Question

An intervening sequence in a eukaryotic gene that is not an active part of the gene is called a
A. Exon
B. Intron
C. Replicon
D. None of these

Answer 1

All the genetic information of a living organism is stored in the nucleus of its cells. The nucleus contains the genetic material of an organism in the form of DNA. DNA carries all the genetic structure of an organism. It is responsible for the inheritance of the genetic characters from parents to offspring.

Complete answer:
The DNA segment-first undergoes the replication process and further transcription and translation occur. The smallest segment of DNA that undergoes replication is called a replicon. Cistron is the term used for the DNA segment which is responsible for the polypeptide chain synthesis.
DNA molecules undergo the transcription process segment-wise. A particular DNA segment which is to be transcripted is called a transcription unit. The transcription unit which is further responsible for the synthesis of the single polypeptide chain is called a monocistronic unit and the unit which synthesizes many polypeptide chains is called a polycistronic unit.
In eukaryotes, the monocistronic structural genes have interrupted coding sequences. These types of genes are called a split gene. The sequence in the split gene which undergoes translation and forms a polypeptide chain is called an exon sequence. These are expressed in the mature and processed RNA. But the sequence which does not appear in processed and mature RNA is called an intron sequence. These are the intervening sequences in between the exons.
Thus the correct answer is B.

Note: Most of the prokaryotic genes are non-split while most of the eukaryotic genes are split genes. The presence of introns in the RNA leads to the formation of an immature RNA called pre-mRNA. The process called splicing is responsible for the removal of introns from the pre-mRNA and thus a mature RNA is formed having only the functional sequences called exons.