Introns are non-coding sections of a pre-mRNA transcript (and the DNA encoding it) that get spliced out before translation. In AP Bio, the fact that all eukaryotes have genes with introns is structural evidence for the common ancestry of eukaryotes (EK 7.7.A.1).
An intron is a stretch of a gene that ends up in the RNA transcript but never makes it into the final protein. When a eukaryotic gene is first transcribed, you get pre-mRNA that contains both exons (the coding parts) and introns (the non-coding parts). Before that RNA leaves the nucleus, the introns get cut out and the exons get stitched together in a process called splicing. So introns are the pieces that hit the editing room floor.
For AP Bio, the important thing isn't really the chemistry of splicing. It's that introns exist at all, and that they show up in eukaryotes across the board. EK 7.7.A.1 lists "genes that contain introns" as one of the shared features that points to all eukaryotes sharing a common ancestor. Bacteria and archaea mostly lack the kind of split genes that eukaryotes have, so this is a eukaryote-specific signature.
Introns live in Unit 7 (Natural Selection), specifically topic 7.7 Common Ancestry, and they back up learning objective AP Bio 7.7.A: describing structural and functional evidence for the common ancestry of all eukaryotes. Under EK 7.7.A.1, introns sit right alongside membrane-bound organelles and linear chromosomes as a shared eukaryotic trait. The big-picture theme here is Evolution. If a feature this specific shows up in fungi, plants, and animals alike, the simplest explanation is that they all inherited it from one ancestral eukaryote rather than each inventing it independently.
Keep studying AP Biology Unit 7
Exons and Splicing (Unit 6 / Unit 7)
Introns only make sense paired with exons. Exons are the coding regions kept in the final mRNA, introns are the non-coding regions cut out, and splicing is the cut-and-paste step that separates them. On the exam, conserved intron-exon boundaries are the evidence, so you need all three to tell the story.
Molecular Divergence (Unit 7)
Over evolutionary time, the actual sequences inside genes change. Exon sequences can diverge a lot while intron POSITIONS stay put. That contrast is the point: shared intron locations are a deep inherited feature even after the surrounding code has drifted apart.
Membrane-bound Organelles and Endosymbiosis (Unit 7)
Introns are one item on a checklist of eukaryote-only traits. Membrane-bound organelles like mitochondria and chloroplasts, linear chromosomes, and intron-containing genes together build the case in EK 7.7.A.1 that all eukaryotes share an ancestor.
You'll almost always meet introns in a common-ancestry context, not a molecular-biology-mechanism context. Classic MCQ stems compare a gene (actin, β-globin, hexokinase) across distantly related eukaryotes and report that the intron POSITIONS line up even when exon sequences have diverged. The expected answer is that conserved intron positions reflect inheritance from a shared common ancestor, not coincidence or convergence. What you have to DO is reason like an evolutionary biologist: shared features in many lineages point back to one ancestor. No released FRQ uses the term verbatim, but the same logic powers any free-response prompt that asks you to interpret molecular evidence for relatedness.
Easy to flip: introns are cut OUT and don't code for protein, exons stay IN and do code. A memory trick is exon = expressed, intron = interrupting/in-between. Both are in the original pre-mRNA, but only exons make it into the mature mRNA that gets translated.
Introns are non-coding parts of a gene that get spliced out of pre-mRNA before translation, while exons are the coding parts that stay in.
Under EK 7.7.A.1, the presence of intron-containing genes is structural evidence that all eukaryotes share a common ancestor.
Conserved intron POSITIONS across distant species, even when exon sequences have diverged, point to shared ancestry rather than coincidence.
Introns are a eukaryote signature, listed alongside membrane-bound organelles and linear chromosomes as shared eukaryotic features.
On the exam, the right move is to read conserved introns as inherited from a common ancestor, supporting learning objective AP Bio 7.7.A.
Introns are non-coding sections of a gene and its pre-mRNA transcript that are spliced out before the RNA is translated into protein. In AP Bio, they matter most as evidence (EK 7.7.A.1) that all eukaryotes share a common ancestor.
No. Introns are removed by splicing and never reach the ribosome, so they don't directly code for protein. The coding regions that stay in the mRNA are the exons.
Introns are cut out of pre-mRNA and are non-coding, while exons remain and are translated into protein. Remember: exon = expressed, intron = the interrupting in-between piece.
When you find introns in the same spots across fungi, plants, and animals, even though the exon sequences have changed a lot, the simplest explanation is that all those species inherited those intron positions from one ancestral eukaryote. Independent invention in each lineage would be far less likely.
Yes, in Unit 7 under topic 7.7 Common Ancestry. They show up in MCQs comparing genes like β-globin or actin across species, where you interpret conserved intron positions as evidence of shared ancestry.
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