UNIT 14 APPLICATION OF GENE TECHNOLOGY
UNIT 14: APPLICATION OF GENE TECHNOLOGY
Key Unit Competence
Evaluate how gene technology is applied in areas of medicine, forensic science and
agriculture
Learning objectives
By the end of this unit, I should be able to:
– Define the term bioinformatics.
– Outline the role of bioinformatics following the sequencing of genomes, such as
those of humans and parasites, e.g. Plasmodium. (Details of the methods of DNA
sequencing are not required).
– Explain the advantages of producing human proteins by recombinant DNA
techniques. (Reference should be made to some suitable examples, such as
insulin, factor VIII for the treatment of haemophilia and adenosine deaminase
for treating severe combined immunodeficiency (SCID).
– Outline the advantages of screening for genetic conditions. (Reference may
be made to tests for specific genes such as those for breast cancer, BRCA1 and
BRCA2, and genes for haemophilia, sickle cell anaemia, Huntington’s disease
and cystic fibrosis).
– Outline how genetic diseases can be treated with gene therapy and discuss
the challenges in choosing appropriate vectors, such as: viruses, liposomes and
naked DNA, (Reference may be made to SCID, inherited eye diseases and cystic
fibrosis).
– Explain the significance of genetic engineering in improving the quality and
yield of crop plants and livestock in solving the demand for food in the world
e.g. Bt maize, vitamin A enhanced rice (Golden rice TM) and GM salmon.
– Outline the way in which the production of crops such as maize, cotton, tobacco
and rape seed oil may be increased by using varieties that are genetically
modified for herbicide resistance and insect resistance.
– Explain the ethical and social implications of using genetically modified
organisms (GMOs) in food production.
– Interpret a chart on the stages involved in the production of insulin by bacteria.
– Analyse the application of gene technology in agricultural modernisation.
– Research the benefits, hazards and implications of gene technology.
– Appreciate the application of gene technology in medicine, and forensic science
such as the detection of crimes e.g. rape, murder, and paternity disputes.
– Appreciate the application of gene technology in agriculture through the
improvement of crop varieties and animal breeds.
Introductory activity14.1
Observe the plants and animals below and carry out the following activity:
1. Discuss the reasons why the above crops(A and B) and animals (C and D)
present some differences.
2. Is there any benefits of having different varieties of organisms belonging to
the same species?
Techniques used by genetic engineers have been seen in unit 13. What can be
done with these techniques? By far most numerous applications are still as research
tools, and those techniques are helping geneticists to understand complex genetic
systems. Despite all of those types, genetic engineering still has very few successful
commercial applications, although these are increasing each year. The applications
so far can usefully be considered in three groups.
– Gene products using genetically modified organisms (usually microbes) to
produce chemicals, usually for medical or industrial applications.
– New phenotypes using gene technology to alter the characteristics of
organisms (usually farm animals or crops).
– Gene therapy using gene technology on humans to treat a disease.
The biggest and most successful kind of genetic engineering is the production of
gene products. These products are of; medical, agricultural or commercial value.
The table below shows some examples of genetically engineered products that are
already available.
Table 14.1 Examples of genetically engineered products and their uses
14.1 Bioinformatics
Activity 14.1
Using book or internet to search information about the importance of
Bioinformatics. Thereafter; discuss how the bioinformatics contribute to the
sequencing of genomes. In your discussion focus on human and parasite
genomes like Plasmodium.
Bioinformatics is the collection, processing and analysis of biological information
and data using computer software. In other words, it is the branch of biology that
is concerned with the acquisition, storage, and analysis of the information found in
nucleic acid and protein sequence data. Bioinformatics combines biological data
with computer technology and statistics. It builds up databases and allows links to
be made between them. The databases hold gene sequences of complete genomes,
amino acid sequences of proteins and protein structures.
UniProt (universal protein resource) holds information on the primary sequences
of proteins and the functions of many proteins, such as enzymes. The search tool
BLAST (basic local alignment search tool) is an algorithm for comparing primary
biological sequence information, such as the primary sequences of different proteins
or the nucleotide sequences of genes. Researchers use BLAST to find similarities
between sequences that they are studying and those already saved in databases.
When a genome has been sequenced, comparisons can be made with other known
genomes. For example, the human genome can be compared to the genomes of
the fruit fly, Drosophila, the nematode worm, or the malarial parasite, Plasmodium.
