Dna fingerprinting
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DNA Fingerprinting. Use of DNA to Determine Identity. DNA controls production of proteins Results in phenotype (eye color, facial features) Contributes to structure and function DNA – 3 billion base pairs No other person on planet has same code (except identical twins!)

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DNA Fingerprinting

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Dna fingerprinting

DNA Fingerprinting


Use of dna to determine identity

Use of DNA to Determine Identity

  • DNA controls production of proteins

    • Results in phenotype (eye color, facial features)

    • Contributes to structure and function

  • DNA – 3 billion base pairs

    • No other person on planet has same code (except identical twins!)

  • Only 0.1% of DNA differs from person to person

    • But the regions that do vary provide a true genetic blueprint


Use of dna to determine identity1

Use of DNA to Determine Identity

  • DNA obtained from skeletal remains

  • DNA purified

  • If degraded – amplified w/ PCR

  • RFLPs compared to determine final identity of missing person


What are some sources of dna evidence

What are some sources of DNA Evidence?

  • Skin cells

  • Hair

  • Blood

  • Semen

  • Anything with DNA


Dna fingerprinting1

DNA Fingerprinting

  • AKA - DNA profiling analysis or DNA typing

  • Electrophoretic analysis of DNA fragment sizes generated by restriction enzymes

  • Provides accurate, unambiguous identification of source DNA samples


Restriction enzymes

Restriction Enzymes

  • Endonucleases that cut phosphate bonds

    • Break bonds between deoxyribose and phosphate

  • Attach to DNA and “read” nucleotides

  • Cut at specific sequences

  • Over 3000 types


Restriction enzymes1

Restriction Enzymes

  • Named after the organisms from which they were discovered / isolated

  • Eco RI – Escherichia coli RY13

  • Hind III – Haemophilus influenzae R4

  • Bam HI – Bacillus amyloliquefaciens H


Eco ri function

Eco RI Function

Eco RI

5` - G A A T T C – 3`

3` - C T T A A G – 5`

5`- GA A T T C – 3`

3` - C T T A A G – 5`

DNA fragments with “sticky” ends


Restriction enzymes2

Restriction Enzymes

  • Forensic labs – use at least 2 restriction enzymes

    • 4-base and 5-base (sometimes others)

  • Size of DNA fragments – depends on distance between recognition sites

  • Longer DNA molecule – the greater probability that a specific recognition site will occur


Restriction enzymes3

Restriction Enzymes

  • Average human chromosome = 100 million bp

  • Eco RI – 6 bp recognition site

  • Probability – 1 site / 4096 bp

  • Cut human DNA into ~25,000 fragments


Restriction enzymes4

Restriction Enzymes

  • No two individuals have same pattern of restriction enzyme recognition sites

  • Each person – unique genotype (different alleles)

  • Mutations / Insertions / Deletions

    • Changes distribution and frequency of restriction enzyme recognition sites


After restriction digest

After Restriction Digest

  • Analyze DNA fragments on agarose gel

  • DNA fragments separated by molecular weight (size) due to net negative charge on phosphates

  • Restriction enzyme cleavage of relatively small DNA molecules – key to RFLP analysis

  • If DNA fragments are too large – can’t see RFLP pattern


Sample rflp patterns

Sample RFLP Patterns

Suspect RFLP #4

Control RFLP

Suspect RFLP #1

Suspect RFLP #3

Suspect RFLP #5

Suspect RFLP #6

Molecular Marker

Suspect RFLP #2


Restriction enzyme digestion

Restriction Enzyme Digestion

  • Be sure to label all reaction tubes (4)

    • 10 μl of enzyme reaction buffer

    • 15 μl of DNA sample from missing person

    • 15 μl of Restriction Enzyme

  • Incubate at 37°C for ~60 minutes

  • Add 5 μl of Gel Loading Solution after incubation


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