Introduction to Genetics
Dr Narazah Mohd Yusoff
MBBS(Mal), DCP, MMed
Haem.(Lond)
Director,
Human Genome Center.
Introduction
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Molecular biology techniques – revolutionized
diagnosis and management
Major impact on all specialties, advances
ahead of therapeutic developments
Haematology – first to embrace
Hb, chromosomal rearrangements, growth
factors, oncogenes, molecular therapeutics
The History of Modern
Genetics
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Mendel and basic genetic principles
Modern era of genetics
Mendel and basic genetic
principles
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Austrian monk, Gregor Mendel (18221884)
Single-handedly
Proposed : parent plants always had 2
“factors”, but only 1 :”factor” from each
parent passed on to each individual of
the next generation
Today, Mendel’s “factors” - genes
Modern era
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1910
1949
1953
1970
1980
1985
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Fruit fly, TH Morgan
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L Pauling – “molecular disease”
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Watson & Crick – “double helix”
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PCR, Kary Mullis
Studying DNA in people
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“It runs in the family”
How to prove certain conditions are
genetic?
Twin studies
Determining which genes are involved
Picking a control group
Impact of Human Genome Project
How does DNA affect you?
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Ethics - scientists working on reading
and manipulating information in DNA.
Their discoveries – many ethical
dilemmas
You are the parent
You and your husband have been trying to have
a girl for 15 years.
Instead, you have had 5 boys. At a very early
stage of pregnancy, you discover another boy is
on the way. If there was a genetic treatment to
change the gender of your fetus, would you use
it?
You are the Doctor
Your patient has a f/hx of colon cancer,
Otherwise she is physically normal.
She requests genetic tests. Results indicate that
there is a 15% chance she will develop colon
cancer in the next 20 years. It is your job
to advise your patient. You do not want to
alarm your patient about these inconclusive
results. Do you tell her that she is at risk?
You are the patient
When you were just a baby, your grandfather
died of Huntington's disease. Huntington's is a
debilitating mental disease that develops in
middle age and often results in death before
the age of 50 and there is no known cure for
the disease. You know that there is a chance
that you carry the Huntington's gene. There is a
simple genetic test that can determine whether
you are a carrier. Do you get tested? or is
ignorance bliss?
You are the Judge
You have just finished listening to the closing
arguments of a trial and you go to your
chambers to make a decision. The attorneys for
the insurance company argued that genetic
profiles should be available for review by
insurance companies saying that insurance
companies have a right to know about the preexisting conditions of their clients, including the
genetic pre-disposition to develop a disease.
You are the judge-1
If insurance companies remain ignorant of
genetic profiles, individuals without genetic
flaws will be forced to subsidize the cost of
those who develop genetic diseases.
The attorneys challenged the insurance
company's argument and asserts that genetic
information is private. The 5th amendment
protects the privacy of all individuals including
genetic privacy.
You are the judge - 2
If genetic information was made public,
individuals with genetic flaws
would face discrimination from insurance
companies and employers. You ponder the
evidence for several hours. Now it is time
to make a decision. Do you rule in favor of the
insurance company or the other?
You are the voter - 1
It is 2010. You are preparing to vote
on a new bill that requires all citizens to provide
blood samples to the local police department.
The samples will be used to create a database
of genetic information. The police will use the
database to identify and apprehend crime
suspects and clear innocent people of crime
charges. Proponents of the bill argue that it is
an essential step in the war against crime.
You are the voter - 2
Opponents claim that the information will
be misused and that genetic information
should remain private. Do you vote
in favor of the new bill?
GENETIC ELEMENTS
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Structures that contain genetic information
Chromosomes carry - information req. for life
Non-chromosomal elements: mitochondria &
chloroplast DNA, plasmids, viruses,
transposable elements.
Mitochondria and chloroplasts - contain DNA,
but cannot exist independently.
Plasmids – circular, ds DNA, have own origin
of replication, don’t exist extracellularly, may
confer a selective advantage (e.g. antibiotic
resistance).
GENETIC ELEMENTS
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Viruses - non-cellular genetic elements, enlist
specific cells for their own replication, consist
of protein & nucleic acid (ds/ss DNA or RNA).
Transposable elements –1st identified in
maize
Replicate as part of another genetic element
capable of moving from site to site.
Transposable elements prove - genetic
material not stable, fluidic
DNA STRUCTURE
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DNA double stranded, and the strands:
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are held together by hydrogen bonds form specifically
between A and T and G and C residues.
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have sequence of bases on one strand of the DNA
molecule (say TAGGCTAG), only one possible partner
(ATCCGATC), sequences called complementary.
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have a polarity; one end is - the 5' end, the other - 3' end,
strands run in opposite directions, i.e. antiparallel.
DNA Structure
The structure of DNA is illustrated by a right handed
double helix, with about 10 nucleotide pairs per helical
turn. Each spiral strand, composed of a sugar
phosphate backbone and attached bases, is connected
to a complementary strand by hydrogen bonding (noncovalent) between paired bases, adenine (A) with
thymine (T) and guanine (G) with cytosine (C). Adenine
and thymine are connected by two hydrogen bonds
(non-covalent) while guanine and cytosine are
connected by three. This structure was first described
by James Watson and Francis Crick in 1953.
Components of DNA
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DNA – polymer, monomer units - nucleotides,
and the polymer is known as a
"polynucleotide."
Each nucleotide - 5-carbon sugar
(deoxyribose), a nitrogen containing base
attached to the sugar, and a phosphate
group.
Four different types of nucleotides, differing
only in the nitrogenous base. The nucleotides
are given one letter abbreviations
Deoxyribose Sugar
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The deoxyribose sugar of the DNA backbone
has 5 carbons and 3 oxygens.
