NATURE AND NURTURE IN BRAIN DEVELOPMENT

Nature represent the genes and it’s role while nurture represent the environment and it’s role in brain development.

The evidence for the role of nature and nurture in brain development come from a number of sources. These are;

i)The use of new born babies.

New born babies have some innate capabilities i.e innate behavior that doesn’t need to be learnt. Example s of this innate capabilities are;

a)Recognition of biological movements from non-biological movements. The babies as young as 2 years old concentrated much on biological movements e.g. that of chicken, cats , pigeons monkeys. This proved that nature is involved in brain development i.e. Biological movements are wired in the brain.

b)Abilities of young babies to distinguish human faces from others. It was proved that young babies were able to distinguish faces they see most often e.g . human faces than the faces they are not often seeing e.g. monkey faces.This indicate the role of nurture in brain development.

ii)Use of individuals with damaged brains

brains damaged by stroke or accidents have been studied and have brought new evidence. It was thought that neural connections of the cortex that control voluntary movement, speech and reasoning become fixed at a certain stage of development. Evidence now suggest that new connections may be made which bypass the damaged area with a different part of the brain taking over the job. This means that some neurons have the ability to change.

iii)The use of animals to study critical windows of development

David hubel and Torsten weisel performed a series of experiments using animals like monkeys, cats and ferrets.

2 day old kittens macaque monkeys

The most known of Hubel and weisel experiments is the use of kittens and monkeys. Their findings were as shown;

a)One lid of one eye of kittens was closed/stitched shut when the kittens were 1 week old(i.e. before their eyes had opened).The kittens could see normally with the open eye. After a period of 1-3 months the shut eye was opened and the other eye stitched shut. The observations were that the kittens were perfectly blind. There was no firing in the in the visual cortex.

b)When the lid of one eye is closed in a cat over 4 months of age which could see normally until then, it has no effect on the eye. The firing continues to occur in the visual cortex. The same procedure was done on monkeys. It is now evident that the critical period of development of visual cortex in kittens is 4-5 weeks while that of the monkeys is between 6-8 weeks.

The results of their experiments showed that there is a critical window for the development of a mature visual cortex.

The critical windows of development are the periods of time during which vital neural connections are made in the brain in response to specific stimuli. This means that if the stimuli is not received at the crucial time then the pathways will not develop normally. This shows the role of nature in brain development . However, J.C Horton and D.R. Hocking worked on infant macaque monkeys where they injected radio active tracers in the right eye 1 day after birth. They realized that the ocular dominance columns/anatomical columns were still in place/formed at the time of birth. This is through formation of particular bands on the visual cortex of the brain. Same experiment was done by Justine Crowley and Lawrence Katz on newborn ferrets. This proved the role of nature in brain development.

Ocular dominance columns in visual cortex

ocular dominance columns

iv)Use of twin studies

Identical twins share all the same genes while fraternal twins share the same number as any other sibling do.In 2007 Dr.Thad polk and his team at the university of Illinois measured the activity in the visual cortex of 24 sets of fraternal and identical twins using fMRI. The twins were presented with several sets of images which include houses, letters and people’s faces. The team then used scrambled images which could not be recognized as a base line measurement. Analysis of brain activity pattern showed the following;

a)There was more similarity in the brain activity of the identical twins than fraternal twins when they were looking at places or faces. This showed effect of nature/genetic link in brain development to respond to familiar places and faces.

b)There was little differences in brain activity patterns between fraternal and identical twins in response to words and letters. This suggested strong environmental effect/nurture and less genetic link for word and letters recognition. This makes evolutionary sense since words and letters have been with us for a very short time than people and places.

v)Cross-cultural studies

When we talk of culture we mean a system of believes shared among a group of people which shapes the behavior which is acceptable within the group. Growing in a given culture to adult hood shapes the way the brain develops. The clues and cues we use for depth perception are largely unconscious and partly learnt/environmental. For example; People from the zulu culture live in round houses and the roads are never straight. Due to this, they rarely misjudge the length of lines since they don’t live in a carpentered world full of straight lines and right angles, which are the patterns `hard wired’ in our brains as the brain develops.

vi)Studying human deprivation

Studies carried out on severely neglected children in US in 1990s where some children were left in dark cupboards with no human contact, lack of touch ,warmth, affection, language and social interactions showed very shocking revelations. The brains were very small than for average children of same age i.e. 3 years, with abnormal cortex development (cortical atrophy) amongst other abnormalities.

