Transgenic

The word transgenic is built from two parts: 'trans' meaning across (as in 'transfer'), and 'genic' meaning to do with genes. Put together, transgenic describes the transfer of genetic material from one species to a different species.

A transgenic organism is therefore an organism that contains a gene taken from another species. That foreign gene becomes part of the organism's DNA, and it is then passed on when the organism reproduces.

Two ideas are essential here:

• The gene comes from a different species — for example a human gene placed into a bacterium, or a bacterial gene placed into a plant.
• The transferred gene still works in its new host: it codes for the same protein as it did in the original species. This is possible because the genetic code is universal — the same DNA bases code for the same amino acids in (almost) all living things.

Exam tip. The single most important phrase to learn is that transgenic means 'transfer of genetic material / a gene from one species to a different species'. The words different species are what earn the mark.

Transgenic organisms are created by genetic modification (also called genetic engineering). This is the process of deliberately moving a gene from one organism and inserting it into the DNA of another.

In simple terms, the steps are:

1. Identify and cut out the wanted gene from the DNA of one species (the donor).
2. Insert that gene into the DNA of a different species (the host).
3. The host now contains a gene from another species — it is transgenic.
4. When the host reproduces, the new gene is passed on to its offspring.

Because the host has a gene from a different species, it can make a new protein that it could not make before. That is the whole point of making a transgenic organism — to give it a useful new characteristic.

You can picture the transfer like this:

Exam tip. Link the words together: transgenic organisms are made by genetic modification / genetic engineering, by transferring a gene from one species into a different species.

You should be able to give clear examples of transgenic organisms. The two most useful for the exam are:

1. Bacteria with the human insulin gene. The human gene for insulin is transferred into bacteria. The bacteria are now transgenic — they contain a human gene. Because the genetic code is universal, the bacteria can read this gene and make human insulin. The bacteria are grown in huge numbers, and the insulin they produce is collected and used to treat people with diabetes. This gives a reliable supply of human insulin.

2. Crops with a bacterial gene. A useful gene from a bacterium can be transferred into a crop plant. For example, a bacterial gene can be added to make a crop resistant to insect pests or able to tolerate a herbicide. The crop is now transgenic — it contains a gene from a different species (a bacterium). This can increase the yield of the crop.

Notice the pattern in both examples:

• A gene is taken from one species (human, bacterium).
• It is placed into a different species (bacterium, plant).
• The new organism is transgenic and can make a new, useful protein.

Exam tip. When asked for an example, always make the two different species clear — e.g. 'a human gene transferred into a bacterium' or 'a bacterial gene transferred into a crop plant'. Just saying 'insulin' without naming the species transfer can miss the mark.

A very common exam task is to distinguish transgenic organisms from selective breeding. They both change an organism's characteristics, but in completely different ways.

Selective breeding means choosing organisms with desired features and breeding them together over many generations, so the desired features become more common. Crucially, the organisms bred together must be the same species — for example breeding cows that produce a lot of milk with other high-yield cows, or breeding wheat with a high grain yield. No gene is moved from one species to another; the genes already exist within that single species.

Transgenic organisms are made by genetic modification: a gene is transferred from one species into a completely different species. So a transgenic organism contains a gene that could not have got there by ordinary breeding, because it came from a different species.

The key difference to remember:

	Selective breeding	Transgenic (genetic modification)
Species involved	Same species only	Two different species
How it works	Choose and breed organisms together	Transfer a gene between species
Speed	Slow — takes many generations	Fast — gene added directly
Example	High-milk cows bred together	Human insulin gene put into bacteria

Exam tip. The discriminating point is the species: selective breeding only ever uses the same species, while a transgenic organism contains a gene from a different species. State this difference clearly to earn the mark.