What is the difference between constitutive and alternative splicing?

• A. Splicing only occurs in prokaryotes
• B. Constitutive splicing removes introns and joins exons in a single way
• C. Constitutive splicing removes introns and joins exons in a single way; alternative splicing yields multiple mRNA variants by including or excluding certain exons
• D. Alternative splicing yields multiple mRNA variants by including or excluding exons

Answer: (C)

Splicing can produce one or multiple mRNA products depending on how exons are joined. Constitutive splicing removes introns and joins all exons in a single, fixed arrangement, so only one mature mRNA is produced from the gene. Alternative splicing uses different patterns of exon inclusion or skipping, generating multiple mRNA variants from the same gene and often resulting in different protein isoforms. In many organisms, splicing is a eukaryotic feature because prokaryotes generally lack introns and the intron-removal process isn’t typical there.

This description fits best because it clearly states that constitutive splicing yields a single transcript, while alternative splicing creates multiple transcripts by including or excluding certain exons. The other statements only describe part of the picture or miss the contrasting idea.