A level-readyAll subjects · Biology · WBI15 (Unit 5)
Microarrays, bioinformatics and the GM debate
Microarrays show which genes are active in a cell, and bioinformatics makes sense of enormous amounts of biological data. GM organisms bring benefits and risks that society must weigh.
DNA microarrays
A microarray is a small slide with thousands of spots, each containing many copies of a known single-stranded DNA probe for one gene.
1. mRNA is extracted from the cells being studied (only active genes are transcribed).
2. Reverse transcriptase makes cDNA, which is labelled with a fluorescent dye.
3. The labelled cDNA is washed over the microarray and hybridises (binds by complementary base pairing) to matching probes.
4. Unbound cDNA is washed off and the slide is scanned. Fluorescent spots show which genes were active; brighter spots mean more mRNA.
Two samples (for example healthy and cancerous tissue) can be labelled with different coloured dyes and compared on one array, showing which genes are switched on or off in disease.
Bioinformatics
Bioinformatics is the development and use of computer software to store, organise and analyse biological data, such as DNA and protein sequences and protein structures.
Uses include: storing genome sequences in shared databases; searching for genes and comparing sequences between species to work out evolutionary relationships; identifying mutations linked to disease; predicting protein structure from a base sequence; and analysing microarray results.
Risks and benefits of GMOs
Decisions about GM organisms weigh possible benefits against possible risks, using evidence from trials and monitoring.
| Benefits | Risks and concerns |
|---|---|
| Higher crop yields and less land needed | Genes may spread to wild relatives (for example creating herbicide-resistant weeds) |
| Pest resistance (such as Bt crops) reduces insecticide spraying | Harm to non-target insects; pests may evolve resistance |
| Herbicide tolerance allows easier weed control | More herbicide use; reduced biodiversity in fields |
| Improved nutrition (such as Golden Rice with beta-carotene) | Possible unknown effects on health, such as allergies |
| Production of medicines such as insulin | Ethical and economic concerns: patents, seed costs, farmers dependent on large companies |
Worked example
Explain how a microarray can show which genes are expressed in cancer cells but not in healthy cells.
- Extract mRNA from both cell types and make cDNA with reverse transcriptase.
- Label cancer cDNA with one fluorescent dye and healthy cDNA with another.
- Both hybridise to probes on the same array; the colour of each spot shows which sample contained that mRNA.
Answer: Spots showing only the cancer dye colour are genes active in cancer cells but not in healthy cells.
Check yourself
- What is attached to each spot on a DNA microarray?
- Antibodies against one protein
- Whole chromosomes
- Restriction enzymes
- Many copies of a single-stranded DNA probe for one gene
Show answer
Many copies of a single-stranded DNA probe for one gene. Probes hybridise with complementary cDNA.
- Why is mRNA extracted from cells for a microarray, rather than DNA?
- mRNA is more stable than DNA
- Only active genes are transcribed into mRNA
- DNA cannot be labelled
- Cells do not contain DNA
Show answer
Only active genes are transcribed into mRNA. mRNA shows which genes are being expressed.
- What happens when labelled cDNA hybridises on a microarray?
- It is cut by restriction enzymes
- It is translated into protein
- It replicates on the slide
- It binds to complementary probes by base pairing
Show answer
It binds to complementary probes by base pairing. Complementary base pairing holds it in place.
- What is bioinformatics?
- The use of computer software to store and analyse biological data
- The study of living organisms in their habitats
- A method of inserting genes into plants
- A type of brain scan
Show answer
The use of computer software to store and analyse biological data. Computing applied to biological data such as sequences.
- What is a benefit of Bt crops that make an insecticidal protein?
- They need more insecticide
- They cannot be eaten by any animal
- Less insecticide needs to be sprayed
- They never need water
Show answer
Less insecticide needs to be sprayed. The plant protects itself from certain insect pests.
- Which is an environmental risk of growing herbicide-tolerant GM crops?
- The tolerance gene could spread to wild relatives, creating resistant weeds
- The crop will have a lower yield
- The crop cannot be sprayed at all
- It makes the soil radioactive
Show answer
The tolerance gene could spread to wild relatives, creating resistant weeds. Cross-pollination may transfer the gene.
- Which is an economic or ethical concern about GM crops?
- GM crops cannot be patented
- GM crops are always cheaper
- Farmers may depend on large companies for patented seed
- GM crops contain no DNA
Show answer
Farmers may depend on large companies for patented seed. Patents and seed costs raise fairness concerns.
Sources
Last updated 7 November 2026. Spotted a mistake? Tell us.