Daniel Njuguna - DAIS 2012
Assessment statements
4.4.1
4.4.2
4.4.3
4.4.4
4.4.5
4.4.6
4.4.7
4.4.8
4.4.9
4.4.10
4.4.11
4.4.12
4.4.13
Outline the use of polymerase chain reaction (PCR) to copy and amplify
minute quantities of DNA.
State that, in gel electrophoresis, fragments of DNA move in an electric
field and are separated according to their size.
State that gel electrophoresis of DNA is used in DNA profiling.
Describe the application of DNA profiling to determine paternity and
also in forensic investigations.
Analyse DNA profiles to draw conclusions about paternity or forensic
investigations.
Outline three outcomes of the sequencing of the complete human
genome.
State that, when genes are transferred between species, the amino acid
sequence of polypeptides translated from them is unchanged because
the genetic code is universal.
Outline a basic technique used for gene transfer involving plasmids, a
host cell (bacterium, yeast or other cell), restriction enzymes
(endonucleases) and DNA ligase.
State two examples of the current uses of genetically modified crops or
animals.
Discuss the potential benefits and possible harmful effects of one
example of genetic modification.
Define clone.
Outline a technique for cloning using differentiated animal cells.
Discuss the ethical issues of therapeutic cloning in humans.
Polymerase chain reaction (PCR)
 Laboratory
technique which
takes a very small
quantity of DNA
and copies all the
nucleic acids in it
to make millions
of copies of the
DNA
 Way to ensure
that enough DNA
for analysis can
be generated
Gel electrophoresis
 Laboratory technique used to separate
fragments of DNA in an effort to identify
its origin
 Enzymes used to chop up DNA strands
into fragments
 Fragments are placed into small wells in
the gel
 Gel is exposed to an electric current
 Heaviest, largest and least charged
particles do not move easily through the
gel
 Smallest, least massive and most charged
particles pass through the gel to the other
side easily
 Intermediate particles are distributed in
between
 In the end, the fragments leave a banded
pattern of DNA to be used in DNA
profiling
DNA profiling
 Process of matching an
unknown sample of DNA with a
known sample to see if they
correspond
 Also referred to as DNA
fingerprinting
 If, after separation by gel
electrophoresis, the pattern of
bands formed by two samples of
DNA fragments are identical, it
means that both came from the
same individual
 If the patterns are similar, it
means that the two individuals
are most probably related
Applications of DNA profiling
 Parentage testing
 e.g. resolving paternity
disputes
 Forensic investigations
 e.g. match suspects
samples & those found at
the scene of crime
 Ecosystems forensic
 e.g. birds migrating
patterns & nesting habits
 Evolution credibility
 e.g. matching fossil
samples with those of
organisms living today
Paternity Investigation
 Determine who is the biological father
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of the child, male 1 or male2
The DNA fragments in the child comes
from the mother and father
A band present in the child must come
either from the mother or from the
father
Compare male 1 with the child & the
mother then male 2 with the child &
the mother.
The bands on the child's fragments are
either found on the mother or the
male1.
Therefore Male 1 is this father of this
child.
Forensic Investigation – Case 1
 A specimen of DNA is taken from the
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victim or the crime scene
DNA samples are taken from the 3 suspects.
The bands are compared to associate the
suspects but to eliminate the victims DNA
from the specimens
Of the 3 suspects, who is likely to have been
at the scene of crime?
the bands on the specimen are matched by
the bands on the Suspect 1, therefore
Suspect 1 was present at the crime scene
Is this evidence sufficient to convict the
suspect?
The law will still require to prove a crime
was committed and then that Suspect 1
really committed the crime
Forensic Investigation – Case 2
 Sexual assault has been
committed and two
suspects are under
investigation
 DNA profile was carried
out and the result are
shown in the opposite
diagram
 From the DNA profile, who
of the two suspects
committed the assault?
 The two bands visible on
the evidence (sperm DNA)
matches the DNA sample
from suspect 1
TOK Aspects
 How would you feel if you
were to find out from DNA
profiling that your father with
whom you’ve lived with for 18
years was not your biological
father?
 What effect would such a
result have on the
relationships between
siblings or between spouses?
 What kind of emotions might
someone feel after spending
18 years in prison, and then
being freed thanks to a DNA
test?
