RNA Splicing Process in Eukaryotes

Steps:

• Transcription produces pre-mRNA with both coding and non-coding regions.
• Non-coding sequences (introns) are removed during splicing.
• Coding sequences are joined to form mature mRNA.
• These coding sequences are known as exons.

Why A is correct:

• Exons are the coding sequences in eukaryotic genes that are retained and joined to form the final mRNA, as defined in molecular biology.

Why the others are wrong:

• B. Codons are triplets of nucleotides within exons that specify amino acids, not the sequences themselves.
• C. Introns are the non-coding sequences removed during splicing.
• D. Primary transcripts refer to the initial, unprocessed RNA before modification.

Final answer: A