| Date | May 2018 | Marks available | 2 | Reference code | 18M.3.HL.TZ2.11 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Explain | Question number | 11 | Adapted from | N/A |
Question
A DNA microarray chip was prepared as a collection of microscopic DNA strands from human genes attached to a solid surface. The diagram shows part of the microarray chip after hybridization with cDNA produced from normal cells and from cancer cells. cDNA of normal cells was labelled with green fluorescent dye and cDNA from cancer cells was labelled with red fluorescent dye. Both sets of labelled cDNA were then allowed to bind to the microarray.
Explain the reason that only cDNA from expressed genes binds to the DNA on the chip.
Explain how the information obtained in this microarray accounts for the differences between normal cells and cancer cells.
Markscheme
a. mRNA is purified from «normal and cancer» cells
b. only expressed/transcribed genes produce mRNA
c. cDNA is «a complementary DNA copy» synthesized from mRNA «by using reverse transcriptase/transcription»
a. red spots are genes only expressed in cancer cells
b. green spots are genes only expressed in normal cells
c. yellow spots mean that genes are expressed in both normal and cancer cells
d. red spots mean that this gene is missing/not active in normal cells
OR
those «red spot» genes could be promoting cancer growth
e. green spots mean that this gene is missing in cancer cells
OR
missing genes could be an inhibitor of cancer