The Human Genome Project
 Commitment by world’s
scientific community to
determine the location &
structure of all genes in
human chromosomes
 Started in 1990 & by 2003,
99.9 % of the work of
sequencing human DNA was
completed
 It involved sequencing 3 x 109
base pairs in human DNA
then mapping the genes i.e.
listing & finding the locus of
each human gene
Outcomes of the sequencing of
the complete human genome
 improved understanding of genetic
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diseases because more disease causing
genes are now known
production of medicine based on DNA
sequences to cure diseases & or remove
disease causing genes through genetic
engineering
to determine fully which genetic diseases
any individual is prone to & genetic
screening can lead to preventive
medicine
it provides more information about
evolutionary paths by comparing
similarities & differences in genes
between species
research into a particular disease now
can focus on only the gene(s) that are
relevant to the disease
TOK Aspects
 The human genome project
maps the DNA sequence of
human and could be seen as a
recipe of what it is to be
human.
 This is a “reductionist view”
which does not account for
complexity of life stemming
from interactions between our
genes & the environment
 What does the sentence, “We
are all the same; we are all
different,” mean?
 Can one genetic group be
considered genetically superior
to another?
Gene transfer
 Technique of taking a gene
out of one organism (donor)
and placing it in another
organism (host)
 When genes are transferred
between species, the amino
acid sequence of polypeptides
translated from them is
unchanged because the
genetic code is universal.
 e.g. cold resistant gene from
arctic fish is transferred to
tomatoes to make them more
resistant to cold and frost
 Proteins used by fish to resist
icy temperature of arctic
waters are now produced by
the modified tomato
General technique for gene transfer
Basic technique used for gene transfer
 Preparing a vector for the transferred
gene
 Plasmids (small circular DNA
molecules) from bacteria are used as
vector to carry the desired gene into
a host cell.
 Plasmids are removed from a
bacterium & cut using restriction
enzyme (endonuclease) leaving
complementary 'sticky ends' of
unattached hydrogen bonds in the
plasmid
 Obtaining the gene for transfer
 DNA containing gene of interest is
isolated from the donor organism
 Restriction enzymes are used to cut
out the useful gene that is to be
transferred leaving the 'sticky ends'
of unattached hydrogen bonds
 Preparing a recombinant DNA
 recombinant plasmid is used as a vector to
carry the desired gene into a host cell
 Gene of interest is placed inside the open
plasmid using DNA ligase (i.e. gene
splicing) to produce a recombinant
plasmid
 Recombinant plasmid is re-inserted into
the bacterium
 Isolation of transformed cells
 Bacterium allowed to grow and
proliferate, it expresses the desired gene
by synthesizing whatever protein the gene
codes for
 the bacterium is used to insert the DNA
carrying the foreign desired gene into the
chromosome of a host cell
 Host cells are grown in a culture medium
 An organism is generated from a cell
clone & all of its cells carry the desired
gene & may express it as a new trait
Genetically modified organisms (GMOs)
 Genetically modified
(GM) crops & animals
are called genetically
modified organisms
(GMOs) or transgenic
organisms.
 Their genetic material
has been changed to
include specific genes,
usually from another
species
 Examples of transgenic
organisms in use today
includes: tomatoes,
corn, rice, sheep, cow &
mice
Uses of transgenic organisms (genetically
modified crops & animals).
Transgenic organism
Current use of transgenic organism
Pest Resistant Corn
Produce toxins to particular insects hence reducing use
of insecticides & increasing yield
Tomatoes
Transgenic tomato plants carry the gene for salt
tolerance, frost tolerance or to ripen without becoming
soft hence keep for long
Golden Rice
transgenic rice contains the gene for the manufacture of
beta-carotene used by the body to make retinol
essential for normal vision
Sheep
Transgenic sheep produce human clotting factor (factor
IX) in milk which is isolated & used by haemophiliacs
Cow
genetically modified cows contain human genes for
making medically important proteins e.g. insulin &
growth hormone)
Potential benefits of genetic modification
 GMO results in increased yield thus
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providing more food in regions
where there is food shortage
Yields of crops with specific dietary
requirement such as vitamins and
minerals
Crops that do not spoil so easily
during storage, thus economic
benefits
GM animals produce proteins
required for medical purposes &
higher meat yields
less pesticides & fertilizers needed so
reduces environmental impact
expands world’s productive farmland
& reduces the need to clear
rainforests to grow crops
Possible harmful effects of genetic modification
 Modified genes may be released into
natural environment where they
may affect food chains resulting in
reduction in biodiversity
 GM food may affect consumers
causing health risks such as
allergies
 Producing GM foods is unfair to
smaller farmers who cannot
compete with large scale farmers
 long-term effects of GM are
unknown
 risk of cross-pollination producing
“supper plants” which out-compete
naturally occurring varieties
 There are risk s of long-term
contamination of soil
Potential benefit and possible harm of one named
example of gene transfer between species
 Gene transfer details
 Bt gene transferred from bacterium (Bacillus
thuringiensus) to maize
 specific benefit
 corn borer (insect pest) killed by Bt toxin produced by
maize plant thus increasing crop production
 less pesticides (chemicals) are needed so better for
environment due to less negative impacts
 specific harmful effect
 non-target insects may be killed by Bt toxins as well
 risk of cross-pollination may introduce Bt gene to
unintended species thus producing super weeds
Clones and cloning
 A clone is a group of
genetically identical
organisms or a group of
cells derived from a single
parent cell.
