Introns are best described as which of the following?

• A. The Part That Codes For Proteins
• B. The Expressed Part of the Gene
• C. Coding Sequence That Is Spliced
• D. Part of the DNA Sequence That Isn't Expressed

Answer: (D)

Introns are noncoding segments within a gene that are transcribed into RNA but are removed from the final mRNA before protein production. They lie between the coding regions (exons), and during RNA processing the introns are spliced out, leaving exons to be joined together to form the mature mRNA that will be translated. Because introns do not code for amino acids and are not present in the final expressed transcript, they fit the description of a part of the DNA sequence that isn’t expressed. The other descriptions misidentify introns as coding regions or as the parts that remain after splicing; those roles belong to exons. Introns can also influence regulation and allow alternative splicing, adding to genetic complexity without contributing to the protein sequence themselves.