Application of reproduction and genetics

Question 1

What is embryo cloning?

Answer 1

This technique has been used to produce genetically identical individuals amd has made it possible for farmers to increase the numbers of their animals. Eggs are taken from high milk yielding cows and are fertilised in a Petri dish using sperm from the best bulls. This is know as in vitro fertilisation. The fertilised egg divides to form a ball of cells. This group of cells or young embryos is split into separate cells. Each of these cells will then develop into a new embryo, genetically identical (clone) to the original. The embryos are then transplanted into other cows called surrogates.

Question 2

What happens in nuclear transfer?

Answer 2

1) cells are taken from the tissues of the udder of a sheep (donor) and cultured in a medium which stops division
2) An unfertilised egg is removed from a different sheep (the recipient) and the nucleus is removed, leaving an egg cell without a nucleus
3) The donor and recipient cells are fused together using a gentle electric pulse, and allowed to divide to the eight cell stage producing a ball of cells.
4) The developing embryo is implanted into the uterus of another sheep (the host or surrogate)
5) The lamb is genetically identical to the original sheep.

Question 3

What are the advantages of nuclear transfer?

Answer 3

1) Cell culture is useful for production of cells in quantity e.g. cancer cells for medical research, monoclonal antibodies
2) The production of a single, identical, genetic line of cells with desirable characteristics may be used to maintain genetic stocks
3) Endangered animals unable to have offspring can however reproduce by cloning.

Question 4

What are the disadvantages nuclear transfer?

Answer 4

1) In mammals the technique is very expensive and unreliable
2) There may be the inadvertent selection of disadvantageous alleles
3) The genetic age of the clone is the same as the original parent and the clone develops age related conditions early in life.
4) Genetic uniformity in an endangered species makes it less likely to be able to cope with or adapt to changes in the environment.

Question 5

What is tissue culture?

Answer 5

The technique of growing cells in a lab

Question 6

What does tissue culturing involve?

Answer 6

Inducing living cells to grow on a framework of synthetic material to produce a tissue such as skin tissue (treatment if extensive deep burns). Blood vessel replacement, bone and cartilage care and treatment of degenerative nerve disease and stem cells.

Question 7

What are stem cells?

Answer 7

An undifferentiated cell capable of dividing to give rise to cells which can develop into different types of specialised cells.

Question 8

Where can stem cells be found?

Answer 8

In adult animal tissues and selective tissue called bone marrow. Found in earliest stage of embryo development before cells have differentiated (embryonic stem cells)

Question 9

What are stem cells used for?

Answer 9

1) To generate organs for transplantation- prevent immune rejection and organ shortage
2) Treat variety of genetic disorders e.g. Parkinson’s, alzheimers, heart disease, liver disease and diabetes.

Question 10

What are the ethical issues?

Answer 10

1) It can devalue human life- Playing god - creating life then destroying it
2) Destroys embryos when removing stem cells
3) Problems obtaining consent from parents after IVF
4) Can turn into tumours

Question 11

What technique is used to grow stem cells?

Answer 11

1) A mature cell is taken from the patient and the nucleus is removed
2) The nucleus is removed from a human ovum
3) The mature cell nucleus is transferred into the ‘empty’ ovum
4) The ovum, containing the patient’s DNA, divides to form a ball of stem cells
5) Stem cells are isolated and cultured with appropriate growth factors, allowing them to grow into the required organ or tissue

Question 12

What is Micropropagation?

Answer 12

It involves the cloning of plants. It is based on the ability of differentiated plant cells to give rise to all the different cells of the adult plants (totipotent - cells that can mature into any body cells)

Question 13

What are meristems?

Answer 13

Growing points where cells divide rapidly by mitosis at tips of roots and shoots.

Question 14

How are genetically identical plants developed?

Answer 14

Cells are removed from meristem and placed in suitable conditions.

Question 15

What steps are followed in micropropagation?

Answer 15

1) A plant with the desired characteristics is selected
2) A sterile scalpel is used to remove the meristem from the shoot
3) The meristem is cut into small pieces called explants
4) The explants are placed onto a sterile aerated nutrient medium such as agar jelly
5) The cells are allowed to divide by mitosis producing a mass of undifferentiated cells, called callus
6) The callus is subdivided and each piece is allowed to differentiate into a plantlet
7) When they have reached a suitable size the plantlets are transplanted into sterile soil.

Question 16

What are the advantages of plant tissue culture?