All the information about the genome of Plasmodium is now available in databases.
This information is being used to find new methods to control the parasite. For
example, being able to read gene sequences is providing valuable information in
the development of vaccines for malaria.
Application 14.1
1. What do you understand by the term bioinformatics?
2. Explain the role of bioinformatics following the sequencing of genomes, in
controlling and prevention of malaria.
14.2 Production of human proteins by recombinant DNA technology
Activity 14.2
Observe the figure below, analyse it and do the following:
1. What does the above figure represent?
2. Using textbook or internet, interpret what happens in the stages A to E.
Recombinant DNA technology brought about a complete revolution in the way
living organisms are exploited. By transferring new DNA sequences into microbes,
plants, and animals, or by removing or altering DNA sequences in the endogenous
genome, completely new strains or varieties can be created to perform specific
tasks. One of the earliest commercial applications of gene manipulation was the
production of human therapeutic proteins in bacteria. Not surprisingly, the first
such products were recombinant versions of proteins already used as therapeutics:
human growth hormone and insulin. Prior to the arrival of genetic engineering,
human growth hormone was obtained from pituitary glands removed from cadavers
and the insulin was extracted from the pancreas of pigs or cattle.
Production of Insulin
This hormone can be produced by genetically modified bacteria and has been
in use since 1982. The human insulin gene is inserted into bacteria, which then
secrete human insulin. The human insulin produced in this way is purer than insulin
prepared from pigs or cattle that was used before, which sometimes provokes
allergic reactions owing to traces of ‘foreign’ protein. The Genetically Modified(GM)
insulin is acceptable to people with a range of religious beliefs who may not be
allowed to use insulin from cows or pigs. The main advantage of this form of insulin
is that there is now a reliable supply available to meet the increasing demand. The
chart below summarises stages involved in the production of insulin by bacteria
Figure 14.2 Producing insulin from genetically modified bacteria.
There were problems in locating and isolating the gene coding for human insulin
from all of the rest of the DNA in a human cell. Instead of cutting out the gene from
the DNA in the relevant chromosome, these are steps involved in human insulin
production:
– Researchers extracted mRNA for insulin from pancreatic β cells, which are the
only cells to express the insulin gene. These cells contain large quantities of
mRNA for insulin as they are its only source in the body.
– The mRNA was then incubated with the enzyme reverse transcriptase which
comes from the group of viruses called retroviruses. As its name suggests, this
enzyme reverses transcription, using mRNA as a template to make singlestranded
DNA.
– These single-stranded DNA molecules were then converted to doublestranded
DNA molecules using DNA polymerase to assemble nucleotides to
make the complementary strand.
– The genetic engineers now had insulin genes that they could insert into
plasmids to transform the bacterium Escherichia coli.
– When the bacterial cells copy their own DNA, they also copy the plasmids and
the donor genes that plasmids carry. After the cells have grown into colonies,
on an industrial scale in large fermenters insulin is extracted from the bacteria.
14.3 Genetic technology applied to medicine and forensic science
Activity 14.3
Using books or internet search and summarize information about genetic
technologies applied to medical and forensic sciences
1. Discuss about the social and ethical considerations of using gene
testing and gene therapy in medicine.
2. Interpret how gene technology is important in detection of crimes
(such as; rape, theft, and murder) and solving parenthood disputes.
14.3.1 Genetic screening
Genetic screening is the detection of mutations known to be associated with
genetic disorders before they manifest themselves in an individual. This can be done
in adults, in a foetus or embryo in the uterus, or in a newly formed embryo produced
by in-vitro fertilization. For example, an adult woman with a family history of breast
cancer may choose to be screened for the faulty alleles of the genes Brca-1 and Brca-
2, which considerably increase an individual’s chance of developing breast cancer. If
the results are to be positive; the woman may choose to have her breasts removed
(elective mastectomy) before such cancer appears.
Genetic disorders in the human foetus can also be detected using genetic screening
of embryonic cells found in the amniotic fluid during gestation. Such prenatal screens
are available for haemophilia, phenylketonuria, cystic fibrosis, and Duchenne’s
muscular dystrophy. Couples with a family history of genetic disorders who are
at risk of passing mutations on to their offspring are offered genetic counselling
to better prepare for the birth of a child. The most common vectors that are used
to carry the normal alleles into host cells are viruses (often retroviruses) or small
spheres of phospholipid called liposomes.
