Which of the following pairs is correctly matched?

The correct answer is Option (3) → Monocistronic structural genes – mostly in eukaryotes

A cistron is a segment of DNA coding for a polypeptide. A structural gene is monocistronic when it codes for one polypeptide (mostly in eukaryotes) and polycistronic when it codes for several (mostly in bacteria or prokaryotes). The monocistronic genes of eukaryotes are split: their exons are interrupted by introns.

Option (1) Split genes – mostly in prokaryotes — Incorrect. Split genes are a feature of eukaryotes. The genes of prokaryotes are not interrupted by introns.

Option (2) Polycistronic structural genes – mostly in eukaryotes — Incorrect. Polycistronic structural genes are found mostly in bacteria or prokaryotes, as in the lac operon. Eukaryotic genes are mostly monocistronic.

Option (3) Monocistronic structural genes – mostly in eukaryotes — Correct. In eukaryotes the structural gene in a transcription unit is mostly monocistronic, so this pair is correct.

Option (4) Exons – sequences that do not appear in mature RNA — Incorrect. Exons are the coding sequences that do appear in mature or processed RNA. The sequences that do not appear in it are the introns.

NCERT Extract:
Transcription Unit and the Gene – “… However by defining a cistron as a segment of DNA coding for a polypeptide, the structural gene in a transcription unit could be said as monocistronic (mostly in eukaryotes) or polycistronic (mostly in bacteria or prokaryotes). In eukaryotes, the monocistronic structural genes have interrupted coding sequences – the genes in eukaryotes are split. The coding sequences or expressed sequences are defined as exons. Exons are said to be those sequence that appear in mature or processed RNA. The exons are interrupted by introns. Introns or intervening sequences do not appear in mature or processed RNA.”