ScienceOnline is an interactive resource for students and teachers of science.
The site provides access to a range of activities related to the New Zealand science curriculum for Years 9-11. Both Astronomy and Earth Science have been included as well as the core science areas of Physics, Chemistry and Biology. There are interactive notes and diagrams, self-marking tests, and useful links to other science websites. The site is completely up to date with NCEA requirements at Year 11 with details of achievement standards linked to topics in each of the five subject areas.
ScienceOnline has been developed by Peter Biggs, former science teacher and author of the Blue Science Book, and Sandy McGivern, science teacher, who manages the site.
In this document:
Genetic modification is also called genetic engineering. An organism that has been changed by genetic modification is known as a genetically modified organism (GMO). The first organism to be successfully genetically engineered was a bacteria, in 1977. The first genetically modified plant was produced in 1981 and the first animal in 1988.
Organisms can be genetically modified in three basic ways - by having a gene removed from their DNA, by having a gene inserted into their DNA or by having a gene already in the organism altered in some way. We're going to focus on organisms that have had a gene inserted into their DNA. These organisms are often called transgenic organisms.
Genetic modification for beginners:
Here is a recipe for making a GMO.
- Remove the gene you want to insert from the organism in which it is found.
- Put this gene into a bacterium.
- Make the bacterium grow and reproduce lots so that you get many copies of this gene -one in each bacterium. (You will need lots of copies to keep trying with the next steps!)
- Insert the bacterium with the gene into a cell of the organism to be modified.
- Hope that the bacterium inserts the gene into the DNA of the cell. If it doesn't, go back to step 4.
- When the gene has gone in successfully, grow that genetically modified cell into a whole organism --a GMO.
Here's a little more detail:
How do they get the gene out of the DNA?
Special "molecular scissors" called restriction enzymes are used to cut the desired gene out of the DNA in which it is found. The restriction enzyme is also used to cut open the bacterial DNA. Then, another enzyme is used to "glue" the desired gene into the bacterial DNA. This useful enzyme is called DNA ligase.
When most people hear or read the word "cloning", they think of Dolly the Sheep. In 1997. Dolly was the first cloned animal to be produced. This means that she is genetically identical to another sheep - like an identical twin, only Dolly's "twin" was much older than she is!
So how was Dolly made?
Is your pet irreplaceable? Here's a recipe to make an identical copy so that they may last in your life forever!
- 1. Take a living cell from your beloved pet.
- 2. Get an unfertilised egg from a female of the same species.
- 3. Remove the nucleus from this egg (this removes the genetic information from it).
- 4. Put this and the cell from your pet together and give them a gentle pulse of electricity - if you're lucky, they will fuse together.
- 5. Wait a wee while and then give them a second shot of electricity - if you're really lucky, this will trigger cell division to start. When this starts, you have an embryo that is genetically identical to your pet!
- 6. Find a surrogate mother for the embryo, insert it and wait for your new pet to be born.
Cloning is not actually just about the genetic technique of making an animal that is identical to another one. We have natural clones and gene cloning also.
To understand cloning we need a good definition of "a clone". An organism is a clone when it is genetically identical to another organism. Identical twins are an example of natural clones.
Gardeners make natural clones all the time. Plants have an amazing ability to regenerate an entire plant from one piece of the original plant. Gardeners take cuttings of plants - usually the stem with a few leaves attached - put them in water, and within a few weeks, this piece of plant has sprouted roots and re-grows as a new plant, genetically identical to the original.
(Imagine if you could cut your arm off and grow another you!)
Gene cloning uses much the same techniques as genetic modification - the gene to be cloned is cut out of the DNA in which it belongs and is inserted into a bacterium. Many bacteria have a piece of circular DNA in their cell called a plasmid - this is what the gene is inserted into. The bacteria then grow and divide as normal, but each resulting bacterium also has the new gene in it.
Why clone genes?
Most of the cloning done by Scientists is the cloning of genes. It is essentially a very good way of making large quantities of the desired gene. These are then used for a number of things including:
- Using bacteria as living factories to make proteins. For example, bacteria with the insulin producing gene inserted into them produce most of the insulin used by diabetics. The bacteria produce the insulin as well as carrying out their other bacterial purpose in life and this insulin is collected and purified for use by people.
Bacteria containing a cloned gene are used to try and make genetically modified organisms (GMO's). Making a GMO is hard to do, so lots of copies of the gene are needed for the many attempts at inserting it into another organism.
- Using bacteria with genes inserted to do jobs that couldn't be done before. For example, there are bacteria that have a gene inserted into them that are capable of digesting oil. These bacteria are used for cleaning up oil spills.
- Bacteria with genes inserted are also used for storing genes of particular interest - these are called gene libraries. This has been particularly useful in the Human Genome Project. This recently completed research has mapped and sequenced the entire DNA in human beings. The interesting parts are all stored in the gene libraries along with many other genes from other organisms.
Stem cell research
Stem cells are cells that are able to divide continuously and develop into different types of tissues. A stem cell can become a heart, liver, big toe etc! Non-stem cells, such as a liver cell, will not under any circumstances divide and change into something else - it will only ever be able to make more liver cells.
Stem cell technology is a very new field of genetic research. The Scientists involved are hoping that stem cells can be grown particular tissues or organs from transplantation into people, or for gene therapy (a very new technology that may one day be able to treat people with genetic disorders and cure them).
Where do stem cells come from?
Stem cell research is quite controversial as stem cells are most easily obtained from embryos and foetuses from pregnancy terminations (abortions). Many people object to research using these sources. Stem cells are also now being extracted from umbilical cords and bone marrow.
In 1986 DNA fingerprinting was invented. This technique is based on the fact that every one has unique DNA and can therefore be identified through their DNA. DNA fingerprinting is also known as DNA profiling.
What is DNA fingerprinting used for?
DNA fingerprinting is used mainly in police forensics work, to help solve violent crime. It is also used in paternity cases where it is uncertain who the father of a child is. This technique is far more accurate than previous techniques using blood groupings.
How is DNA fingerprinting carried out?
|Only a small sample of DNA is needed for DNA fingerprinting - a hair or a semen sample is plenty. A special process called PCR is used to copy this DNA millions of times so that the scientists have plenty of copies to work with. It is vital that the sample of DNA is not contaminated with someone else's DNA before doing this (even the dandruff from the technicians' hair would contaminate the sample irreversibly!)
|The DNA is cut at particular parts known to be unique to everyone. These parts are very special because they are different lengths. The cut DNA is sorted out into lengths, giving it a barcode-like appearance. Each bar represents a particular length of DNA and the thickness of the bar indicates how much of that length DNA there is. The barcode (DNA fingerprint) is then compared to the suspect's fingerprint and if they match, the DNA must be the same. (Which, unless they have an identical twin, means that the DNA was probably theirs!)
|In paternity cases the DNA fingerprints of the possible fathers are compared with the child's and mother's DNA fingerprints. Half the DNA of the child should match half of that from the mother and the other half is used to see if there is a close match with any of the potential fathers. Only half of the father's DNA will match with half of the child's DNA. |