The carbon atoms are numbered 1', 2', 3', 4',
and 5' to distinguish from the numbering of
the atoms of the purine and pyrmidine rings.
The hydroxyl groups on the 5'- and 3'carbons link to the phosphate groups to form
the DNA backbone.
Deoxyribose lacks an hydroxyl group at the
2'-position when compared to ribose, the
sugar component of RNA.
Components of DNA
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A - adenine
G - guanine
C - cytosine
T - thymine
Purine Bases
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Adenine and guanine - purines.
Purines - the larger of the two types of
bases found in DNA.
The 9 atoms that make up the fused
rings (5 carbon, 4 nitrogen) are
numbered 1-9. All ring atoms lie in the
same plane.
Pyrimidine Bases
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Cytosine and thymine - pyrimidines.
The 6 atoms (4 carbon, 2 nitrogen) numbered 1-6. Like purines, all
pyrimidine ring atoms lie in the same
plane.
Nucleotides
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Nucleotide - nucleoside with one or
more phosphate groups covalently
attached to the 3'- and/or 5'-hydroxyl
group(s).
Nucleosides
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A nucleoside is one of the four DNA bases
covalently attached to the C1' position of a
sugar.
Sugar in deoxynucleosides - 2'-deoxyribose.
Sugar in ribonucleosides - ribose.
Nucleosides differ from nucleotides - they lack
phosphate groups.
The 4 different nucleosides of DNA deoxyadenosine (dA), deoxyguanosine (dG),
deoxycytosine (dC), and (deoxy)thymidine
(dT, or T).
NUCLEIC ACIDS (DNA and
RNA)
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DNA = deoxyribonucleic
acid.
The sugars in DNA
contain a 2' hydrogen
DNA is chemically
stable
DNA functions - carrier
of genetic information
(usually
DNA contains the bases
adenine (A), guanine
(G), cytosine (C), and
thymine (T)
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RNA = ribonucleic acid.
Sugars in RNA contain a
2' hydroxyl group
RNA is less stable than
DNA (dt the presence of
the 2' hydroxyl group)
RNA - carrier of genetic
information
RNA contains the bases
adenine (A), guanine
(G), cytosine (C) and
uracil (U)
WORKING WITH NUCLEIC
ACIDS
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DETECTION
PURIFICATION OF DNA
GEL ELECTROPHORESIS
DNA SEQUENCING
CUTTING AND SPLICING OF DNA
PCR = POLYMERASE CHAIN REACTION
GENE CLONING
TRANSFORMATION/TRANSFECTION
Because both strands are copied during PCR, there is an
exponential increase of the number of copies of the gene.
Suppose there is only one copy of the wanted gene before
the cycling starts, after one cycle, there will be 2 copies,
after two cycles, there will be 4 copies, three cycles will
result in 8 copies and so on.
PCR
Requires:
1. DNA template to be amplified
2. Knowledge of the boundaries (i.e. one must
know the sequence of the regions flanking
the region to be amplified)
3. Two primers - short, single-stranded DNA
complementary to each end of the DNA to
be amplified
4.
Substrate dNTPs
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A heat-stable DNA polymerase to construct
the DNA
PCR
A PCR cycle- repeated 20-30 times to
synthesize copies of the target DNA
exponentially.
 Each cycle consists of three steps:
1. Heat denaturation of DNA to separate the
target DNA into its component strands
2.Cooling to hybridize primers to the target
DNA
3.DNA polymerization (extension) to make
copies of the DNA
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PCR
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Uses:
Amplification of DNA allows it to be detected
easily
DNA fingerprinting - forensics investigations
for identification of individuals e.g. VNTRs =
Variable Number of Tandem Repeats eukaryotic DNA contains short, non-coding
sequences that vary in length from organism
to organism. These regions can be amplified
by PCR and their lengths determined - a "bar
code" for an individual
Verification of PCR product
on agarose gel
FISH
Microarray
Microarray Technology
A new way of studying how large numbers of genes interact
with each other and how a cell's regulatory networks control
vast batteries of genes simultaneously. The method uses a
robot to precisely apply tiny droplets containing functional
DNA to glass slides. Researchers then attach fluorescent
labels to DNA from the cell they are studying. The labeled
probes are allowed to bind to complementary DNA strands
on the slides. The slides are put into a scanning microscope
that can measure the brightness of each fluorescent dot;
brightness reveals how much of a specific DNA fragment is
present, an indicator of how active it is.
The Human Genome Project
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Please refer to Primer Slides
Points to Ponder
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The Human Genome Project - why is it
important? How and will it change
medicine forever?
DNA and medicine - affects everything
including drugs
How DNA works - sick?
DNA & society - DNA & forensics, ethics
of genetics and gene therapy
Biotechnology: The present and future
Molecular biology useful in many fields. DNA technology
utilized in solving crimes, also allows searchers to produce banks
of DNA, RNA and proteins, while mapping the human genome.
Tracers are used to synthesize specific DNA/ RNA probes,
essential to localizing sequences involved in genetic disorders.
Genetic engineering, new proteins synthesized, can be
introduced into plants or animal genomes, producing a new type
of disease resistant plants, capable of living in inhospitable
environments, introduced into bacteria, these proteins have also
produced new antibiotics and useful drugs.
Techniques of cloning generate large quantities of pure
human proteins, which are used to treat diseases like
diabetes. In the future, a resource bank for rare human
proteins or other molecules is a possibility. For instance,
DNA sequences which are modified to correct a
mutation, to increase the production of a specific protein
or to produce a new type of protein can be stored . This
technique will be probably play a key role in gene
therapy.
Summary
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DNA: Life's Instruction Manual
DNA is in every cell of your body
DNA is Information- needed to
construct and operate a human body.
(type your name as have it converted
into a DNA alphabet)