Answer 16

1) Large numbers of plants can be grown in sterile controlled conditions ensuring a greater survival rate than would be the case if seeds were planted outside
2) It is less time-consuming as it cuts out the requirement for pollination, seed production and seasonal restrictions on germination
3) Good quality stock is selected, possessing qualities such as resistance to disease or high yield. By this means plant diseases can be eliminated.
4) The crop is uniform since the plants are genetically identical. From a commercial viewpoint this is very important.
5) Large numbers of plants can be stored in a small area with reduced heating and lighting costs
6) Unique genotypes can be preserved
7) Reduced space is required for transport

Question 17

What are the disadvantages of plant tissue culture?

Answer 17

1) Sterile conditions have to be maintained, otherwise bacterial or fungal contamination of the culture medium may result with subsequent loss of plants
2) The plants are genetically unstable with an increased rate of mutation in medium-grown cells leading to abnormality in the plantlets. Regular inspection is needed to remove any defective individuals, thus labour costs are higher than with traditional propagation methods.

Question 18

What were the main aims of the Human Genome Project?

Answer 18

1) Identify all the approximately 20,000-25,000 genes in human DNA
2) Determine the sequences of the 3 billion chemical base pairs that make up human DNA
3) Store this information in database
4) Improve tools for data analysis
5) Transfer related technologies to private sector
6) Address the ethical, legal and social issues that may arise from project

Question 19

What does the information enable scientists to do and how?

Answer 19

To know exactly which sections of DNA on which chromosomes are responsible for the many different inherited diseases. It takes place by:

1) A DNA sample is obtained from a patient and scanned for mutated sequence
2) Gene probes are used to seek their complement among the three billion base pairs of human genome
3) If the mutated sequence is present, the probe will bind to it and flag the mutation

Question 20

What are the main uses of genetic testing?

Answer 20

1) Carrier screening which involves identifying unaffected individuals who carry one copy of a gene (recessive) for a disease that requires two copies for the disease to be expressed such as cystic fibrosis. People who are carriers can then decide whether they would like children or antenatal genetic test to check whether the child will be born with this disease.
2) Pre-implantation genetic diagnosis
3) Pre-natal diagnostic testing
4) New-born baby screening
5) Pre-symptomatic testing for predicting adult-onset disorders such as Huntington’s disease
6) Pre-symptomatic testing for estimating the risk of developing adult-onset cancers and Alzheimer’s disease
7) Confirmation that an individual has a suspected disease
8) Forensic/identity testing

Question 21

what can genetic testing do?

Answer 21

It can give an idea od the probability of developing a particular disease. Those people at greater risk can be targeted by health authorities, screened at particular intervals and given appropriate advice into how to reduce the risk by changing lifestyle. Once the base sequence is know it is possible to find out the protein that it codes for and once the structure of the protein is know it is possible to design drugs who’s molecules would fit it perfectly.

Question 22

What are the advantages of gene testing?

Answer 22

1) Dramatically improves lives - clarify diagnosis and direct a physicia toward appropriate treatment. Advice families to avoid having children with devastating illnesses or identify people at high risk of acquiring a disease to help prevent them
2) Give probability of getting a disease

Question 23

What are the disadvantages if gene testing?

Answer 23

1) Difficulty of interpreting positive result as some people who carry a disease- associated mutation never develop the disease. This is believed to be the case as mutations may work together with other unknown mutations or environmental influences to cause disease
2) Possibility of laboratory error- sample misinterpretation, contamination of chemicals used for testing or other factors
3) Current lack of available medical options for these disease
4) Tests potential of creating anxiety, discrimination and social stigmatisation.

Question 24

What are the social concerns of gene testing?

Answer 24

1) Who should have access to personal genetic information and how will it be used?
2) Who owns and controls the genetic information?
3) Should parents have the right to have their children tested for adult-onset diseases?
4) Is there a danger of one day producing human clones?

Question 25

What is cystic fibrosis due to?

Answer 25

A defective autosomal recessive allele.

Question 26

What are effects of cystic fibrosis?

Answer 26

Sufferers produce a thick, sticky mucus from the epithelial cells linin certain passageways in the body.

Question 27

What do the secretions from cystic fibrosis lead to?

Answer 27

1) The pancreatic duct becomes blocked, preventing pancreatic enzymes from reaching the duodenum and so food digestion is incomplete
2) The bronchioles and alveoli of the lungs become clogged, causing congestion and difficulty in breathing. The mucus is difficult to remove and leads to recurrent infections.