14.3.2 The ethics of genetic screening
Many people believe that the law is allowing too much, while others think that it
should allow more. For instance, in some countries, the law allowed an embryo
screening for a genetic disease; also some countries allow a successful transplant of
tissue from one person to another. But the law does not allow the addition of an allele
to an egg, sperm or zygote. Other countries have different attitudes and regulations.
For example, a foetus can now be screened for a genetic disease while in the uterus,
using amniocentesis or chorionic villus sampling. From this screening parent can
decide to terminate her pregnancy if the embryo is found to have a genetic disease.
Some parents have decided to terminate pregnancies simply because the child is not
the sex that they want. Pre-implantation genetic diagnosis (PGD) is the technique
that involves mixing the father’s sperm with the mother’s eggs in a dish (In vitro
procedure). The PGD has been also used to select the sex of the embryo that is
chosen to be implanted. Many people think that this sex pre-selection, as it is called,is totally unethical.
14.3.3 Treatment of genetic diseases by gene therapy
Gene therapy is the introduction of genes into suffering individual for therapeutic
purposes. It holds great potential for treating disorders noticeable to a single
defective gene. The first successful gene therapy performed was about the rare
genetic disorder known as severe combined immunodeficiency (SCID). The defect
in SCID involves the inability to make an enzyme, adenosine deaminase (ADA)
which is vital for the functioning of the immune system. These enzymes are made
by a genetically modified; insect larva, the cabbage looper moth caterpillar. This
enzyme is administered to patients while they are waiting for gene therapy or when
gene therapy is not possible. The work on SCID has led to increasingly successfulgene therapies in the last few years, including the followings:
a. Inherited eye diseases
Inherited eye diseases called Leber congenital amaurosis is a form of hereditary
blindness that primarily affects the retina, which is a specialised tissue at the back of
the eye that detects light and colour. People with this disorder typically have severe
vision impairment beginning at infancy. By gene therapy this condition has beenimproved.
b. Haemophilia
Haemophilia is an inherited bleeding disorder where the blood does not clot
properly. It is caused when blood does not have enough clotting factor. Genetically
modified hamster (small furry animal which is similar to a mouse) cells are used by
several companies to produce factor VIII. This protein is essential for blood clotting,
and people who cannot make it are said to have haemophilia. The human gene for
making factor VIII has been inserted into hamster kidney and ovary cells which are
then cultured in fermenters. The cells constantly produce factor VIII which is extracted
and purified before being used to treat people with haemophilia. These people need
regular injections of factor VIII which, before the availability of recombinant factorVIII, came from donated blood.
c. Cystic fibrosis
Cystic fibrosis which is a genetic disorder in which abnormally thick mucus
is produced in the lungs and other parts of the body, is also treated using gene
therapy. Cystic fibrosis is caused by a recessive allele of the gene that codes for a
transporter protein called CFTR (cystic fibrosis transmembrane conductance
regulator). This protein is found in the cell surface membranes of cells in the alveoli
and allow chloride ions (Cl-) to pass out of the cells. The recessive allele codes for a
faulty version of this protein that does not act properly as a chloride ion transporter.
If the normal dominant allele could be inserted into cells in the lungs, the correct
CFTR should be made. In theory this should happen but in practice, there have beenproblem of getting the allele into the cell.
Figure 14.3: Diagram showing the processes involved in the infection of cystic fibrosis in cell lining of lungs
Note that:
There were different trials of gene therapy using different vectors like liposomes and
viruses which were not successful. DNA also has been inserted directly into tissues
without the use of any vector. This so called naked DNA has been used in trials
of gene therapy for skin, muscular and heart disorders. The advantages of using
this method is that, it removes the problems associated with using vectors. Some
proteins are even produced by transgenic animals. Sheep and goats have been
genetically modified to produce human proteins in their milk: human antithrombin
is produced by goats, this protein is used to stop blood clotting human alpha.
Antitrypsin is produced by sheep, this is used to treat people with emphysema.
14.3.4 Application of gene technology in forensic science.
Forensic science deals with the application of scientific methods and techniques
to matters under investigation by a court of law. For most people, forensic science is
synonymous with criminal investigations, but it is also used to resolve civil disputes
such as parenthood disputes.
