Darwin’s Tea Party
The Biological Revolution: DNA and
Modern Genetics
Winter 2009
After Mendel
• Gregor Mendel (1822-1884) had discovered the
basic mechanisms of heredity.
• His discoveries also strongly suggested physical
or material particles were responsible for the
transmission and expression of these hereditary
characteristics.
The Discovery of DNA
In 1951 James Watson (1928) and Francis Crick (1916- )
discovered the structure of
the DNA molecule -
Deoxyribonucleic Acid
In this famous photograph Watson (right) and Crick (left)
demonstrate a model of the DNA molecule.
The Discovery of DNA
DNA was soon shown to be the mysterious material
particle sought for since Mendel’s discoveries.
The Discovery of DNA
Hi Mom!
DNA exists in
the nucleus of
almost every cell
in the body,
beginning from
day 1 when you
were just an
embryo.
Cross section of skin, showing skin cells.
DNA is inside
the nucleus of a
cell, within its
chromosomes
The DNA molecule is structured in a
“double helix” shape (like two spiraling
staircases).
One helix is connected to another by base
pairs – shown here as “A”, “T”, “C”, “G”.
DNA Base Pairing Rules
Base pairing rules
The base pairs, though, must
connect following the basepairing rules so that “A”
connects only with “T” and “C”
with “G”.
A Japanese molecule
DNA sequences
A DNA sequence is simply the
order of base pairs along the DNA
double spiral.
In this case, we note the sequence
“T-A” “C-G”
DNA and Genes
What is a gene?
A gene is thus a segment of
DNA containing varying
lengths of DNA base pair
sequences (T-A, C-G, G-C,
T-A, etc…).
Genes and Proteins
• Different DNA sequences (genes)
“spell out” different kinds of proteins.
• Proteins are key ingredients helping to
make all sorts of cells and cell
functions from skin cells, to hair cells,
to blood products, to various enzymes,
to … you name it.
• In this way DNA really is a blue print
for how to make the proteins &
enzymes that go on to make the traits
of an entire body.
Actually, the route from DNA sequence to protein
is a bit more complicated. First the DNA sequence
spells out a certain type of amino acid and that
then helps produce a certain type of protein.
Genes and Traits
• Thus genetic traits, whether physical or mental
can be traced back to DNA sequences.
• This is true for “normal traits”, e.g. for hair
colour, eye colour, etc… as well as for
“abnormal traits”, such as some genetic diseases.
• Humans have 23
pairs of
chromosomes,
receiving one
pair from each
parent.
• Genes are
located in
particular
locations and
regions of the
chromosomes.
Human Genome Project
• Thanks to the Human
Genome Project and
other endeavours to
“map” the genetic code,
we can now detect many
genetic anomalies
responsible for genetic
diseases in humans.
• Here, in specific locations
of chromosomes 13 and
17, are the BRCA1 and
BRCA2 mutations,
responsible for some
hereditary forms of breast
cancer.
Genes and Traits
In this example, the genetic
disease sickle cell anemia
can be traced back to a
single genetic “spelling
mistake” in the genetic
sequences contained in the
upper part of chromosome
11:
Genetic Engineering
Genetic Engineering
• Genetic engineering involves modifying sections
of the genetic code (gene sequences) of an
organism.
• This can be done by cutting, copying, changing
or inserting desired gene sequences in the
genetic code.
• Inserting of gene sequences is often done
through viruses and bacteria.
Genetic Engineering
Genes can control certain traits;
as in flower colour in this
example.
Genetic engineering: Using bacteria and viruses
Of course, we don’t always
associate bacteria and
viruses with helpful effects!
Here, for example, are two
unhelpful bacteria, the
Tobacco Mosaic Virus and
Human Immunodeficiency
Virus (HIV) which produces
AIDS.
The T4 bacteriophage is a
virus which attack the E. coli
bacteria.
Applications of genetic engineering
Gene
Therapy
Genetic engineering
techniques can be used for
altering genetic sequences
responsible for genetic
diseases. This is called gene
therapy.
In this case, missing
sequences causing Cystic
fibrosis can be inserted into
the genetic code of a CF
patient using a virus as
delivery vehicle.
Genetic engineering of pharmaceuticals
Here the gene for producing insulin is
taken from a human chromosome and
inserted into a bacteria’s plasmid (a single
ringed chromosome). This plasmid with
the human insulin gene can then be used
to produce insulin to treat certain forms
of diabetes.
This is one example of how genetic
engineering techniques can be used to
create pharmaceuticals or medicines.
Genetically modified foods
But what if we could
change the genetic blue
print – the genetic
sequences that ultimately
make up life?
Genetically Modified Foods (GMFs)
Scientists can alter genes by cutting out undesired and inserting desired sequences. In this
case a gene from a bacteria called Bt which acts like an insecticide is being inserted into the
genetic code of a corn plant. The corn will thus contain this built in insecticide.
Catfish anyone?
http://mathgeeklife.blogspot.com/2007/11/genetic-engineering.html
Genetic engineering of humans?
Fears of genetic
engineering often
go back to the
Frankenstein story.
Applications of Genetic Technology
Thus, many applications of genetic technology exist,
including:
– Criminal forensics
– Medical Diagnostics
– Genetically Modified Foods/Organisms (GMFs/GMOs)
– Gene Therapy
– Genetic Cloning
– Embryonic and Stem cell research
– Tracing evolutionary history and linkages
– Much, much more!
Applications of Genetic Technology
• However, all of these technologies also confront
us with serious potential for abuse and misuse.
• The same techniques that can heal can also be
used to modify organisms in ways that may not
be beneficial to those organisms
• This includes the human organism too!