from a homicide case. The victim's profile is lane 18, the suspect is in lane 3 and all of the other drops of blood tested matched the suspect in lane 3. To verify the gel worked properly a known control is in lane 2. Lanes with many bands are ladders used to measure the sample bands. The probe used was D2S44. It is one of a series used to characterize a sample.

RFLP is used when we have a lot of sample,e.g. blood stains the size of a quarter. We do not always have that much sample. PCR methods may be used on very small samples,e.g. a speck of blood, tissue under a fingernail, saliva from a cigarette butt or postage stamp. There are two common methods of PCR detection, Dot blot which produces colored dots and STR's which use electrophoresis to separate the alleles.

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Very small samples are amplified using PCR. This is a DQa result by PCR. You read any blue dot darker than the C dot. The above strip shows a 1.3,4 type.
 [IMAGE] Each of the DNA methods display two alleles. These are a direct result of having two parents. One allele is inherited from each parent. It is this reason that DNA may be used to determine paternity.

This is a graphical representation of an rflp paternity profile. One can conclude that the alleged father is included in the group of possible fathers, based on the one shared band between the alleged father and the child. The liklihood of the alleged father being the actual father will increase if other primers are used and continue to show at least one common band between the alleged father and the child.

Match of two cases committed by the same person a year apart. Six unrelated loci were tested.

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Most Forensic labs are switching to STR's (Short Tandem Repeats) as their method of DNA analysis. Below is the result of an STR run by CE (Capillary Electrophoresis).

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STR typing using capillary electrophoresis and AmpFISTR COfiler (TM Perkin Elmer) This sample shows six loci and the gender determining amelogenin. The ladders at the bottom show all of the possible alleles.
Capillary electrophoresis separates DNA inside a tube the diameter of a hair.

Want to learn more about CE? see ABI310

How stable is DNA?

Many times people argue in court that samples were handled badly, degraded or put in plastic..The simple fact is..if you have a teacup and saucer and smash it with a hammer, it will not come back as a dinner plate! (messler) Likewise, DNA that is degraded turns into a pile of smaller bits of DNA.
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What's happening in Forensic DNA? Read Promega's Profiles in DNA

Not Bored yet? Try these.....Lifecodes
Perkin Elmer
Thanks to Tom Zinnen and Lana Hays for their assistance.

To learn more about Forensic DNA see an interview with DNA Forensic Authority, Dr. Bruce Weir.

To learn more about forensic science check out Forensic Science.
To find out about other forensic topics, education or thread to Dr. Henry Lee check out Reddy's Forensic Page.

High school teachers wanting resources in Biology may check out Access Excellence and Cold Spring Harbor Laboratory's DNA Learning Center.

For a list of Forensic Supply vendors click here.


Interface '99 "WhoDunnit?" attendees with special requests may contact me here.

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 visitors since May 22, 1997