Review:
• We extracted DNA from wheat germ
• And discovered that the color of DNA is …
WHITE!
• No matter what organism it comes from,
DNA in a tube looks the same!
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So how can scientists tell different DNA apart?
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So how can scientists tell different DNA apart?
• Remember that DNA is a long molecule of
A, T, G, C
ATTTCGCAAT
TAGGCATCGGACGTAGCC
TAGGCAGTCGATCGTCAGTCTTC
TAACCGGATACCAGACCAGGTCCCG
TTAACGCGGATATAGCCTGTCAGCTGAT
GGACATCGACTCTGAACTCGACACATCCCT
TAACCGATCGTCTCTGACCTCGACCTGACG
CGGTAACTGATCTCCCGATCCCCGATCCTGA
TGACACAGCTCGACTCCGACATCGCCCAGC
TTAAGCTACGGGACTAGCATCGATCGATCG
TTGACCAGCTAGCTCTGACCTCGACCTGAC
CGGGATAGCTCTAGCTCTGAGAGCTCG
TGAAACCGTAAAATCGTCTCTGATATAG
CCCGACCTTCGGATATACGTTCTG
TTAGACTGTGACAGCTTAGC
TAGCGGTAGATCGA
TAGCT
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+
Restriction
Enzymes
which act like
Chemical
“scissors”
So how can scientists tell different DNA apart?
• Remember that DNA is a long molecule of
A, T, G, C



CAT
CAT
ATGGTACGCATGGTCTCGAGCATAGCTTTCATGGCTT
CAT
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Result:
• Lots of different size pieces of DNA
CTCGACCTCAT
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Next step is to sort the pieces by size
using Gel Electrophoresis
CTCGACCTCAT
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Gel Electrophoresis
• Gel is made from Agarose powder which
comes from seaweed
DNA pieces go here
Bigger pieces
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Smaller pieces
Apply electricity
DNA pieces separated by SIZE!
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So how do scientists tell different DNA apart?
• Everyone’s DNA is unique!
– So everyone’s DNA gets cut up differently!
Different DNA samples
Bigger pieces
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Smaller pieces
Apply electricity
Different Patterns!
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DNA Fingerprinting
• Unique DNA = Unique patterns
– Just like your fingerprints are unique!
Different DNA samples
Bigger pieces
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Smaller pieces
Apply electricity
Different Patterns!
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DNA Fingerprinting
• Unique DNA = Forensic
Unique
patterns
Scientists
use it to solveare unique!
– Just like your fingerprints
crime scenes
Different DNA samples
Bigger pieces
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Smaller pieces
Apply electricity
Marine Biologists
use it to identify
new species
Different Patterns!
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• In labs we use a carcinogen called EtBr to
make the DNA show up
• Food color dyes have their own color!
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Who should understand DNA?
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