Transcript Ch 14 Human Heredity

1 Review How do molecular biologists identify genes
in sequences of DNA
Use Analogies How is shotgun sequencing similar to
doing a jigsaw puzzle
2 Scientist one day may be able to use genomics to
alter a child’s inherited traits. Under what
circumstances, if any, should this be used and when
should it not be used? Write a persuasive
paragraph expressing your opinion by using specific
examples of traits.
CH 14 HUMAN HEREDITY
14.3 Studying the Human Genome
Cutting DNA

Restriction enzymes
 Cut
DNA molecules into pieces, called restriction
fragments, at precise locations

EcoRI restriction enzyme
 Recognizes
the sequence GAATTC
 Cuts each strand
between the G and A

“Sticky Ends”
 The
single strand overlap.
Separating DNA

Gel electrophoresis
 Separate
and analyze the differently sized DNA
fragments.
Gel Electrophoresis



Mixture of DNA fragments is placed at one end of a
porous gel
Electric voltage is applied and DNA molecules move
toward the positive end
Smaller DNA fragment move farther and faster.



Resulting pattern based on fragment size
Add stains to see DNA
Can remove individual fragments for further study.
Reading DNA



Single-stranded DNA is placed in a test tube
containing DNA polymerase and the four
nucleotide bases
DNA polymerase uses the unknown strand as a
template
Add a small number of bases that have a chemical
dye attached one for each base
 Dye
makes synthesis stop.



Result is a series of color-coded DNA fragments of
different lengths
Run gel electrophoresis
Order of colored bands on the gel tells the exact
sequence of bases.
The Human Genome Project

Main goal of sequencing all 3 billion base pairs of
human DNA and identifying all human genes.
Sequencing and Identifying Genes

Researchers mark the DNA
strands .
 Find
the base sequence in
different locations

“Shotgun sequencing”
 Cut
DNA into random
fragments, then determining
the base sequence in each.


Computer programs take
the sequencing data and
overlaps fragments
Align fragments relative
to the known markers.
Research Explores the Data from the
Human Genome Project



Look for a promoter
Shortly after is the reading
frame (become mRNA)
Find start and stop codons,
and introns and exons.
Comparing Sequences

People have very similar DNA
1

base in 1200 are different
SNPs (snips)
 Place

where there is a single base difference
Haplotypes
 Closely
linked SNPs that occur together
 May help identify diseases and conditions.
Sharing Data

Bioinformatics
 Combines

molecular biology with information science
Genomics
 Study
of whole genomes,
including genes and
their functions.
What We Have Learned
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
Working copy of the human genome June 2000
Full reference sequence April 2003
3 billion nucleotide bases
Only about 2 percent of our genome encodes
instructions.
What We Have Learned
What We Have Learned



Pinpointed genes and associated particular
sequences in those genes with numerous diseases
and disorders
Identified about three million locations where
single-base DNA differences occur in humans
Transferred important new technologies to the
private sector, including agriculture and medicine.
New Questions



Who owns and controls genetic information?
Is genetic privacy different from medical privacy?
Who should have access to personal genetic
information, and how will it be used?

President George W. Bush signed into law the
Genetic Information Nondiscrimination Act, which
prohibits U.S. insurance companies and employers
from discriminating on the basis of information
derived from genetic tests.
Modeling Restriction Enzymes
1.
2.
Write a random 50 base double strand DNA
sequence using the 4 DNA bases. Include each
sequence shown at least once
Make three copies of you double strand
sequence on three different colored strips of
paper
3. Use the drawings to see how the restriction
enzyme EcoRI would cut your sequence. Cut
apart one copy of your sequence
4. Repeat step 3 using the restriction enzyme
BamI on the second copy and the restriction
enzyme HaeIII on the third
5. Tape the single strand end of one of your
fragments to a complementary single strand
end of your partner
1.
2.
Observe Which restriction enzyme produced the
most pieces and which the fewest
Evaluate How well did your model represent the
actual process of using restriction enzymes to cut
DNA. Contrast the length of your model to the
actual length of a DNA molecule