Gene Probes


Gene probes are short sequences of single stranded DNA (or RNA) that have been radioactively labelled

  • Being single stranded they can bind to a complementary sequence if present
  • Gene probes are commonly used to screen for mutant alleles that cause disease and one way of doing this is via DNA microarrays

DNA Microarrays

  • Genetic disorders can be screened using a DNA microarray - a collection DNA spots / probes (representing genes) embedded on a solid matrix
  • A single microarray can contain 10,000 or more probes and can hold representative fragments from the entire genome
  • To determine which genes are being expressed by cells (including those responsible for disease), the following steps are conducted:
    • mRNA from the cell is converted into copy DNA fragments (cDNA) by the enzyme reverse transcriptase
    • The cDNA fragments are attached to a fluorescent dye or are radioactively labelled and then are added to the microarray¬†
    • cDNA fragments will bind to their specific probe (via complementary base pairing) and remain fixed when unattached fragments are washed away¬†
    • The wells that still fluoresce after washing contain fragments that represent mRNA being expressed within the cell
    • Comparing the genes being expressed in a normal individual versus a sick individual can provide clues as to the cause of disease

Overview of DNA Microarrays