• Gene markers are used to identify whether a gene has been take up b y a bacterial cell
  • They all require a secondary separate gene to be used

Antibiotic Resistance Marker

  • Replica Plating refers to the identification of cells with plasmids that have take up the new gene
  • Replica plating is the process which utilises the other antibiotic resistance gene in the plasmid which cuts in order to incorporate the required gene
  • Bacterial cells which survived treatment with ampicillin (antibiotic) are known to have take up the plasmid
  • These cells are cultured by spreading them on a nutrient agar plate
  • Each sperate cell on the plate will grow into a genetically identical colony
  • A small sample of each colony is transferred onto a secondary (replica) plate in the same position as the colonies on the original plate
  • The replica plate contains a different antibiotic (tetracycline) against which the antibiotic-resistance gene will have not been disabled if the new gene has been take up
  • The colonies killed by tetracycline must be ones that have take up the required gene
  • Colonies in the same position on the original plate are the ones that posses the required gene these colonies are therefore, made up of bacteria that have been genetically modified and have been transformed

Fluorescent Markers

  • A gene taken from a jelly fish results in a green fluorescent protein (GFP)
  • The gene is cloned and inserted into the centre of the GFP gene
  • Any bacterial cell that has take up the plasmid with the gene that is to be cloned will not be able to produce GFP
  • The cells that have taken up the gene will not fluoresce
  • As the bacterial cells with the desired gene are not killed, there is no need for replica plating
  • Results can be obtained by viewing the ceclls under a microscope and retaining those which do not fluoresce
  • Process is more rapid

Enzyme Marker

  • Lactase will turn a colourless solution substrate into blue
  • The required gene is transplanted into a gene which produces lactase
  • If a plasmid with a required gene is present in a bacterial cells the colonies grown from it will not produce lactase
  • When these bacterial cells are grown in the colourless substrate solution they will be unable to change the solution to blue
  • The bacteria which did not obtain the gene will turn the substrate blue.