Normal brain Brain of depressed/severely mistreated child

How The Visual Cortex Develops during critical window.

In newborn kitten, monkey or humans , there is considerable overwrap between dendrites and synapses of the axons in the different columns in the visual cortex but in the adults there is less overwrap. Axons compete for target cells in the visual cortex. When light enters the open eye ,a nerve impulse is generated/action potential which travels along the axon and arrives at a target cell where it releases neural transmitter to the synapse which establishes it more firmly. If another neurone synapses with the same target cell, but no impulses pass along it, it don’t release neurotransmitter and eventually the synapses which are not firing are weakened and destroyed. This happens throughout the nervous system to reduce the number of unwanted axons and synapses and to make sure that messages are carried efficiently to exactly where they are needed. If one eye is shut during the critical window, no action potential arrive at synapse and therefore all the synapses from the shut eye are eliminated making the eye perfectly blind irrespective of whether rods/cones and optic nerve are working.

Investigating How The Brain Works

The great nerve tracts from the spinal cord cross over as they enter and leave the brain, so that the left-hand side of the brain receives information from and controls the right hand side of the body and vice versa. Evidences from the following studies has helped man understand how the brain functions. These are;

1.ANIMAL STUDIES

Experiments using animals like primates which are our close mammalian relatives have been done to study how the brain develops and link the same to that of humans. This is by placing an obstacle in the way of that development e.g. stitching shut one eye of a kittens and macaque monkeys during critical window of development of visual cortex.

Experiments have been done where parts of cerebral hemispheres of monkeys and dogs were removed or damaged in order to observe behavior changes in the animal and then link that change to what could happen in humans.

Other experiments involved implanting electrodes on cerebral cortex to see the effect on behavior of artificially stimulating a region of the brain.

The weakness/problem with use of animals is the human tendency to interpret animal behavior in the light of human response (anthropomorphism ). For example ,You may cage a rat and feed it well and think it is stressed or depressed yet the rat is normal and happy.

Issues About Use Of Animal In Research/Study Of How Brain Function

a)Absolutists views-Animals should not be kept or used for research. They should be accorded full animal rights e.g. right to food, water, veterinary treatment and ability to express normal behavior .

.Animal should not be used because they have ability to suffer and experience pressure just like humans.

b)Relativists views-Animals should be used for medical research so long as the benefits outweigh the harm caused.

.Animals should be used so long as harm and suffering is minimized as far as is possible.

c)It is unethical to use animals in research because animals may suffer or die in the process.

2.STUDYING HUMAN BRAIN

Human brain has been studied from conscious patients undergoing brain surgery who allow their brains to be artificially stimulated and then they describe the sensation. This shows that different parts of the brain are involved in particular functions. The patients are conscious because surgery is done under local anaesthetic because there are no sensory nerve endings in the brain.

Other information about brain function occur from situations where parts of brains are damaged or missing at birth. For example, Phineas Gage in 1848 while working as a foreman in US construction company got an accident where an iron bar passed through his head destroying most of connections between the left side frontal lobes and midbrain. This made him to lose the ability to control emotional behavior e.g. he became foul mouthed, impatient, unpleasant and irresponsible.

When the visual areas of the brain are affected severely by a disease e.g. stroke, patients show very terrible symptoms e.g. mistaking a wife for a hat! Or losing the concept of one side of the body and even the world around you e.g. eating only the left or right portion of food or applying make up only on left side of the face.

There are several medical Imaging techniques used for medical diagnosis and to investigate brain structure and function. These are;

I)Computerized Tomography (CT Scan)-This uses thousands of narrow beam x-rays rotated around the patient. Some time special dye may be injected into the blood or tissues to make the area x-ray opaque so they show more Cleary in the scan. It has the following weaknesses

a) It only captures one moment at a time and so only look at structures and damage e.g. tumor, bleeding in the brain or aneurism (swelling of arteries rather than functions . This because the images are like photographs i.e. images frozen in time .

b)It has worse resolution where small structures can’t be distinguished.

c)They use potentially harmful x-rays

Ii)Magnetic Resonance Imaging (MRI Scans)-This uses magnetic field and radio waves to make images of soft tissues like the brain. Hydrogen atoms are the commonly imaged element because they give very strong MRI signal and that most of the body is made up of water containing a lot of hydrogen atoms. Thin sections of the body are examined which give 2D image but the computer can put the sections together to form 3D images. It is used to diagnose brain injuries, stroke, tumors and infections. This can be used by doctors to link the damaged structures with patients behavior .

