The following schematic graph shows the result of two quantitative RT-PCR experiments. Total mRNA from two tissue samples (1 and 2) was isolated and subjected to RT-PCR using primers designed to amplify a tissue-specific gene. Added to the reaction was a fluorescent dye that fluoresces only when bound to double-stranded DNA. According to the graph, which tissue has a higher level of this mRNA? By how much?
A) About 2-fold higher in tissue 1
B) About 1000-fold higher in tissue 1
C) About 2-fold higher in tissue 2
D) About 1000-fold higher in tissue 2

Question

The following schematic graph shows the result of two quantitative RT-PCR experiments. Total mRNA from two tissue samples (1 and 2) was isolated and subjected to RT-PCR using primers designed to amplify a tissue-specific gene. Added to the reaction was a fluorescent dye that fluoresces only when bound to double-stranded DNA. According to the graph, which tissue has a higher level of this mRNA? By how much? 
A) About 2-fold higher in tissue 1 
B) About 1000-fold higher in tissue 1 
C) About 2-fold higher in tissue 2 
D) About 1000-fold higher in tissue 2

Quizplus · Accepted Answer

The sample with a higher concentration of mRNA requires fewer PCR cycles to reach the same half-maximal DNA concentration. A difference of about 10 cycles corresponds to an approximately 1000-fold difference in mRNA level (2¹⁰ = ~1000).

The Following Schematic Graph Shows the Result of Two Quantitative