DNA Technology and
Genomics
Chapter 20
A. P. Biology
Mr. Knowles
Liberty Senior High School
Restriction Endonucleases
• Enzymes that recognize specific DNA
sequences in dsDNA (usually 4-6 bp
sequence of nucleotides) and digest the
DNA at this site.
• Produce fragments of DNA of various
lengths. Restriction Fragments.
• Restriction Enzymes isolated from many
species of bacteria.
Restriction Enzymes
• Several hundred isolated.
• Specifically named:
Ex: EcoRI
E = genus
co = species coli
R = strain RY13
I = first endonuclease isolated
Some enzymes...
• Others cleave each strand off-center
at specific nucleotides to produce
“overhangs”-sticky end cutters. Ex.
EcoRI
• Cut cleanly through the DNA at the
same position on both strands- blunt
end cutters. Ex. Hae III
How Do You Separate
DNA Fragments?
• Electrophoresis- the separation
of DNA fragments based upon
the negative charge of the DNA
and its size.
• DNA is negatively charged
because of phosphates.
DNA Fingerprinting or ProfilingMany Applications
Genetic Variation
• Any two humans have nearly identical
sequences of DNA (99.9%).
• But 0.1% is = to 3.0 X 106 nucleotides
(recall the genome is 3.0 X 109
nucletotides).
• DNA profiling takes advantage of
polymorphisms (many forms) of repeated
sequences in noncoding regions of DNA
(near centromeres or ends of chromosomes)
Two Kinds of Polymorphisms
• Variable Number Tandem Repeats (VNTR’s)
– 9-80 nucleotides that repeat next to each other;
the number of times they repeat varies.
• Short Tandem Repeats (STR’s) – 2-8
nucleotides that repeat; also variable in the
number of repeats.
• VNTR and STR patterns are inherited from each
parent; one set from each parent. Can be used in
paternity testing, crimes scene identification,
conservation biology, etc.
What’s the point?
• Use different restriction enzymes to
make a restriction map- relative
positions of sites cut by the enzymes.
• Allows you to recombine DNAs of
different organisms-recombinant
DNA technology.
• Allows you to identify and match
DNAs; DNA Fingerprinting.
Restriction Enzymes Identify
Genetic Disease
• Mutations in a gene change the length
of the DNA fragments cut by restriction
enzymes.
• These different lengths are called
Restriction Fragment Length
Polymorphisms (RFLPs).
• Fragments can be separated by
electrophoresis.
An Application
• Glow-in-the-Dark Pets?
• http://www.msnbc.msn.com/id/30463427/