The weaknesses of MRI are;

a)it can’t show the brain as it works.

b)It is a very noisy procedure which is stressful.

Advantages of MRI;

a)Don’t use x-rays which can cause damage

b)Show more fine details than CT scans

c)3D image can be produced.

iii)functional magnetic resonance imaging (fMRI)

This is a modified MRI technique. It uses radio wave signal . fMRI monitors the uptake of oxygen in different areas of the brain when the brain is carrying out different tasks. Deoxyhaemoglobin absorbs the radio wave signal and latter re-emits it, while oxyhaemoglobin doesn’t absorb. When a part of brain is active blood flows to the area increasing amount of oxyhaemoglobin to the active area to supply oxygen. Less oxygen is absorbed. so an active area of the brain absorbs and emits less energy than a less active area. This can be observed in real time as different areas of the brain `light up’ on the images as they become active. This helps to study functions of various parts of the brain.

Advantages of fMRI are;

a)Shows accurate image of the brain.

b)Shows the brain as it works.

c)No damage from x-rays as it uses radio wave signals.

Weaknesses of fMRI are;

a)It is a noisy procedure hence stressful.

b)It has to be done when a person’s head remain still because movement reduces accuracy of the image.

c)some neurophysiologists argue that blood flow to an area of brain when the subject is looking at different stimuli is a case of correlation and not causation and so more research should be done to prove whether it is causal link.

Learning and memory

Learning is usually learnt through changes in behavior. Nature (genes) and nurture are involved in learning as memories are laid down.

There are two main types of behavior;

(i)Innate behavior (species characteristic behavior)

These are genetically(nature) determined responses to particular stimulus which occurs as specific neural pathways are laid down in the brain in the embryo from the instructions of the DNA. Some examples of this innate behaviors include, simple reflexes, courtship and territorial displays, suckling in young ones, crying etc unique to particular species. These types of behavior is very vital to invertebrates because they have very short lifespan hence no time to learn through trial-and –error if they are to complete their life cycles. It is also vital to both young and old vertebrates which leaves the higher areas of the brain for more complex learned behavior.

(ii)Individual-characteristic (learned behavior)

These are adapted changes in behavior of an individual which occurs as a result of experience. E.g. a child touching hot oven door learns never to touch it again. Memories are then laid down.

How do organisms learn?

a)Habituation

Habituation is part of the learning process in almost all animals. It helps the animals not to react to a repeated neutral/ harmless stimulus in their environment. Habituation may be short term or long term where response to a neutral stimulus is lost permanently. E.g. birds learn to ignore the scare crow, babies learn not to `starle’ at every sudden noise.

How is habituation to a stimulus achieved?

Repeated stimulation using harmless stimulus makes ca2+ ion channels to be less responsive . This causes less ca2+ ions to cross in to the presynaptic membrane. Few ca2+ ions means few vesicles move to presynaptic membrane to release neurotransmitter into synapse. Less neurotransmitter means less

depolarization of the postsynaptic membrane and therefore no action potential is triggered in the motor neurone . The animal can therefore not respond to the harmless stimulus and so get used to it.

b)Conditioned reflexes

In this case the animal learn to associate new stimuli with an existing unconditioned reflex e.g. The case of Pavlov’s dogs associated the sound of the bell with food hence could salivate every time they heard the sound of the bell.

c)Trial -and –error (operant learning)

if a trial behavior is rewarded e.g. with food the behavior is repeated or if the animal is punished e.g. the animal is hurt such behavior is never repeated. Memories are then laid down.

d)Imprinting

This is simple and specialized sort of learning which occurs to young animals where they identify with another animal(usually the mother) or if parent is not available then another large object or animal.It will then follow this object and relate to other similar objects throughout life.

e)Exploratory (latent) Learning

this takes place when an animal explores new surroundings and learns them without immediate reward or punishment. The information may then be useful at another time.

f)Insight learning

This is based on thought and reasoning as seen in mammals especially primates. It is regarded as the highest sort of learning. Once the problem is solved, the solution is then remembered next time such a similar/related problem arises.

