1. A Simple Guide to GMO Testing
Chris Thomas, 2004
Milton Contact Limited at

2. Introducing DNA and where it is found
Plants (and other organisms) are made of cells
Each cell has a nucleus containing DNA
Sometimes the DNA is visible as chromosomes
The DNA contains genes, the basic instructions for a cell and ultimately an organism
Bean seedling
A cell
The nucleus
of the cell
Visible
chromosomes
in a cell

3. What is the difference between Conventional breeding and GMO based breeding?
Parent A is shown with blue chromosomes in a cell.
Parent B is shown with red chromosomes and has a desirable trait.
A is crossed with B.
The progeny contain a mix of chromosomes/genes.
Further crosses of the progeny with Parent A are needed so that only the small amount of B’s DNA with the desired trait remains in the new variety.
GMO based breeding:
A piece of DNA with the specific trait is introduced directly into the parent, creating the desired variety
Conventional breeding
GMO based breeding
Parent
DNA with
specific trait
Desired variety
Parent A
Parent B
progeny
New variety

4. GM DNA inserted into the DNA of a bacterium typically equals ~ 1/200 of the total
Material to be inserted
Bacterial DNA with an insert

5. The GM material inserted into a potato’s DNA, for example, is typically ~ 1/100,000 of the total

6. What is inserted to create a GMO? Using plants as an example
GM DNA inserted into host DNA
Host DNA
Border
fragment
Selectable marker
Gene with
Desired trait
Border
fragment
Host DNA
Host DNA – the DNA of the plant into which the GM material has been introduced
Border fragment – an element needed to aid the insertion the GM DNA
Selectable marker – an element used in the process of making a GM plant
Gene with the desired trait – the actual property or trait, such as a disease resistance

7. Testing for GMOs
GMO testing can be done in two ways: based on the novel protein produced from the inserted gene; based on the inserted GM DNA itself
Protein based testing
Advantages
Simple tests (similar to pregnancy tests)
Rapid (minutes to hours)
Can be used in the field
Specific for a particular protein
Disadvantages
Only works if tissue sampled contains protein
for example, an extract from shoots would not give a result if the protein is only produced in the roots
Detection requires high levels of protein
Will not detect protein in heated or processed samples
DNA based testing
Advantages
Very sensitive
Can be designed to be specific for one GMO
Can be designed to detect a range of GMOs
Can detect DNA if present in processed samples
Can be used to look for and locate the inserted elements in a GMO’s DNA
Disadvantages
Requires specialist laboratories
Can take several days
Prone to false positives

8. A photograph of a simple positive GMO test
Simple DNA testing for presence or absence of a specific GMO DNA insert (PCR)
A photograph of a simple positive GMO test
with a false +ve
The DNA is purified from a specific GMO or sample containing that GMO
A part of the purified GM DNA in the GMO is amplified up to a hundred million times
The GM DNA is then made visible and recorded
The method is qualitative not quantitative, i.e. Yes or No
Even miniscule contamination of solutions and non-GM samples can result in false positives

9. Quantitative DNA testing for presence of specific GMO DNA (Real-time PCR)
Samples = 1, 2, 3
a = high concentration standard
b = medium conc. standard
c = low conc. standard 1 2 3
concentration a b c 4
Threshold value
time
DNA is isolated and amplified as in the previous slide.
The increase of amplified GM DNA is monitored over time, e.g. for samples 1, 2 & 3.
The time at which the amplified DNA level exceeds a threshold level is determined.
The level of GM DNA in sample 1, 2, and 3 is determined by comparison with standards of known GM DNA concentration, a, b, c.
If c is at a level of 0.9% GM DNA, then sample 3 contains less than 0.9% GM DNA, whilst samples 1 and 2 contain more
Sample 4 shows a result seen where the DNA might not have been purified sufficiently and the efficiency of the amplification is reduced leading to a false result

10. Sample size and the Sample’s size
Looking for the presence of low levels of GM material in non-GM grain is also affected by the size of the grain (examples for illustration only – no GM material used or implied). The larger the grain, the greater the weight of material required for testing.
Poppy
Mustard
Rice
Maize/corn

11. The importance of adequate sampling
To ensure that a test gives meaningful results, great care has to be taken. Some factors to consider are:
Is the material you are collecting samples from
Mixed sufficiently to ensure even distribution?
Likely to be contaminated with remnants of a previous storage or processing run – e.g. in grain stores or mills?
Do you need a quick on-site assay looking for presence/absence of GMOs at high level concentrations?
Do you need a precision assay looking for GMOs present above a required low level, that may take several days?
What is the lowest level of GM presence that you need to detect (0.9% or 0.1%)?
How much should be collected for each sample to be representative?
How many samples should be collected each time from a batch of material to give a high probability that any results are statistically significant?
Do you and the testing laboratory have sufficient controls in place to detect false positive or false negative results?

12. In Conclusion
With the introduction of new regulations governing the labelling of products containing GMOs, the need for testing is likely to increase in the future.
Chris Thomas of Milton Contact Limited