DNA Facts
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Watson & Crick 1953
Contains all Genetic info
½ from each parent
¾ like siblings
Double helix
Unique?????
In all cells with nuclei
Made of nucleotides with nitrogen
bases ATCG
98.5% is Junk… non-coding DNA,
that’s what makes you unique
Also found in mitochondria…from
mom
Sources of DNA
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Blood
Saliva
Semen
Vaginal fluid
Skin cells
Hair with follicle
Obtaining DNA from a suspect
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A warrant is needed
Garbage can be used…….
Tissue, coffee cup, straw
Certain convicted felons in NYS must submit DNA sample
Since January 1, 1996, the law in New York State has required
offenders convicted of certain felonies to submit biological
samples (formerly blood and more recently buccal samples
swabbed from the inside of the cheek) for DNA profiling through
laboratory analysis.
The resulting records of offender DNA profiles are organized into
a centralized index within the State DNA Data Bank—a part of
CODIS, the national Combined DNA Index System developed by
the FBI.
CODIS…
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Combined DNA INDEX System
DNA database funded by the United States Federal
Bureau of Investigation (FBI).
It is a computer system that stores DNA profiles
created by federal, state, and local crime
laboratories in the United States, with the ability to
search the database to assist in the identification of
suspects in crimes.
Congress formally authorized the FBI to operate
CODIS and set national standards for forensic DNA
testing. Although the Act was passed in 1994,
CODIS did not become fully operational until 1998.
Creating a DNA Profile
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Extraction
Use of Restriction Enzymes
Amplification
Electrophoresis
Extraction
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DNA is extracted from the cells
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Strong detergents are used to remove the DNA from
the membranes that hold it.
You can do DNA extraction at
home…
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All the materials and equipments to carry out the experiment are items commonly found in the
household.
Pour 3/8 cup of water into a cup.
Add 1/4 teaspoon of salt and clear liquid soap into the cup, and stir for the salt to dissolve. The
soap causes the cell walls to break up, freeing the DNA inside. The salt is for keeping the DNA
molecules together.
Place the organic materials into the sandwich bag or blender and mash or crush until completely
pulverized. This is to break the cells apart.
Add 2 teaspoons of the soap-salt solution to the bag. Mix gently by compressing or rocking the
bag for at least 1 minute.
Pour the mixture through coffee filter into a clear jar. Let it drain into the jar for 10 minutes.
DNA extraction at home
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Meanwhile, pour 1/4 coup of rubbing
alcohol into another clear jar and put
the jar in the freezer or a bowl of ice.
The alcohol helps strip the water
molecules from the outside of the
DNA molecules, causing the
molecule to collapse on itself and
separate from the proteins in the
solution.
After 10 minutes have elapsed, pour
the strained liquid into the alcohol.
Let the jar sit still for at least 5
minutes. The final product contains
a layer of proteins and a cloudy
layer of DNA clumped together. The
naked eyes cannot resolve the
individual macromolecules within.
Use of Restriction Enzymes
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Used to cut the DNA into shorter fragments
The enzymes cut the DNA at a specific
sequence of bases (recognition site)
These fragments are called VNTRs (variable
number tandem repeats) and STRs (short
tandem repeats)
Use of Restriction Enzymes
VNTRs
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short sequences of DNA that contain 9-80
bases with a repeated sequence
ex. CATACAGAC CATACAGAC
CATACAGAC
In one person it might repeat 3x in another 7x
STRs
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More useful in DNA analysis
Shorter than VNTRs
2-5 bases repeated
Ex. GATA GATA GATA GATA GATA
More accurately used, easier to separate
Degraded DNA can also be analyzed
Amplification
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PCR (polymerase chain reaction) used to
amplify the amount or DNA Generates
multiple identical copies of small amounts of
DNA
Billions of copies of the DNA sample can be
made in a few hours
Invented in 1993 by Dr. Gary Mullis
Used in Jurassic Park
PCR
Electrophoresis
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Separates the DNA fragments by size and
polarity in an electric field
The DNA moves through the field by size,
smaller fragments move more quickly through
the gel
The fragments form band with the shortest
fragments closest to the (+) end
Gel Electrophoresis Apparatus
Electrophoresis
The RESULTS……..
Uses of a DNA profile
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Match Crime scene DNA to suspect’s DNA
Eliminate suspects
Paternity/maternity tests
ID family members
ID human remains
Free those falsely accused