Discuss the use of microarrays in the diagnosis of disease.

a. DNA spots/probes/sequences attached to solid surface/microarray ✔

b. mRNA from healthy tissue/cell isolated and converted to cDNA
OR
mRNA from cancer tissue/cell isolated and converted to cDNA ✔

c. conversion to cDNA by reverse transcriptase ✔

d. fluorescent dye linked to copy DNA/cDNA ✔

e. cancer cDNA colored with a different dye from the healthy cDNA ✔ Accept named colour.

f. cDNA binds to/hybridizes with probes that have complementary base sequences ✔

g. microarray rinsed to remove cDNA that has not hybridized ✔

h. microarray exposed to laser light which causes fluorescent dye to give off light ✔

i. fluorescence shows which probes have hybridized
OR
fluorescence shows which sequences were in the tissue/sample ✔

j. hybridized probe shows gene expression
OR
hybridized probe helps in diagnosis of disease ✔

k. infection by pathogen can be detected by presence of its genetic material ✔

Most candidates had some knowledge of microarrays and could outline the outcome of their usage; some answers nevertheless were not displayed in a very logical order, missing the details of hybridization. Many specified only DNA where cDNA should have been mentioned.