BRAINS, THE GENOME AND MEDICINE

Communications between your neurons both around the body and in the brain largely depends on naturally occurring chemicals called neurotransmitters. Examples of neurotransmitters are acetylcholine, dopamine, serotonin, noradrenaline and adrenaline. Some neurotransmitters are only found in the brain synapses e.g. serotonin and dopamine and their imbalance can cause severe mental and physical symptoms. To treat such diseases means getting the drugs across the blood -brain barrier

Which is formed by the endothelial cells which line the blood capillaries of the brain which are very tightly joined together. This is difficult to deliver the drug but good because it prevents the bacteria getting into the brain to cause infections. Drugs that affect the brain are only active at the synapses and there are a number of stages during synaptic transmission when they are supposed to be targeted.

DIAGRAM 1 DIAGRAM 2

The seven stages of synaptic transmission shown in diagram 2 can all be affected by drugs which may cure a problem or cause one.

1.PARKINSON’S DISEASE

This is a brain disease which involves loss/death of dopamine producing nerve cells in an area of the midbrain called substantia nigra. The axons from these nerve cells spread through frontal cortex, the brain stem and the spinal cord and therefore they are closely involved in control and coordination of movement. The death of these cells result to loss of motor control. However parkinson’s disease occur mostly to people of over 50 years old and symptoms arise when most of 80% of dopamine producing cells are lost.The cause of parkinson’s disease is not known but rarely is genetical while some environmental factors such as toxins, herbicides and pesticides are linked to parkinson’s disease.

Some of the symptoms of the disease are;

a) Tremor starts in one hand for 70% of the people.

b) Slowness of movement i.e. hard to get started .

c) Rigid muscles which make it difficult to get up after sitting on a chair or to turn in bed.

d)Poor balance.

e)Problems in sleeping, depression, and difficulties in speech and breathing.

Treating the symptoms of parkinson’s disease;

Use of drugs to increase dopamine level or allow the body to use the available dopamine well are used. Examples;

a)Levodopa (L-dopa)-L-dopa is a precursor of dopamine which is used because it can cross the blood brain barrier unlike dopamine. L-dopa allows the remaining cells to continue producing as much dopamine as possible .However it becomes less effective as more cells continues to dieoff.

b)Dopamine agonists-These are chemicals which mimic the effect of dopamine by binding to dopamine receptors for action potential/nerve impulse to be generated. They are usually used at the beginning of the disease when they are very effective saving on L-dopa for later stages of diseases.

c)MAOB inhibitors-monoaminoxidase B inhibitors prevent the breakdown of the little dopamine produced in the synapse by the MOAB enzyme.

d)Gene therapy –This is still an area of research aimed at inserting a healthy allele/gene to dopamine producing cells in order to prevent death of these cells or increase dopamine production in remaining cells. The problem will be safe delivery of the healthy gene to the cells of midbrain.

e)Stem cell therapy-Embryonic stem cells can be implanted in the brain to replace the dead dopamine producing cells. The problems in this area of research are;

i) Risk of cancer developing due to uncontrolled cell division/growth.

ii)The trigger to make embryonic stem cells to become dopamine producing cells is still being researched on/not yet known.

2.NEUROTRANSMITTERS AND DEPRESSION

Depression is a serious illness whose causes are complex and not fully understood. However the following may be causes of depression;

a)Problems with neurotransmitter serotonin-serotonin is a neurotransmitter which is produced by nerve cells in the brain stem which have axons which spread throughout the brain into the cortex, the cerebellum and the spinal cord. This means they have widespread effect hence low level of serotonin means few nerve impulses move around the brain so overall brain activity is suppressed. This causes depression. In fact abnormal serotonin pathways are found in people with depression.

b)Dopamine and noradrenalin imbalances-These are also involved in causing depression in some people.

c)External factors such as bereavement, work or relationship stress.

d)Genetics causes of depression-scientists have discovered a gene (5-HTT) which appear to be linked to serotonin production in the brain. The gene codes for a reuptake protein which enable serotonin to be taken back into the presynaptic membrane after release in to the synapse.