DNA can be extracted from small sample of the cells found at the scene of the crime,for example in traces of blood, hair or saliva. In cases of rape, semen may be used.
a. Detection of crimes (Rape or murder)
Figure 14.4 Genetic fingerprint of semen or blood (from Crime scene) and the blood of suspect rapists ormurders.
b. In forensic science, DNA fingerprinting is used to match material collected at
the scene of crime to that of suspects. This diagram above( Figure 14.4 ) of the
genetic fingerprints shows semen or blood (specimen from crime scene) found
on the victim and blood samples taken from the suspect rapists or murder.
The fingerprint results show an exact match between semen or blood sample
obtained from the victim and the blood sample of suspect 2. As a result suspect2 is confirmed to be the rapist or a murderer.
c. Paternity test
In perternity tests, DNA of suspected fathers are analysed together with the one
of the child and the mother in order to find out the potential father among the
suspect fathers that has the most DNA common with the child in question. Figure
14.5 shows an example of a Restriction Fragment Length Polymorphism (RFLP) used
to determine which potential father between father 1 and 2 who is the real father of
the child (C). As it is seen on the above figure, the second father tested (F2) seems tohave more DNA in common with the child than of the first farther tested (F1).
Figure 14.5 A peternity test using the RFLP (Restriction Fragment Length Polymorphism) technique
Application 14.3
1. Identify the advantages of genetic screening.
2. Gene therapy for cystic fibrosis would be successful if only one copy of
the normal allele of the gene was successfully inserted into the cells.Explain why this is so.
14.4 Significance of genetic engineering in improving thequality and yield of crop plants and livestock
Activity 14.4
Visit an agricultural center or research stations available in the area or observe
movies and find out how gene technology is applied in the modernization of
agriculture and livestock farming in Rwanda
1. Focus on the following crops varieties: maize, cassava, irish potatoes,
beans, tomatoes, oranges, mangoes, and avocado.
2. Focus on the following animals: poultry, cattle, goats, sheep, and pigs.
3. Based on your observations, discuss how modified crops and animals
contributed in improving the quality and yield of crop plants andlivestock in Rwanda.
Scientists are working to learn more about the genomes of agriculturally important
plants and animals. For a number of years, they have been using DNA technology
in an effort to improve agricultural productivity. The selective breeding of both
livestock (animal husbandry) and crops has exploited naturally occurring mutations
and genetic recombination for thousands of years. As we described earlier, DNA
technology enables scientists to produce transgenic animals, which speeds up theselective breeding process.
14.4.1 Gene technology and agriculture
Many new products have been developed using this technology. Crops have been
genetically engineered to increase yield, hardiness, uniformity, insect and virus
resistance, and herbicide tolerance. The vast bulk of genetically modified plants
grown around the world are crop plants modified to be resistant to herbicides or
crops that are resistant to insect pests. These modifications increase crop yield. A
few crops, such as vitamin A, enhanced rice, provide improved nutrition
a. Golden rice
Golden rice is a staple food in many parts of the world, where people are poor and
rice forms the major part of their diet. Deficiency of vitamin A is a common and serious
problem; its deficiency can cause blindness. In the 1990s, a project was undertaken
to produce a variety of rice that contained carotene in its endosperm. Genes for the
production of carotene were extracted from maize and the bacterium Pantonoea
ananatis. These genes, together with promoters, were inserted into plasmids. The
plasmids were inserted into bacteria called Agrobacterium tumefaciens. These
bacteria naturally infect plants and so could introduce the genetically modified
plasmid into rice cells. The rice embryos, now containing the carotene genes, weregrown into adult plants.
This genetically modified rice is called golden rice, because it contains a lot of
yellow pigment carotene. The genetically modified rice is being bred into other
varieties of rice to produce varieties that grow well in the conditions in different
parts of the world, with the same yield, pest resistance and eating qualities as theoriginal varieties.
Figure 14.6: Normal rice (white) compared with golden rice (yellow)
b. Herbicide-resistant crops: Oil seed rape
Herbicide-resistant crops called oil seed rape or Brassica napus, is grown in many
parts of the world as a source of vegetable oil which is used as biodiesel fuel, as a
lubricant and in human and animal foods. Natural rape seed oil contains substances
that are undesirable in oil that is to be used in human or animal food. A hybrid, was
made to produce low concentrations of these undesirable substances, called canola
(Canadian oilseed low acid), and this name is now often used to mean any variety of
oil seed rape. Gene technology has been used to produce herbicide-resistant strains.