Question 28

How is distress and breathing relieved when got cystic fibrosis?

Answer 28

Frequent daily physiotherapy massage is needed to keep airways open. The sufferer also has impaired digested and a limited absorption of food.

Question 29

How does some inherit cystic fibrosis?

Answer 29

Both parents must be carriers of the defective recessive allele. The normal gene codes for the production of a protein found in the cell membrane (cystic fibrosis trans-membrane regulator) which transports chloride ions out of cells into mucus. Sodium ions follow out of the cells and water passes out of the cell by osmosis. This makes the mucus that lines the air passages a watery consistency. The protein of cystic fibrosis sufferers lacks just one amino acid and so cannot perform its transport function.

Question 30

How have microbiologists succeeded in isolating and cloning the gene which codes for the CFTR gene?

Answer 30

1) Using liposomes:
- The genes are inserted into liposomes which involves wrapping the gene in lipid molecules that can pass through the membranes of lung epithelial cells
- An aerosol inhaler is used to add the no-defective gene to the epithelial cells of the lung
- The liposomes fuse with the phospholipid bilayer of the cell membrane and the DNA enters the cells. These cells start to express the inserted gene by making the protein CFTR
2) Using a Virus:
- The virus is rendered harmless
- The virus is cultured in epithelial cells along with plasmids with the normal CFTR gene inserted
- The gene becomes incorporated into the virus DNA
- The gene becomes incorporated into the virus DNA
- The virus is isolated and introduced into the patient by means of an inhaler
- The virus injects the plasmid DNA which includes the normal CFTR gene, into the epithelial cells of the lungs

Question 31

How effective is gene therapy?

Answer 31

Limited success- effect is short lived and may need to be repeated in 30 day intervals. Only a small proportion of the genes are expressed and may be an immune response in the patient. To give a child that would be born with genetic disease the chance of a normal life, or to prevent the development of cancer in an individual is main advantage.

Question 32

What are the uses of genetic counselling?

Answer 32

Advice may be given on:
1) Whether there is a history of the disorder in the family
2) Whether the parent are closely related
3) The frequency of the faulty gene in the general population
This enables people to make personal decisions about themselves or their offspring

Question 33

What techniques can investigate whether a child is affected before born?

Answer 33

1) A simple blood test for detecting cystic fibrosis
2) Amniocentesis - involves withdrawing some of the amniotic fluid at 15-20 weeks i.e. about halfway through pregnancy. The fluid contains cells that have floated away from the surface of the embryo. These cells may be analysed microscopically
3) Chorionic villus sampling - Early In pregnancy (8-10 weeks) tiny samples of foetal tissues are withdrawn from the uterus and cells are cultured and examined under the microscope.

Question 34

What are the advantages of gene therapy?

Answer 34

Couples may find that they are carriers of genetic diseases and then can decide if they want to have a child that could be born with a defect

Question 35

What are the disadvantages of gene therapy?

Answer 35

1) Many believe it is an invasion of privacy
2) Some believe if prenatal tests are carried out more abortions will take place
3) Individuals with defects may be placed in high risk of insurance purposes to cover treatment so could be very expensive or difficult to obtain
4) Many fear that companies will use gene therapy for wrong reasons such as choosing or modifying the characteristics of a child

Question 36

What does genetic engineering allow?

Answer 36

Genes to be manipulated, altered and transferred from one organism to another.

Question 37

What doe the applications of genetic engineering include?

Answer 37

1) Transfer of genes into bacteria so that they can make useful products such as insulin
2) Transfer of genes into plants and animals so that they acquire new characteristics e.g. resistance to disease
3) Transfer of genes into humans so that they no longer suffer from a genetic diseases such as cystic fibrosis

Question 38

What is the process of producing a protein using gene transfer and cloning?

Answer 38

1) Isolation of the DNA fragments
2) Insertion of the DNA fragment into a vector
3) The transfer of DNA into suitable host cells
4) Identification of the host cells that have taken up the gene by use of gene markers
5) Cloning of the host cells.

Question 39

What are the 2 methods of isolation used?

Answer 39

Restriction endonuclease or reverse transcriptase

Question 40

What happens during restriction endonuclease?

Answer 40

The gene is isolated from the rest of the DNA in a human cell. An enzyme is called restriction endonuclease is used to cut the DNA into small pieces allowing individual genes to be isolated. The enzyme cuts DNA between specific base sequences which the enzyme recognises. most restriction enzymes make a staggered cut in the DNA double helix. The unpaired bases at the cut form sticky ends. They are a palindrome - GAATTC

Question 41

What happens in reverse transcriptase?

