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DNA - PowerPoint PPT Presentation

  • Uploaded on Ch. 9. DNA. Enduring Understanding:. Forensic Science involves many different scientific technologies. Essential Question:. How is DNA used in Forensic Science?. What do you know about DNA????.

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Ch. 9


Enduring Understanding:

Forensic Science involves many different scientific technologies

Essential Question:

How is DNA used in Forensic Science?

What do you know about DNA????

History of DNA

James Watson and Francis Crick


Maurice Wilkins

Rosalind Franklin



DNA structure


sugar - deoxyribose

phosphate group

nitrogen base

cytosine - guanine

adenine - thymine

Complementary Base Pairing

Adenine - Thymine

Cytosine - Guanine

Ave. human chromosome = 100 million base pairs

Function of DNA:

-defined by the arrangement of base pairs

- protein synthesis

-20 amino acids

- normal hemoglobin vs. sickle cell

hemoglobin Cell

valine valine

histidine histidine

leucine leucine

threonine threonine

proline proline

glutamate valine

glutamate glutamate

. .

. .

. .

DNA replication

-synthesis of DNA from existing DNA

-DNA polymerase

-assemble new strand of DNA

-proofread DNA for mismatched base pairings

Polymerase Chain Reaction

use in forensic science:

-DNA thermal cycler

- small amount of DNA

- millions of copies

***sample size does not limit amount of tests run

Recombinant DNA

process used to insert DNA from one organism into the DNA of another organism

mice with green fluorescent protein from jelly fish

How does recombinant DNA technology work?

1. use a restriction enzyme to cut DNA into fragments (150 different restriction enz.)

2. insert the isolated DNA strand into a foreign DNA strand, usually bacteria

-restriction enz used to open up foreign DNA

3. new DNA is spliced into foreign DNA, then put back into bacteria

DNA Typing with Tandem Repeats

human genome has repeating sequences of bases

(30%) = tandem repeats

Restriction Fragment Length Polymorphisms


-15-35 base pairs long, repeats up to 1000 times

-*numerous possibilities for the # of times a particular sequence of base letters can repeat itself on a DNA strand

can be used to tell different people apart

used to link Monica Lewinsky's dress with President Clinton

Gel Electrophoresis

-technique that separates materials according to migration through a gel under an electrical field

-use starch or agar gel

-What types of substances would move?

- match up bands

Mitochondrial DNA

DNA found in mitochondria - in loop form

can be used if hard to find nuclear DNA - charred body or hair shaft

can get from maternal related relative if can't get from body

- costly, harder to perform, time consuming

first mtDNA evidence in 1996 of Tennessee vs. Paul Ware

linked 2 hairs to suspect

used to identify remains put in Tomb of Unknown Soldier as First LT. Micheal J Blassie (1998)

-took remains of mtDNA and compared to 7 families associated with case

-identified the remains to be Lt. Blassie