4.4: Genetic engineering & biotechnology

Question 1

Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA.

Answer 1

Polymerase chain reaction is used to copy and amplify minute quantities of DNA. It can be useful when only a small amount of DNA is available but a large amount is required to undergo testing. We can use DNA from blood, semen, tissues and so on from crime scenes for example. The PCR requires high temperature and a DNA polymerase enzyme from Thermus aquaticus (a bacterium that lives in hot springs).

Question 2

State that, in gel electrophoresis, fragments of DNA move in an electric field and are separated according to their size.

Answer 2

In gel electrophoresis, fragments of DNA move in an electrical field and are separated according to their size.

Question 3

State that gel electrophoresis of DNA is used in DNA profiling.

Answer 3

Gel electrophoresis of DNA is used in DNA profiling.

Question 4

Describe the application of DNA profiling to determine paternity and also in forensic investigations.

Answer 4

Organisms have short sequences of bases which are repeated many times. These are called satellite DNA. These repeated sequences vary in length from person to person. The DNA is copied using PCRand then cut up into small fragments using restriction enzymes. Gel electrophoresis separates fragmented pieces of DNA according to their size and charge. This gives a pattern of bands on a gel which is unlikely to be the same for two individuals. This is called DNA profiling. DNA profiling can be used to determine paternity and also in forensic investigations to get evidence to be used in a court case for example.

Question 5

Outline 3 outcomes of the sequencing of the complete human genome:

Answer 5

1. It is now easier to study how genes influence human development.
2. It helps identify genetic diseases.
3. It will give us more information on the origins, evolution and migration of humans.

Question 6

State that, when genes are transferred between species, the amino acid sequence of polypeptides translated from them is unchanged because the genetic code is universal.

Answer 6

When genes are transferred between species, the amino acid sequence of polypeptides translated from them is unchanged because the genetic code is universal.

Question 7

Outline a basic technique used for gene transfer involving plasmids, a host cell, restriction enzymes and DNA ligase.

Answer 7

1. DNA Extraction:
   - A plasmid is removed from a bacterial cell (plasmids are small, circular DNA molecules that can exist and replicate autonomously)
   - A gene of interest is removed from an organism’s genome using a restriction endonuclease which cut at specific sequences of DNA
   - The gene of interest and plasmid are both amplified using PCR technology
2. Digestion and Ligation
   - The plasmid is cut with the same restriction enzyme that was used to excise the gene of interest
   - Cutting with certain restriction enzymes may generate short sequence overhangs (“sticky ends”) that allow the the two DNA constructs to fit together
   - The gene of interest and plasmid are spliced together by DNA ligase creating a recombinant plasmid
3. Transfection and Expression
   - The recombinant plasmid is inserted into the desired host cells (this is called transfection for eukaryotic cells and transformation for prokaryotic cells)
   - The transgenic cells will hopefully produce the desired trait encoded by the gene of interest (expression)
   - The product may need to subsequently be isolated from the host and purified in order to generate sufficient yield.

Question 8

State two examples of current users of genetically modified crops or animals.

Answer 8

1. The transfer of a gene for factor IX which is a blood clotting factor, from humans to sheep so that this factor is produced in the sheep’s milk.
2. The transfer of a gene that gives resistance to the herbicide glyphosate from bacterium to crops so that the crop plants can be sprayed with the herbicide and not be affected by it.

Question 9

Discuss the potential benefits and possible harmful effects on one example of genetic modification:

Answer 9

Benefits:

• Since there is less damage to the maize crops, there is a higher crop yield which can lessen food shortages.
• Since there is a higher crop yield, less land is needed to grow more crops. Instead the land can become an area for wild life conservation.
• There is a reduction in the use of pesticides which are expensive and may be harmful to the environment, wild life and farm workers.

Harmful effects:

• We are not sure of the consequences of humans and animals eating the modified crops. The bacterial DNA or the Bt toxin itself could be harmful to human as well as animal health.
• Other insects which are not harmful to the crops could be killed. The maize pollen will contain the toxin and so if it is blown onto near by plants it can kill the insects feeding on these plants.
• Cross pollination can occur which results in some wild plants being genetically modified as they will contain the Bt gene. These plants will have an advantage over others as they will be resistant to certain insects and so some plants may become endangered. This will have significant consequences on the population of wild plants.

Question 10

Define clone:

Answer 10

A group of genetically identical organisms or a group of genetically identical cells derived from a single parent cell.

Question 11

Outline a technique for cloning using differentiated animal cells.

Answer 11

Dolly the sheep was cloned by taking udder cells from a donor sheep. These cells were than cultured in a low nutrient medium to make the genes switch off and become dormant. Then an unfertilised egg was taken from another sheep. The nucleus of this egg cell was removed by using a micropipette and then the egg cells were fused with the udder cells using a pulse of electricity. The fused cells developed like normal zygotes and became embryos. These embryos were then implanted into another sheep who’s role was to be the surrogate mother. One lamb was born successfully and called Dolly. Dolly was genetically identical to the sheep from which the udder cells were taken.

Question 12

Discuss the ethical issues of therapeutic cloning in humans.

Answer 12

Arguments for:

• Embryonic stem cells can be used for therapies that save lives and reduce pain for patients. Since a stem cell can divide and differentiate into any cell type, they can be used to replace tissues or organs required by patients.
• Cells can be taken from embryos that have stopped developing and so these cells would have died anyway.
• Cells are taken at a stage when the embryos have no nerve cells and so they cannot feel pain.

Arguments against:

• Every human embryo is a potential human being and should be given the chance of developing.
• More embryos are generally produced than are needed and so many are killed.
• There is a risk of embryonic stem cells developing into tumour cells.