Answer 41

1) The mRNA can be extracted
2) The addition of an enzyme (reverse transcriptase) made by a group of viruses called retroviruses is used to make a DNA copy of mRNA. This single strand of DNA is called copy DNA or cDNA. Many copies of cDNA are made
3) The addition of DNA polymerase converts this to a double strand for insertion into a plasmid.

Question 42

What happens when inserting the gene into a vector?

Answer 42

The vector is a plasmid (small circular piece of DNA found in bacteria). To obtain the plasmids the bacteria containing them are treated to dissolve their cell walls and the plasmids are separated using the same enzymes, restriction endonuclease. The enzyme makes staggered cuts (sticky ends) which allow the donor DNA to be spliced into the vector DNA. this takes place when the donor and vector DNA are mixed together. The sticky ends are complementary and the C and G bases on their sticky ends pair up. Another group of enzymes called DNA ligase are used to join the donor and vector DNA together.

Question 43

How is DNA transferred into host cell and how are genetic markers used?

Answer 43

The recombinant DNA needs to be transferred into bacterial cells. This involves mixing the plasmids and bacteria together in a medium containing calcium ions allowing the plasmids to pass into the bacteria. However, only a small proportion (1%) of bacterial cells take up the plasmids so it’s therefore necessary to identify which bacterial cells have taken up the plasmid involving the use of antibiotic resistant genes. The low take-up may be explained as some plasmids close up without incorporating the DNA fragment. All the bacterial cells are grown on a medium that contains the antibiotic, ampicillin. Bacterial cells that have taken up the plasmids will have acquired the gene for ampicillin resistance. These bacterial cells are able to break down the antibiotic and survive. Using the bacteria that have taken up a piece of foreign DNA successfully, the foreign DNA replicates along with the rest of the plasmid every time the bacterial cell divides. Cloning of the recombinant containing bacteria, results in the production of multiple copies of the recombinant gene, That is the bacteria divide repeatedly and give rise to a large population of bacterial cells all of which contain replicas of the foreign DNA. The genetically modified bacteria are cultured on a large scale using a fermenter and produce insulin which is extracted and purified.

Question 44

What is a marker gene?

Answer 44

Some plasmids carry a gene for antibiotic resistance and this is unaffected by the introduction of the new gene.

Question 45

What are genetically modified crops?

Answer 45

Bacteria are readily introduced into plants. Certain species naturally attack damaged plants and cause the plant cells to multiply and form a tumour. The bacteria do this by inserting genes from their own plasmids into one of the plant’s chromosomes. The plasmid gene links with the DNA of the plant but stimulates the growth of a tumour. Scientists can replace the tumour-forming genes in the bacterial plasmids with useful genes.

Question 46

What are examples of transgenic or GM crops?

Answer 46

1) Soya beans - very important as source of food used in flour, protein and oil so used in bread, biscuits, baby foods, soya milk. Certain varieties of soya plants have been modified to be tolerant to week killer. This allows the weed-killer to be sprayed onto the crop without affecting it but it kills all the weeds. The weed killer breaks down in the soil into harmless components.
2) Tomatoes - ripen naturally as produce enzyme which breaks down the pectin in their cell walls. Scientists have developed a genetically modified tomato called “FlavrSavr”. A gene has been introduced into the tomato plant having a base sequence complementary to that of the gene producing the enzyme. The mRNA transcribed from the inserted gene is therefore complementary to the mRNA strand of the original gene. The two combine to form a double strand, This prevents the mRNA of the original gene from being translated and effectively blocks the production of the enzyme. This result is that FlavrSavr tomatoes have a longer shelf life and taste so hard when arrive at stores.

Question 47

Why are people opposed to GM crops?

Answer 47

1) Concerns that GM plants through pollination will transfer their genes to wild relatives or similar crops growing nearby with unforeseen effects e.g. plants with introduced genes that enable them to be resistant to insect attack will lead to a population of resistant insect pests.
2) GM crops contain marker genes. Some marker genes confer antibiotic resistance. There is a concern that some of these genes may be transferred to the bacteria in the intestine of the consumer
3) Plant breeding may fall into the hands of a few commercial companies which means fewer varieties will be offered to farmers making crops more susceptible to attack by pests and diseases and lead to a reduction in the use of important old varieties of wild varieties.
4) If GM crops are to be grown commercially in the UK organic farm produce will be compromised. Pollen from GM crops, spread on the wind and by insects could find its way to organic fields and beehives.