The gene exists in three forms-short form(homozygous), Long form (homozygous) and long/short form(heterozygous).It has shown that in all forms of the gene, the reuptake protein is synthesized but more amount is formed in those with long form, moderate amount in heterozygotes but very little in short form. This therefore means highest risk of depression in short form, moderate in heterozygotes and minimal risks in those with long form of the gene if there is an adverse life event like bereavement.

TREATING DEPRESSION

i)Talking therapies-This helps the patient to come to terms with adverse life events like bereavement .

ii)Use of antidepressant drugs e.g.

(a)selective serotonin reuptake inhibitors ( SSRIs)- These drugs inhibit reuptake proteins from taking serotonin back to presynaptic membrane such that more serotonin remain in the synaptic cleft and so more impulses pass to post-synaptic axon. This helps to lift the mood and improves ability to sleep.

(b)Tricyclic antidepressants (TCAs)- these work by increasing the level of serotonin and noradrenalin production in the brain which boosts moods.

iii)MOAB inhibitors-These prevent breakdown of monoamines in the synapse by MAOB enzymes reducing some forms of depressions.

DRUGS AND THE BRAIN

Therapeutic and Legal drugs such as L-dopa and SSRIs have great effects on how the brain works.

Enjoyable and legal drugs such as caffeine from coffee and tea also has an effect in the brain.

Caffeine crosses the blood brain barrier. In the synapse caffeine slow down the rate of re-absorption of dopamine from the synapse which allows more impulses to close postsynaptic neurons serving as a stimulus by increasing blood pressure.

Illegal Drugs e.g. Ecstasy (MDMA or 3,4-methylenedioxy-N-methylamphentamine).

Ecstasy acts as a stimulant increasing heart rate like amphetamine. It acts also as a psychotropic drug which alters the way a person sees the world. It changes mood making people feel happy, sociable, warm and empathetic. This is because the drug blocks the serotonin reuptake system so that serotonin floods the synapse and can’t get back to pre-synaptic knob hence the brain if flooded with synapses. It is also believed that the high level of serotonin as a result of ecstasy drug stimulates production of more dopamine.

Problems with ecstasy use include;

a)causes increased heart rate hence a risk in CVDs.

b)Stimulates over-production of Antidiuretic hormone (ADH).This prevent the kidney from excreting excess water. Cells then absorb water by osmosis and bursts which can cause death.

c)The person don’t feel thirsty and therefore this can lead to overheating(hyperthermia) which result to high blood pressure, irregular heart beat and enzyme/protein denaturation which can cause death.

PHARMACOGENOMICS

The human genome project was set up to identify all the genes present in the human chromosomes and to sequence the 3 billion base pairs which make up the human DNA and make the results available to all the scientists across the globe.

The Human Genome project demonstrated that every individual has at least 99.9% of their DNA in the common. Other 1000 DNA projects have been set up so that they can provide as much information about the biomedically relevant variations from at least 1000 people and the information made available to all scientists across the globe. Each individual –apart from identical twins-is genetically unique. The results o f DNA analysis from Human Genome Project will help the pharmacogenomics to develop efficient drugs as genetic factors have a marked effect on the efficiency of some drugs.

Pharmacogenomics is a new branch of science which has been developed to link pharmaceutical expertise with the knowledge of human genome.

The Expected Impact Of Human Genome Project In Drug Industry/potential benefits of pharmacogenomics.

The following are the expected benefits from the Human Genome Project /pharmacogenomics ;

i)Knowing the person genome will help the doctor to prescribe the right drug which will not give adverse drug reactions.

ii)Most adverse drug reactions results to either death, permanent damage to organs like the liver, kidneys and also lost earnings and quality of life. This is a great loss economically which will be saved if drugs are tailor made to fit specific people who have a problem with certain drugs.

iii)genetic information of a person will help doctors to understand how rapid a patient’s body will respond to and excrete a particular drug. This will ensure the right dose is given to the patient. Currently

drug dosage is given depending on body weight or age which is very tricky as overdose or underdose may occur.

Cytochrome P450 gene codes for certain liver enzymes which are involved in many drugs breakdown/detoxification. Knowing a person’s genome will therefore help in administering the right dosage as people with the variant of P450 gene either have less active or even inactive enzymes hence are at risk of a drug overdose.

iv)Knowing the fine details of human genome will make it easier to develop drugs which only targets the pathogen or cancer cells without damaging the healthy cells.

v)Finding genetic targets for particular diseases could make it possible to isolate a suitable drug candidate more rapidly. This will also make it possible to treat more diseases and treat them more effectively.

vi)Knowing ones genome makes one understand the diseases one is at risk from. This will help you to prepare on how to prevent yourself getting the disease if it is possible to do so.

