Brent Cornell

    
Individuals can be screened for genetic diseases and cancers by using cDNA and microarrays

• This technology can also be used to investigate the protein expression pathways that lead to these conditions

cDNA

Complementary DNA (cDNA) is a molecule synthesised from an mRNA template via reverse transcription

• cDNA molecules represent gene sequences that are actively transcribed by a cell (as they were synthesised from mRNA) 
• This makes them a valuable tool for determining expression patterns of proteins in normal and diseased states

Microarray

A DNA microarray is a collection of microscopic DNA sequences (oligos) attached to a solid surface

• These sequences represent fractions of a large library of genes that are present in a cell
• If a gene is active within a cell, then the cDNA (produced from the mRNA transcript) will bind to its complementary oligo
• If the cDNA has been fluorescently labeled, then the complementary oligo can be identified 
• Each oligo represents a known gene sequence, so genetic diseases are identified according to which oligos are hybridised
• The greater the expression of a particular gene, the brighter the fluorescence seen in the relevant microarray well

In addition to diagnosing genetic diseases, microarrays can also be used to identify new genes that cause disease conditions

• If cDNA from healthy and diseased cells are labeled with different fluorophores, comparisons of gene expression can be made
• Genes that are only active in a diseased or normal state will be of particular interest to scientists

DNA Microarray Overview

    
When microarrays are used to compare mRNA expression in healthy and diseased cells, the following conventions are used:

• cDNA from healthy cells are typically tagged with green fluorescence, while cDNA from diseased cells are tagged with red
• This enables identification of genes present only in healthy cells (green), diseased cells (red), both (yellow) or neither (none)

Microarray Analysis  (click on the diagram to solve)