Question 48

What are the advantages of GM crops?

Answer 48

1) Solving food shortages in various parts of the world perhaps also enabling crops to be grown in drought areas
2) Producing improved food with improved flavour and better keeping qualities
3) Reducing the harmful effects of modern farming by introducing nitrogen-fixing genes into crops such as rice and wheat reducing the use of artificial fertilisers
4) Introducing genes that confer resistance to insects, weeds and insects.

Question 49

What is genetic fingerprinting?

Answer 49

A person’s DNA profile:

1) The DNA is extracted from the sample and cut into small fragments using restriction endonucleases
2) The DNA fragments are separated by a technique know as electrophoresis. Since the fragments are negatively charged they move towards the positive terminal. The smaller the fragment the faster it moves and the DNA becomes separated into bands according to the size of the fragments
3) The trough is covered with a nylon membrane and the fragments are transferred to the membrane by a process called Southern blotting
4) Radioactive DNA probes (now largely replaced by non-radioactive or chemiluminescent probes) are used to attach to specific parts of the fragments and any unboung fragments are washed off
5) The nylon membrane with DNA fragments attached is placed under X-ray film and the radioactive probes expose the film
6) This autoradiograph reveals a pattern of light and dark bands (the dark band indicates where a radioactive probe is present) which are unique to individuals and is called a genetic fingerprint

Question 50

Where are the band in a fingerprint inherited from?

Answer 50

Inherited from both parents which can be used in paternity suits and can also be used to convict criminals. To do this white blood cells are taken from the mother and the possible father. The bands of the mother are subtracted from the child’s pattern. If the man is the true father, he must possess all the remaining bands in the child’s genetic fingerprint.

Question 51

What is polymerase chain reactions?

Answer 51

Semi-conservative replication of DNA in a test-tube.

Question 52

What are the stages of polymerase chain reactions?

Answer 52

1) The original DNA (target DNA) is heated to 95c and it separates into two single strands
2) The solution is cooled to 55c triggering the primers to join to the complementary base sequence on each of the single strands of DNA. This is turn triggers DNA replication
3) The solution is heated to 70c and DNA polymerase (which is not denatured at the temperature) catalyses the synthesis of a complementary strand for each of the single strands of DNA, producing two identical double strands of DNA
4) Steps 1-3 are repeated many times, doubling the quantity of DNA produced each time

Question 53

What are the issues of privacy associated genetic fingerprinting?

Answer 53

This genetic fingerprinting information is used for phylogenic studies, forensic science, paternity studies etc. This raises concerns regarding the storage of the information as well as who has access to the data. Will insurance companies use the data to determine life and health insurance premiums? Also efforts are being made to store genetic material from many races and tribes before isolated tribes are intermixed and lost. This is scientifically useful nut careful ethical standards need to be maintained in order that genetic privacy is maintained and that no misuse of the information occurs in the future.

Question 54

What are the advantages if genetic engineering?

Answer 54

1) The large-scale production of complex proteins or peptides that cannot be made by other methods
2) The production of higher yielding crops with superior keeping quality introducing resistance disease
3) The health benefits of treating genetic disease

Question 55

What are the concerns that genetic engineering can introduce?

Answer 55

1) Germ-line gene therapy is controversial as it involves replacing the defective allele with healthy alleles inside the fertilised egg. Some genes have no apparent function other than to control or “switch off” other genes on the same chromosome. Tampering with genes in the fertilised egg could result in unforeseen effects in future generations
2) There are a number of potential hazards associated with genetic engineering and it is impossible to predict what the consequences might be of releasing genetically engineered organisms into the environment

Question 56

What are the potential hazards if genetic engineering?

Answer 56

1) A new gene, on insertion may disrupt normal gene function. For example, a potentially dangerous micro-organism with a new gene may become a dangerous pathogen if it is released into the environment
2) Bacteria readily exchange genetic material. The recombinant DNA might get into other organisms. For example, herbicide resistance might be transferred to a weed species
3) The deliberate use of antibiotic resistant genes in E.coli, which lives in the human gut, and the possibility that these genes could be accidentally transferred to human pathogens
4) The possibility of transfer of DNA with linked pathogenic genes, for example oncogenes increasing cancer risks.