Issues With The New Science Of Pharmacogenomics

(i)Economical issues.

a)Identifying genes which affect the response to a particular drug is difficult, time consuming and very expensive. Is the potential benefit worth the financial investment society needs to make?

b)Is it worth to spend more money on five drugs meant to cure only 25% of population who experience adverse drug reaction or to produce one drug `one size fits all’ which will be used by all or 75%.

(ii)Ethical &moral issues

a)It is in order to tell people that a particular drug won’t work for them. But is it ethical to leave people with particular genetic variation with no treatment available?

b)Is it moral or ethical to give a drug to a group of patients knowing it won’t work for them or will give adverse reactions.

c) Yes ,it will be a big financial implication to the society in training doctors and pharmacists to recognize all possible drugs permutations and keeping them up to date. But it will be grossly unethical not to go ahead with the training.

d)Will it be ethical to have a pharmacogenomics DNA data base for every person only for it to be used in fighting crime or overcoming immigration issues?

(iii)social issues

a)Who will pay for the development of the new therapies and drugs?

b)Will every patient be able to afford the high cost drugs designed for his genome only?

c)Who is entitled to know the information about your genome if it is sequenced?-Insurance companies, police (forensic investigators incase of crime),Doctors, family members e.t.c ?

THE USE OF GENETICALLY MODIFIED ORGANISMS (GMOS)TO PRODUCE DRUGS

Drugs can be produced from the following organisms which can be genetically modified through inserting a gene from human which codes for human proteins .This is by use of a vector to insert the gene to the target cell.

(i)Use Of Genetically Modified Microorganisms To Produce Human Insulin

Procedure 1

Since insulin hormone is made up of two polypeptide chains coded for by different genes, then 2 genes each for one chain must be used.

Extract an insulin secreting cell and remove DNA from it.

Cut the insulin gene out of DNA using restriction endonuclease enzymes.

Extract 2 plasmids from 2 bacteria.

Cut open the 2 plasmids using the same restriction endonuclease enzymes.

Use DNA ligase enzymes to splice (join together) the 2 different Insulin genes, special marker genes and the cut plasmids .This forms recombinant plasmids. The plasmid serves as a vector to insert the gene into the bacteria. Special marker genes are either antibiotic resistant genes which allows for identification of the bacteria with the insulin gene.

Incubate the recombinant plasmids with bacteria which have their plasmids removed. Some bacteria take in recombinant plasmids and are easily identified as they have the special marker gene. The bacteria are now transgenic bacteria.

Culture the 2 transgenic bacteria in different industrial fermenters to produce insulin polypeptide chains.

Pass the mixture from the fermenter to downstream processing to obtain 2 pure polypeptide chains.

The two chains are then oxidized to join them together via disulphide bond to form pure human insulin (Humulin ) which functions exactly like human insulin.

Procedure 2

A synthetic gene which now mimics the human gene for insulin is cut of synthetic DNA using restriction endonuclease.

Extract a plasmid from a bacteria.

Cut open the plasmid using the restriction endonuclease enzymes.

Use DNA ligase enzymes to splice (join together) the synthetic Insulin gene, special marker genes and the cut plasmids .This forms recombinant plasmids. The plasmid serves as a vector to insert the gene into the bacteria. Special marker genes are either antibiotic resistant genes which allows for identification of the bacteria with the insulin gene.

Incubate the recombinant plasmids with bacteria which have their plasmids removed. Some bacteria take in recombinant plasmids and are easily identified as they have the special marker gene. The bacteria are now transgenic bacteria.

Culture the transgenic bacteria in different industrial fermenters to produce Proinsulin

Pass the mixture from the fermenter to downstream processing to obtain pure proinsulin.

Use enzymes to convert proinsulin to insulin (humulin).