Growing an herbicide-resistant crop allows fields to be sprayed with herbicide after
the crop has germinated, killing any weeds that would otherwise compete with the
crop for space, light, water or ions. This increases the yield of the crop.
c. Insect pests-resistant plants
Another important agricultural development is that of genetically modified plants
protected against attack by insect pests. Bt maize is genetically engineered (GE)
plant that produces crystal (Cry) proteins or toxins derived from the soil bacterium,
Bacillus thuringiensis (Bt), hence the common name “Bt maize”. Bt maize plant has
revolutionized pest control in a number of countries, but there still are questionsabout its use and impact.
14.5.2 Transgenic animals.
DNA technology enables scientists to produce transgenic animals, which speeds up
the selective breeding process. Creating transgenic animals is aimed at improving
quality and productivity. For instance, to make a sheep with better quality wool, a
pig with leaner meat, or a cow that will mature in a shorter time. Scientists might, for
example, identify and clone a gene that causes the development of larger muscles
(muscles make up most of the meat) in one breed of cattle and transfer it to othercattle or even to sheep.
Genetically modified animals for food production are much rarer than crop plants.
An example is the genetically modified (GM) Atlantic salmon, developed in the USA
and Canada. A growth-hormone regulating gene from a Pacific Chinook salmon
and a promoter from another species of fish (an ocean pout), were injected into a
fertilised egg of an Atlantic salmon. By producing growth hormone throughout the
year, the salmon are able to grow all year, instead of just in spring and summer. As
a result, fish reach market size in about eighteen months, compared with the three
years needed by an unmodified fish. It is proposed to rear only sterile females and
to farm them in land-based tanks. The characteristics of the GM salmon reduce their
ability to compete with wild salmon in a natural environment. Below figure comparesGM salmon the big one, and farm salmon the small; both fish are 18 months.
Figure 14.7. Comparison between GM salmon and farm salmon
Application 14.4
1. Explain the meaning of transgenic organisms
2. Why is Bt maize popular with growers?
3. Discuss the process of production of pest resistant plants like Bt cotton,tomato maize corn and rice
14.5 Ethical and social implications of using genetically modifiedorganisms (GMOs).
Activity 14.5
From your daily life experience, discuss the ethical and social implications ofusing genetically modified crops in food production.
Ethics includes moral principles that control or influence a person’s behaviour.
It includes a set of standards by which a community regulates its behaviour and
decides as to which activity is legitimate and which is not. Bioethics may be viewed
as a set of standards that may be used to regulate our activities in relation to the
biological world. Biotechnology, particularly recombinant DNA technology, is usedfor exploitation of the biological world by various ways.
Some genetically modified plants are grown in strict containment of glasshouses, but
a totally different set of problems emerges when genetically engineered organisms
such as crop plants and organisms for the biological control of pests are intended
for use in the general environment. Few countries would object to the growth of
genetically modified crops that produce vaccines for human or animal use, yet there
are people who object to the growth of pro-vitamin A enhanced rice. The majorbioethical concerns pertaining to biotechnology are summarized below:
– When animals are used for production of certain pharmaceutical proteins,
they are treated as factory machines.
– Introduction of a transgene from one species into another species violates the
integrity of species.
– The transfer of human genes into animals or vice-versa is great ethic threat to
humanity.
– Biotechnology is disrespectful to living beings, and only exploits them for the
benefit of humans.
– Genetic modification of organism can have unpredictable/ undesirable effectswhen such organisms are introduced into the ecosystem.
Moreover, most objections are raised against the growth of herbicide-resistant orinsect-resistant crops as follow:
– The modified crop plants may become agricultural weeds or invade natural
habitats.
– The introduced gene may be transferred by pollen to wild relatives whose
hybrid offspring may become more invasive.
– The introduced gene may be transferred by pollen to unmodified plants
growing on a farm with organic certification.
– The modified plants may be a direct hazard to humans, domestic animals or
other beneficial animals, by being toxic or producing allergies.
– The herbicide that can now be used on the crop will leave toxic residues in the
crop.
– Genetically modified seeds are expensive, as is herbicide, and their cost may
remove any advantage of growing a resistant crop.
