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DNA Analysis
Chapter 11
Learning Objectives
• Know the structure and function of
DNA.
• Understand how DNA is applied in
forensic science.
• Extract DNA from cells.
• Apply the concepts of RFLP, PCR,
and STRs to characterizing DNA.
• Comparing DNA fingerprints.
Biology of DNA
• Cell – the smallest unit of life.
Biology of DNA
• Nucleus – the control center of the
cell.
Biology of DNA
• Chromosomes – long, threadlike
groups of genes found in the nucleus.
Biology of DNA
• DNA (deoxyribonucleic acid) –
hereditary material of most
organisms.
Biology of DNA
• Gene – a specific sequence of
nucleotides in the DNA that codes to
make specific proteins.
Function of DNA
• Sections of DNA, called genes, code
for specific proteins.
• Proteins then determine human traits.
Structure of DNA
• DNA – a long-chain molecule made of
four bases that are paired and held
together with hydrogen bonds and a
sugar-phosphate backbone.
Nitrogen Bases
•
•
•
•
Adenine
Thymine
Guanine
Cytosine
Complimentary Base Pairs
• Adenine and thymine are connected
with two hydrogen bonds.
• Cytosine and guanine are connected
with three hydrogen bonds.
Backbone of DNA
• Deoxyribose –
sugar in DNA
• Phosphate
groups
Nucleotides
• Nucleotide units = base + sugar +
phosphate
• Outside – sugar and phosphate
• Inside – base pair & hydrogen bonds
Forensic Uses of DNA
• Identify a potential suspect whose
DNA may match crime scene
evidence
• Clear the wrongly accused
• Identify victims
• Establish paternity
• Match organ donors with recipients
Samples from Crime Scenes
• Determine if useful
• Specimen removed from object
(clothing, skin, weapon)
• DNA is extracted from cellular
components
• Enzymes release DNA from
chromosomes.
• DNA is ready for characterization.
RFLP Analysis
• Restriction Fragment Length
Polymorphism
• Restriction enzymes – recognize a
specific sequence of bases and cut
the DNA molecule at a specific point
• Probe – a portion of DNA with a
known sequence of bases that is
used to find its complimentary strand.
Statistical Analysis in DNA
Fingerprinting
• What are the chances of two people
having the same size fragment?
• Remember, we are not looking at the
sequence…only size.
PCR and DNA Fingerprinting
• Polymerase Chain Reaction – lab
technique used to make multiple
copies of DNA for further testing.
• Separation
• Adding Primer
• Synthesis of New Chain
STR: Short Tandem Repeats
• STRs – specific sequences of DNA
fragments that are repeated at a
particular site on a chromosome.
• VNTR – variable number of tandem
repeats.
• Scientists scan 13 regions of VNTRs.
Example VNTR
Mitochondrial DNA
• Mitochondria – power houses of the
cell.
• Mitochondrial DNA comes from the
mother.
• Analysis takes much longer and is
much more expensive.