(ii)Making transgenic plants to produce drugs e.g. Hepatitis B vaccines

Step 1 Step 2

Internet GM plant cell Bacteria A.tumefaciens insert desired gene

Agrobacterium tumefaciens causes tumors in plants which are called crown galls.The bacteria contain a plasmid called Ti plasmid which help the bacteria to introduce bacterial DNA directly into plant DNA. It is this bacterial DNA which causes crown gall (tumour) in plants. Modified A.tumefaciens Ti plasmids are now used as a vectors of the desired gene e.g. human gene for hepatitis B to plant cells .

ProcedureHuman gene which produce antibodies against Hepatitis B is cut off the human DNA extracted from the cell using restriction endonuclease enzymes.A modified A.tumefaciens Ti plasmid is opened using restriction endonuclease enzymes.The desired gene together with marker genes and promoter DNA are spliced/ joined to the Ti plasmid to form recombinant plasmid. The recombinant Ti plasmid is then placed back to the bacteria which is incubated together with plant cells.The plant cells can then be cultured in callus initiation medium and then in growth medium to give GM identical plants which canbe grown in the field to produce hepatitis B vaccines.

NB:-Marker genes are used for identification of GM plant. It may also contain alleles which make the plant infertile to ensure safety of environment(safety of wild species).The promoter DNA ensures the expression of the new gene occurs.

The vaccines has the following advantages;a) Will be available locally to people-poor farming communitiesb) Will be cheapc) Don’t need to be cool storage facilities. d) Don’t need qualified health to administer vaccines against these deadly

diseases

S

(iii)Making transgenic animals e.g. goats to produce drugs/ human proteins.

New traits can be introduced into animals. Here's how it works for animals

engineered to produce a human pharmaceutical.

Procedure;

1. A copy of human gene which codes for the required human protein e.g.

alpha 1-antitrypsin is cut off the human DNA using restriction

endonuclease.

2.The gene is then spliced/joined together with the following ;

A. Milk Protein Promoter DNA: allows for expression only in goat mammary

glands.

.

b. Terminator Sequence: assures that only the gene of interest is controlled

by the milk promoter DNA.

c. Other DNA Sequences: helps with the introduction of the new

combination DNA strand into the egg nucleus.

NB:- the resulting DNA is called DNA construct.

3. This new DNA strand is then introduced by any of a number of the

following methods into an egg cell removed from a goat ;

a)liposomes-DNA wrapped in liposomes which fuse with egg cell membrane

to get DNA into cell cytoplasm.

b)Harmless virus.

c)Microprojectiles-This includes Shooting DNA at very high speed to a goat

eggs using minute gold or tungsten pellets. Some egg cells accept the DNA.

d)Use of micropipettes to inject DNA to many egg cells till some get the

DNA.A micromanipulator is used to avoid trembling of hands which can

damage egg cells.

4.The egg containing the accepted DNA is then fertilized (invitro) to form an

embryo.

5.The embryos are then implanted into the uterus of other goats /surrogate

mothers and a genetically engineered animals/goats is born.

6. The offspring of the first genetically engineered goats, referred to as

production animals, are tested for the transgenic gene.

7.Those with the transgenic genes(F1 generation offsprings) are called

founders and the females are used as the production herd.

8. The milk produced is transferred to a purification facility where the drug

to be used to treat human disease is purified from the goat's milk.

Examples of drugs produced are;

Alpha-1-antitrypsin(AAT)-treats people with a genetic condition which

affect liver and lungs causing early emphysema.

Factor v11 and 1x - components of clotting cascade absent in

haemophiliacs

Activated protein c-treats deep vein thrombosis.

Issues associated with use of Genetically Modified Organisms

(GMOs)

(i)Genetic pollution (Transfer of the genes to natural ,wild species) through

cross pollination.

(ii)Antibiotic resistant gene is used to identify GM bacteria which could lead

to antibiotic resistance developing in other bacteria.

(iii)GM crops could become super –weeds that out compete other plants and

may be resistant to herbicides.They could damage natural food chains,

resulting in damage to the environment because they would encourage

farmers to use more selective herbicides to kill everything but the crops.

(iv)GM crops may not produce fertile offsprings/seeds.This prevent farmers

collecting seeds and replanting, so they need to return to the biotechnology

company to buy new seeds for each planting.This could make them too

expensive for some farmers.

Ethical issues of using GMOs

(i)Genetic modification violates the rights of animal modified.

(ii)The technology will just be property of a few companies in richer

countries only.