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Microarrays and bioinformatics

Coordination, Response and Gene Technology · Gene technology · note 4 of 5

Spec 8.20, 8.21
A Level only (what this means)A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels mean
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Microarrays and bioinformaticsSpec 8.20, 8.21

In short

A microarray is a slide with thousands of spots of single-stranded DNA probes. mRNA from a cell is converted to labelled cDNA, which binds to matching probes; fluorescence shows which genes are active. Bioinformatics is the use of computers and software to store, analyse and interpret biological data such as DNA sequences.

Microarrays

A microarray (DNA chip) is a small slide with thousands of tiny spots in a grid. Each spot holds many copies of a single-stranded DNA probe from a known gene. It is used to find out which genes are active (being transcribed) in a tissue at a given time.

  1. mRNA is extracted from the cells being studied (for example cancer cells and normal cells).
  2. Reverse transcriptase makes cDNA from the mRNA, and a fluorescent label is added. Samples from two conditions may carry different colours.
  3. The labelled cDNA is added to the microarray. It binds (hybridises) to the probes with a complementary base sequence.
  4. Unbound cDNA is washed away and the array is scanned. A spot that fluoresces shows the gene was active; the brighter the spot, the more mRNA was present.

Microarrays can identify active genes in different tissues, compare healthy and diseased cells, and show how gene expression changes in response to a drug.

Microarray: a chip of spots with DNA probes, labelled cDNA hybridising to matching probes, and a scanned grid of bright, dull and blank spots with a key. (opens full size in a new tab)
A microarray shows which genes are being expressed.

Bioinformatics

Bioinformatics is the use of computer science, mathematics and statistics to collect, store, analyse and interpret large sets of biological data, such as DNA base sequences, protein sequences and gene expression data. Computers can compare sequences in databases, find genes in a genome and compare species, and so provide a way to handle the very large amount of data produced by sequencing and microarrays.

Exam tip:

Define bioinformatics in terms of computers and biological data. Examples help: comparing a gene sequence in a database to identify its function.

Written and checked against the Edexcel International A Level Biology (YBI11) specification · Updated October 2026

Frequently asked questions

How is recombinant DNA made?

A restriction endonuclease cuts the gene and a plasmid at the same recognition sequence, leaving complementary sticky ends. The gene and plasmid are mixed, so the sticky ends pair by complementary base pairing. DNA ligase then forms phosphodiester bonds between the sugar–phosphate backbones, producing a recombinant plasmid that can be put into a host cell.

What do restriction enzymes and DNA ligase do?

Restriction enzymes (restriction endonucleases) cut DNA at specific base sequences, hydrolysing phosphodiester bonds and often leaving single-stranded sticky ends. DNA ligase does the opposite job, forming phosphodiester bonds to join DNA fragments together. Together they allow a gene to be cut out and joined into a vector.

How are genes put into bacteria and plant cells?

Bacteria take up plasmids after treatment with calcium chloride and a heat shock, which makes their membranes permeable. Plant cells can be transformed by Agrobacterium, which transfers DNA from its Ti plasmid, or by a gene gun that fires DNA-coated metal particles into the cells.

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