– Growers mostly need to buy seed each season, keeping costs high, unlike for
traditional varieties, where the grower kept seed from one crop to sow for the
next
– In parts of the world where a lot of genetically modified crops are grown, there
is a danger of losing traditional varieties with their desirable background genes
for particular localities This requires a programme of growing and harvestingtraditional varieties and setting up a seed bank to preserve them.
Application 14.5
1. Write an account on edible GM crops.
2. Discuss ethical and social implications raised against growth ofherbicide-resistant or insect-resistant crops.
End of unit assessment 14
I. Multiple choice questions
1. What is the term used for inserting a healthy copy of a gene into a person
who has a defective gene?
a. Cloning vector
b. gene therapy
c. Recombinant DNA
d. Polymerase chain reaction (PCR)
2. Which is the process used in animal cloning
a. DNA cloning
b. Recombinant DNA
c. Polymerase by nuclear transfer
3. A man and woman, each with a family history of sickle cell disease and no
children, would benefit most by:
a. Prenatal screening
b. Carrier screening.
c. Inherited predisposition screening
d. No screening because they already know their status.
4. DNA technology has many medical applications. Which of the following is
not done routinely at present?
a. Production of hormones for treating diabetes and dwarfism.
b. Production of viral Proteins for vaccines
c. Introduction of genetically engineered genes into human gametes.
d. Prenatal identification of genetic disease genes.
e. Genetic testing for carriers of harmful alleles
5. Which of the following is NOT a use of DNA profiling?
a. Determining if two DNA samples come from the same person.
b. Determining if a child could have inherited their genes from a
suspected father.
c. Determining whether a person has a given genetic disease.
d. None of the above.
II. Structured questions
6. Rearrange the statements below to produce a flow diagram showing the
steps involved in producing bacteria capable of synthesizing a human
protein such as insulin.
a. Insert the plasmid into a host bacterium.
b. Isolate mRNA for insulin.
c. Insert the DNA into a plasmid and use ligase to seal the ‘nicks’ in the
sugar phosphate chains.
d. Use DNA polymerase to clone the DNA.
e. Clone the modified bacteria and harvest the insulin.
f. Use reverse transcriptase to produce cDNA.
g. Use a restriction enzyme to cut a plasmid vector.
7. In the production of bacteria that synthesise human insulin, plasmids acted
as vectors to introduce the gene into the bacterial cells. What were the
vectors used in the production of vitamin A enhanced rice? Explain your
answer.
8. What is genetic modification (GM) of crops and how is it done? Evaluate all
possible hazards of GM crops.
9. Identify genes that have been introduced into GM crops so far and explain
its purpose.
10. Answer the following questions:
a. How does gene therapy differ from genetic screening?
b. Explain why it is easier to devise a gene therapy for a condition caused
by a recessive allele than for one caused by a dominant allele.
11. As a genetic engineer, you have a patient with symptoms that suggest a
hepatitis A infection. The symptoms come and go, but you have not been
able to detect viral proteins in the blood. Knowing that hepatitis A is an RNA
virus, what lab tests could you perform to support your diagnosis? Explain
what the result would mean.
12. Examine the figure, which shows diagrammatic DNA profiles of a mother, herchild and suspected fathers (P, Q and R) of the child.
Identify true biological father of the child. Explain your answer.
13. Some people need blood transfusions because their blood lucks important
proteins, such as those needed for blood clotting (Factor VIII). People who
receive blood transfusion have some risk of being exposed to disease-causing
viruses. How might genetic engineering eliminate this risk?
14. Bacteria and human beings are very different why is it possible sometimes
possible to combine their DNA and use a bacterium to make a human protein.
15. Describe a potential safety environmental concern with regard to genetically
modified (GM)) crops
16. The figure shows the CFTR (cystic fibrosis transmembrane conductanceregulator) protein in a cell surface membrane
a. Based on the above figure:
(i) Describe the normal function of the CFTR protein.
(ii) Use the letter E to indicate the external face of the membrane. State
how you identified this face.
b. Cystic fibrosis is caused by a recessive allele of the CFTR gene.
(i) Explain the meaning of the term recessive allele.
(ii) Explain how cystic fibrosis affects the function of the lungs.
c. As cystic fibrosis is caused by a recessive allele of a single gene, it is a good
candidate for gene therapy. Trials were undertaken, attempting to deliver
the normal allele of the CFTR gene into cells of the respiratory tract, using
viruses or liposomes as vectors. Explain how viruses deliver the allele intocells.