Genetic engineering and biotechnology

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

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).

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

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

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

Gel electrophoresis of DNA is used in DNA profiling.

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

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.

4.4.5 Analyse DNA profiles to draw conclusions about paternity or forensic investigations.

For a suspect look for similarities between the DNA found at the crime scene and the suspect. For a paternity test, look for similarities between the child and the possible father. 

4.4.6 Outline three outcomes of the sequencing of the complete human genome.

  • It is now easier to study how genes influence human development. 
  • It helps identify genetic diseases.
  • It allows the production of new drugs based on DNA base sequences of genes or the structure of proteins coded for by these genes.
  • It will give us more information on the origins, evolution and migration of humans. 

4.4.7 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.

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

4.4.8 Outline a basic technique used for gene transfer involving plasmids, a host cell (bacterium, yeast or other cell), restriction enzymes (endonucleases) and DNA ligase.

The human gene that codes for insulin can be inserted into a plasmid and then this plasmid can be inserted into a host cell such as a bacterium. The bacterium can then synthesis insulin which can be collected and used by diabetics. This is done as follows. The messenger RNA which codes for insulin is extracted from a human pancreatic cell which produces insulin. DNA copies are then made from this messenger RNA by using the enzyme reverse transcriptase and these DNA copies are then given extra guanine nucleotides to the end of the gene to create sticky ends. At the same time, a selected plasmid is cut using restriction enzymes which cut the DNA at specific base sequences. Then extra cytosine nucleotides are added to create sticky ends. Once we have both the plasmid and the gene ready, these are mixed together. The two will link by complementary base pairing (between cytosine and guanine) and then DNA ligase is used to make the sugar phosphate bonds. The plasmids with the human insulin gene (called recombinant plasmids) can then be mixed with host cells such as bacterium. The bacterium will take in the plasmid and start producing insulin which can then be collected and purified.

4.4.9 State two examples of the current uses of genetically modified crops or animals.

  • 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.
  • 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.

4.4.10 Discuss the potential benefits and possible harmful effects of one example of genetic modification.

It is quite common to see genetic modifications in crop plants. An example of this is the transfer of a gene that codes for a protein called Bt toxin from the bacterium Bacillus thuringiensis to maize crops. This is done because maize crops are often destroyed by insects that eat the corn and so by adding the Bt toxin gene this is prevented as the toxin kills the insects. However this is very controversial as even though it has many positive advantages, it can also have some harmful consequences. The table below summarizes the benefits and possible harmful effects of genetically modifying the maize crops. 


Harmful Effects

Since there is less damage to the maize crops, there is a higher crop yield which can lessen food shortages.

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.

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.

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. 

There is a reduction in the use of pesticides which are expensive and may be harmful to the environment, wild life and farm workers. 

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. 

4.4.11 Define clone.

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

4.4.12 Outline a technique for cloning using differentiated animal cells.

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 unfertilized 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.

4.4.13 Discuss the ethical issues of therapeutic cloning in humans.

There are many ethical issues involving therapeutic cloning in humans. Below is a table summarizing the arguments for and against therapeutic cloning in humans. 

Arguments for 

Arguments against

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.

Every human embryo is a potential human being and should be given the chance of developing.

Cells can be taken from embryos that have stopped developing and so these cells would have died anyway. 

More embryos are generally produced than are needed and so many are killed. 

Cells are taken at a stage when the embryos have no nerve cells and so they cannot feel pain.

There is a risk of embryonic stem cells developing into tumour cells.