A DNA sequence is the precise order of nucleotides (A, T, C, G) in a DNA molecule. In AP Bio Unit 7, comparing DNA sequences across species is biochemical evidence for evolution and common ancestry: the fewer the differences, the more closely related two organisms are.
A DNA sequence is just the order of nucleotides, the A, T, C, and G bases, along a strand of DNA. That order is the genetic information that codes for proteins, so two organisms that share a recent common ancestor will have very similar sequences for the same gene.
In AP Bio, DNA sequences show up most directly in Topic 7.6, Evidence of Evolution. Per EK 7.6.B.2, comparing DNA nucleotide sequences (and the protein amino acid sequences they code for) gives evidence for evolution and common ancestry. The logic is simple: mutations accumulate over time, so the more differences you find between two species' sequences for the same gene, the longer ago they split from their shared ancestor. Fewer differences means closer relatives.
This term lives in Unit 7: Natural Selection, specifically Topic 7.6. It supports learning objective AP Bio 7.6.A (describe the types of data that provide evidence for evolution) and AP Bio 7.6.B (explain how biochemical and other data show organisms changed over time). DNA sequence comparison is the biochemical leg of the evidence-for-evolution stool, sitting alongside morphological homologies and fossil data described in EK 7.6.B.1. The big idea is that evidence from many independent disciplines, including biochemical data, all points to the same evolutionary story (EK 7.6.A.1).
Keep studying AP Biology Unit 7
Nucleotide (Unit 1)
A DNA sequence is literally a chain of nucleotides in a specific order. You learn what a single nucleotide is back in Unit 1, then in Unit 7 you zoom out and use the whole sequence as a molecular record of evolutionary history.
Gene (Units 6-7)
A gene is a stretch of DNA sequence that codes for a product. When you compare DNA across species in Topic 7.6, you compare the same homologous gene in each one, so understanding what a gene is makes the comparison make sense.
Fossil Evidence (Unit 7)
Fossils and DNA sequences are two different evidence types pointing to the same conclusion. Fossils give you the timeline and morphology from extinct organisms; DNA gives you molecular relatedness among living ones. EK 7.6.A.1 wants you to see how these independent data sources agree.
Genome (Unit 7)
A genome is the complete set of an organism's DNA sequences. Practice questions often compare genomes across species, like measuring percent differences in homologous sequences to rank how related five vertebrates are.
Expect DNA sequences in both multiple-choice and free-response questions about evidence for evolution. A classic MCQ gives you percent differences in homologous DNA sequences between several species and asks you to infer which pair is most closely related (the smallest percent difference) or to build/interpret a phylogenetic tree, often assuming a constant mutation rate as a molecular clock. Some questions go deeper and distinguish synonymous substitutions (no amino acid change) from nonsynonymous ones (amino acid change) to reason about selection. On the 2018 Long FRQ Q1, a phylogenetic tree built from mitochondrial DNA sequence comparisons framed questions about how bear populations are related. What you need to DO: read the data, conclude that fewer sequence differences means closer common ancestry, and connect that to the broader claim that multiple independent lines of evidence support evolution.
Both are biochemical evidence under EK 7.6.B.2, but they're not the same molecule. A DNA sequence is the order of nucleotides (A, T, C, G); a protein sequence is the order of amino acids that the DNA codes for. DNA changes can be silent (synonymous) and not alter the protein, so DNA sequences often show more differences than the proteins they encode. Both can be compared across species to support common ancestry.
A DNA sequence is the order of nucleotides (A, T, C, G) in a DNA molecule, and that order carries genetic information.
Per EK 7.6.B.2, comparing DNA sequences across species is biochemical evidence for evolution and common ancestry.
Fewer differences between two species' homologous sequences means a more recent common ancestor, so they are more closely related.
DNA sequence data is one of several independent evidence types (alongside fossil, morphological, and geological data) that all support evolution under EK 7.6.A.1.
On the exam you often use percent sequence difference and a constant mutation rate to build or read phylogenetic trees, as in the 2018 Long FRQ using mitochondrial DNA.
It's the precise order of nucleotides (A, T, C, G) along a DNA molecule. In AP Bio Unit 7, comparing DNA sequences between species is biochemical evidence for evolution and common ancestry.
Yes. Mutations build up over time, so two species with fewer differences in the same homologous DNA sequence shared a common ancestor more recently. That's exactly the reasoning behind the percent-difference MCQs in Topic 7.6.
Both are biochemical evidence under EK 7.6.B.2, but a DNA sequence is nucleotides while a protein sequence is amino acids. Because some DNA changes are synonymous and don't change the protein, DNA sequences often show more differences than the proteins they code for.
No. EK 7.6.A.1 lists evidence from many disciplines, including geographical, geological, physical, biochemical, and mathematical data, and EK 7.6.B.1 adds fossils and morphological homologies. DNA sequence comparison is the molecular piece that agrees with all of them.
They usually appear as data you have to interpret, like the 2018 Long FRQ where a phylogenetic tree of bear populations was built from mitochondrial DNA sequence comparisons. You read the relatedness off the data and explain what it tells you about common ancestry.