Comparing molecular sequences
Relationships between organisms can be investigated by comparing DNA base sequences or the amino acid sequences of equivalent proteins.
Sequences can be aligned so that corresponding positions are placed alongside one another. Matching positions and differences can then be identified or counted.
| Sequence | |
|---|---|
| Species A | ATGCCCGAT |
| Species B | ATGCCTGAT |
These DNA sequences differ at one base position. The same approach can be applied to longer DNA sequences or to amino acid sequences from the same protein.
Ways sequence data may be presented
- Aligned sequences allow individual matching and differing positions to be identified.
- Comparison tables may give the number of base or amino acid differences between pairs of organisms.
- Phylogenetic trees may summarise the relationships suggested by molecular comparisons.
Exam Tip: First identify whether the data show nucleotide bases or amino acids. Then compare equivalent positions and support your conclusion with the number or pattern of differences.