4.4 Genetic Engineering and Biotechnology


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

PCR is a way of producing large quantites of a specific target sequence of DNA

It is useful when only a small amount of DNA is avaliable for testing 

  • E.g. crime scene samples of blood, semen, tissue, hair, etc.

PCR occurs in a thermal cycler and involves a repeat procedure of 3 steps:

1.  Denaturation:  DNA sample is heated to separate it into two strands

2.  Annealing:  DNA primers attach to opposite ends of the target sequence

3.  Elongation:  A heat-tolerant DNA polymerase (Taq) copies the strands 

One cycle of PCR yields two identical copies of the DNA sequence

  • A standard reaction of 30 cycles would yield 1,073,741,826 copies of DNA (230)

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

Gel electrophoresis is a technique which is used to separate fragments of DNA according to size

  • Samples of fragmented DNA are placed in the wells of an agarose gel
  • The gel is placed in a buffering solution and an electrical current is passed across the gel
  • DNA, being negatively charged (due to phosphate), moves to the positive terminus (anode)
  • Smaller fragments are less impeded by the gel matrix and move faster through the gel
  • The fragments are thus separated according to size 
  • Size can be calculated (in kilobases) by comparing against a known industry standard

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

  • DNA profiling is a technique by which individuals are identified on the basis of their respective DNA profiles
  • Within the non-coding region of an individual's genome, there exists satellite DNA - long stretches of DNA made up of repeating elements called short tandem repeats (STRs)
  • These repeating sequences can be excised to form fragments, by cutting with a variety of restriction endonucleases (which cut DNA at specific sites)
  • As individuals all have a different number of repeats in a given sequence of satellite DNA, they will all generate unique fragment profiles
  • These different profiles can be compared using gel electrophoresis

DNA Profiling Using STR Analysis

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

  • A DNA sample is collected (blood, saliva, semen, etc.) and amplified using PCR
  • Satellite DNA (non-coding) is cut with specific restriction enzymes to generate fragments
  • Individuals will have unique fragment lengths due to the variable length of their short tandem repeats (STR)
  • The fragments are separated with gel electrophoresis (smaller fragments move quicker through the gel)
  • The DNA profile can then be analysed according to need

Two applications of DNA profiling are:

  • Paternity testing (comparing DNA of offspring against potential fathers)
  • Forensic investigations (identifying suspects or victims based on crime-scene DNA)  

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

Paternity Testing:  Children inherit half of their alleles from each parent and thus should possess a combination of their parents alleles

Forensic Investigation:  Suspect DNA should be a complete match with the sample taken from a crime scene if a conviction is to occur

                                                     Paternity Test                                                                                                           Forensic Investigation

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

The Human Genome Project (HGP) was an international cooperative venture established to sequence the 3 billion base pair (~25,000 genes) in the human genome 

The outcomes of this project include:

  • Mapping:  We now know the number, location and basic sequence of human genes
  • Screening:  This has allowed for the production of specific gene probes to detect sufferers and carriers of genetic disease conditions
  • Medicine:  With the discovery of new proteins and their functions, we can develop improved treatments (pharmacogenetics and rational drug design)
  • Ancestry:  It will give us improved insight into the origins, evolution and historical migratory patterns of humans 

With the completion of the Human Genome Project in 2003, researcher have begun to sequence the genomes of several non-human organisms

In Situ Hybridisation

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

The genetic code is universal, meaning that for every living organism the same codons code for the same amino acids (there are a few rare exceptions)

This means that the genetic information from one organism could be translated by another (i.e. it is theoretically transferable) 

Current Examples of Transgenic Modification

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

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

Treating Haemophilia via the Isolation of Human Factor IX Clotting Protein from Transgenic Sheep Milk

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


1.  Engineering crops to extend shelf life of fresh produce

  • Tomatoes (Flavr Savr) have been engineered to have an extended keeping quality by switching off the gene for ripening and thus delaying the natural process of softening of fruit

2.  Engineering of crops to provide protection from insects

  • Maize crops (Bt corn) have been engineered to be toxic to the corn borer by introducing a toxin gene from a bacterium (Bacillus thuringiensis


1.  Engineering animals to enhance production

  • Sheep produce more wool when engineered with the gene for the enzyme responsible for the production of cysteine - the main amino acid in the keratin protein of wool

2.  Engineering animals to produce desired products

  • Sheep engineered to produce human alpha-1-antitrypsin in their milk can be used to help treat individuals suffering from hereditary emphysema

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

Example:  Maize introduced with a bacterial gene encoding a toxin to the European Corn Borer (i.e. Bt Corn)

Potential Benefits

  • Allows for the introduction of a characteristic that wasn't present within the gene pool (selective breeding could not have produced desired phenotype)
  • Results in increased productivity of food production (requires less land for comparable yield)
  • Less use of chemical pesticides, reducing the economic cost of farming
  • Can now grow in regions that, previously, may not have been viable (reduces need for deforestation)

Potential Harmful Effects

  • Could have currently unknown harmful effects (e.g. toxin may cause allergic reactions in a percentage of the population)
  • Accidental release of transgenic organism into the environment may result in competition with native plant species
  • Possibility of cross pollination (if gene crosses the species barrier and is introduced to weeds, may have a hard time controlling weed growth)
  • Reduces genetic variation / biodiversity (corn borer may play a crucial role in local ecosystem)

4.4.11  Define clone

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

4.4.12  Outline a technique for cloning using differentiated animal cells

Somatic Cell Nuclear Transfer (SCNT) is a method of reproductive cloning using differentiated animal cells

  • A female animal (e.g. sheep) is treated with hormones (such as FSH) to stimulate the development of eggs
  • The nucleus from an egg cell is removed (enucleated), thereby removing the genetic information from the cell
  • The egg cell is fused with the nucleus from a somatic (body) cell of another sheep, making the egg cell diploid
  • An electric shock is delivered to stimulate the egg to divide, and once this process has begun the egg is implanted into the uterus of a surrogate
  • The developing embryo will have the same genetic material as the sheep that contributed the diploid nucleus, and thus be a clone

Different Uses of Cloning

4.4.13  Discuss the ethical issues of therapeutic cloning in humans

  • Refer to Topic 2.1.10 for an outline of uses for therapeutic cloning in humans

Arguments for Therapeutic Cloning

  • May be used to cure serious diseases or disabilities with cell therapy (replacing bad cells with good ones)
  • Stem cell research may pave the way for future discoveries and beneficial technologies that would not have occurred if their use had been banned
  • Stem cells can be taken from embryos that have stopped developing and would have died anyway (e.g. abortions)
  • Cells are taken at a stage when the embryo has no nervous system and can arguably feel no pain

Arguments Against Therapeutic Cloning

  • Involves the creation and destruction of human embryos (at what point do we afford the right to life?)
  • Embryonic stem cells are capable of continued division and may develop into cancerous cells and cause tumors
  • More embryos are generally produced than are needed, so excess embryos are killed
  • With additional cost and effort, alternative technologies may fulfil similar roles (e.g. nuclear reprogramming of differentiated cell lines)