A messenger RNA from a human gene that is 4 kb in length is used as a probe in a Southern blot to identify restriction fragments of chromosomal DNA to which the mRNA can hybridize. Restriction fragments of DNA of 4 kb and 5 kb are observed to hybridize with the mRNA probe. What could explain how a 4 kb probe can hybridize with fragments that together sum to 9 kb?
A)The gene from which the mRNA probe is transcribed may contain one or more introns.
B)A restriction fragment may extend beyond the 5' end of the transcription start site.
C)A restriction fragment may extend beyond the 3' end of the transcription stop site.
D)The gene from which the mRNA probe is transcribed may contain introns, or the restriction fragments may extend beyond the 5' or 3' ends of the transcription stop site.
E)The result must be some sort of mistake.

Question

Quizplus · Accepted Answer

The gene from which the mRNA probe is transcribed may contain introns, or the restriction fragments may extend beyond the 5' or 3' ends of the transcription stop site. This could result in fragments larger than the actual mRNA length that still contain the sequence recognized by the probe. Therefore, both introns and extension of the restriction fragments could account for the difference between the observed hybridization size and the actual mRNA size.

A Messenger RNA from a Human Gene That Is 4