 Cloning is producing
identical copies of genes,
cells or organisms
 Producing copies of an
organism is called
reproductive cloning
while producing cells,
tissues or organs for
treating patients is called
therapeutic cloning.
Technique for cloning using differentiated animal cells
Technique for cloning using differentiated animal cells
1.
2.
3.
Somatic cell from donor
sheep udder was
collected and cultured
Unfertilized egg cell
collected from another
sheep & nucleus
removed
Using a zap of electrical
current, the egg cell and
the nucleus from the
cultured somatic cell
were fused together
New cell developed in
vitro and started to form
an embryo
5. Embryo placed in the
womb of a surrogate
mother sheep
6. Embryo developed
normally
7. Dolly was born and
presented as a clone of
the original donor sheep
This is Known as
reproductive cloning
4.
Therapeutic cloning in humans
 Therapeutic cloning involves
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creation of an embryo to supply
embryonic stem cells for medical
use & stem cell research
The technique used is same as the
one used for Dolly
Human embryos are produced &
allowed to grow into a blastocyst
(hollow ball of cells) which is broken
open & the stem cells are cultured
Therapeutic cloning aims at cell
therapy where diseased cells are
replaced with healthy ones
Cell therapy is used for patients
suffering from; leukemia,
Parkinson’s disease, skin burn &
growing new corneas for people with
visual impairment.
Ethical issues of therapeutic cloning in humans
 Is it ethically acceptable to
generate a new human embryo
for the sole purpose of medical
research?
 Religious groups belief that
every embryo contains a ‘soul’.
Should we destroy a ‘soul’ to safe
an individual’s life whose destiny
is death?
 Many scientists doubt the
existence of a ‘soul’ since a ‘soul’
can not be observed or
measured and hence there is no
data - based evidence of its
existence. Is it ethical to deny a
cancer or diabetic patient
treatment on the basis of saving
a ‘soul’ who’s existence is
uncertain?
Ethical issues of therapeutic cloning in humans
Arguments for:
Arguments against:
 Cell therapy is used to treat
 There are fears it may lead to
patients with; leukemia,
Parkinson’s disease, sever skin
burns etc. thus saving lives &
reducing pain;
 Embryos left over from IVF
treatment or those that have
stopped developing could be
used for treatment instead of
being destroyed;
 Stem cells are taken before the
embryos develop nerve cells so
they can’t feel pain;
 Risk of tissue rejection during
tissue transplant reduced.
reproductive cloning & if
embryos are not destroyed they
will develop into a clone of the
adult;
 Use of embryonic stem cells
involves creation & destruction
of human embryos;
 Embryonic stem cells are
capable of repeated cell division
& may turn into tumours;
 Every human embryo is a
potential human being & should
be given a chance of developing.
Revision Questions
 (a) Outline the use of
polymerase chain reaction
(PCR) to copy and amplify
minute quantities of DNA.
[2]
 (b) Outline some of the
outcomes of the
sequencing of the human
genome.
[3]
 (c) Outline a basic
technique for gene transfer.
[6]
 (d) Explain the methods
and aims of DNA profiling.
[8]
 (e) Using a named
example, discuss the
benefits and harmful
effects of genetic
modification.
[9]
 (f) Genetic modification
involves the transfer of
DNA from one species to
another. Discuss the
potential benefits and
possible harmful effects of
one example of genetic
modification in a named
organism.
[9]