Mitosis examples

5.15 - Genetically modified Plants

1. Maize is damaged by the larvae of the European cork borer which can lead up to a 20% loss of crop yield.
2. The bacteria BT has a chromosome which has a gene that can produce "bt toxin" which can kill the cork borer larvae.
3. The first step is to take restriction enzymes to the gene of BT and chop the gene out so that you have the BT gene for the toxin.
4. Then it has to be transferred to the cells of the maize plant. This isn't easy but the technique involved nowadays is a gene gun. 
5. The gene gun takes tiny particles of gold coated with the BT gene and fired at high velocity at the plant cell. This introduces the BT gene to the interior of the plant cell. Therefore the maize cells have the BT gene.
6. When the genes are switched on they will emit the toxin  that can kill the larvae. This gives maize resistance to the damage caused by cork borers

5.14 - Humulin

• A culture of this bacteria will be injected into the fermenter
• It will be necessary to provide this culture:
• Nutrients
• Controlled temperature and pH
• Gases inside the fermenter
• Providing the perfect temperature, pH, gases and the right nutrients will insure optimal growth of the bacteria.
• The population will therefore increase and the bacteria will manufacture the protein Insulin.
• The bacteria inside the fermenter will  manufacture insulin from the nutrient provided (amino acids).
• It will then be necessary to remove the product and carry out purification
• It needs to be purified for human consumption. The ways to purify the insulin is called downstream processing
• The genetically engineered human insulin is called humulin

5.13b - Hosting Recombinant DNA

• Once the recombinant DNA (human gene and bacterial plasmid) is made it is necessary to transfer it to the host cell.
• In this case we will use the virus which consists of nucleic acid (DNA or RNA) and the protein shell (capsid)
• The first thing to do is to remove the nucleic acid from the virus because we only need the capsid.
• The plasmids are then taken up by the virus. The virus acts as the vector of the recombinant DNA
• It is going to help us transfer the DNA into our host cell. The reason we have chosen the virus because that type of virus is known as a phage. What it does is infect bacterial cells. 
• The virus is able to attach to the cell membrane of the bacteria and insert the recombinant DNA into our host cell.
• At the end of this process we have a bacterial cell which now contains the recombinant DNA including the human gene for insulin.

5.13a - Recombinant DNA

The plasmids are found in bacterial cells. They are a ring of DNA and are small and dont carry many genes

A virus has a protein shell (capsid) and inside there'll be a nucleic acid (DNA or RNA). The virus has no other cellular components (such as cytoplasm nucleus)

Human chromosomes consists of DNA. But we will only look at one gene which codes for the protein insulin which is a hormone that controls blood sugar levels.

1. The restriction enzyme is selected that can cut out the gene responsible for insulin.
2. Once the gene is cut we would cut the plasmid with the same restriction enzyme.
3. This would leave the plasmid with the ring structure broken.
4. The next stage is to introduce the human insulin gene into the cut plasmid (the plasmid is composed of DNA, just like the human gene)
5. The plasmid will then be left with the human gene inserted inside of it.
6. It is then necessary to complete the process by applying a 2nd enzyme (DNA ligase) which will join the DNA
7. This combination of the human gene and plasmid DNA is known as recombinant DNA

5.11- Breeding animals

Understand that animals with desired characteristics can be developed by selective breeding.

Example: Cow
Desired: Milk yield

• The earliest farmers noticed that some cows make around 50ml of milk each time they are milk and a few others make 150ml of milk but most of them make 100ml. 
• The farmer will take all the milk but choose to breed only the ones that make 150ml milk
• In the next generation a few cows produce 100ml, 200ml and the majority produce 150ml.
• Of course the farmer take all the milk and select the cows that produce the most milk for breeding
• Perhaps in the next generation the cows will produce 150 to 250 ml of milk.
• The farmers are therefore developing the desired characteristics by selective breeding.
• For this to work the milk yield must be genetic

5.10 Breeding Plants

Understand plants with desired characteristics can be developed by selective breeding.


The number of rice grains is in the control of genes, the farmer wants to improve the number of rice grain per plant (increase the yield). He notices some plants have 6 grains per stem and others have 8 or 10 grains per stem. The farmers decision is to harvest the plants with 6 & 8 grains per plant and use the other grains (10 grains per stem) for planting.

He notices the next generation of rice the grains increased to 8,10 and 12 grains per stem. Therefore he harvest the 8 and 10 grain stems and selects the 12 grain ones for breeding and planting.
In this way the number of grains of rice will gradually increase = yield increases. This is an example of selective breeding