Question

You transcribe a gene and obtain mRNA. To detect which strand is transcribed you replicate each strand in vitro and use the newly synthesized strand for hybridization with mRNA. If mRNA hybridize with the newly replicated strand from 1^st strand then the gene transcribed was in ________

(a) 1^st strand

(b) 2^nd strand

(c) Same copy in both strands

(d) Dispersed

The question was posed to me during a job interview.

Question is taken from Transcription in Prokaryotes : Sigma Factor topic in section Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

Right choice is (b) 2^nd strand

Best explanation: mRNA produced from 1^st strand and DNA produced by replicating 1^st strand should have the same sequence and they will not hybridize. However, if the gene is transcribed from 2^nd strand then this result is possible. RNA pol only transcribes one strand at a time so dispersed and both being transcribed are not possible.