Biology – 1.2 Concept and uses of classification systems | e-Consult

Organisms that share a more recent common ancestor are considered more closely related. This relationship can be demonstrated by comparing their DNA, specifically their base sequences. DNA is the molecule that carries the genetic information in all living organisms. The sequence of bases (Adenine, Guanine, Cytosine, and Thymine - A, G, C, and T) within DNA is like a genetic code.

Over time, as organisms evolve, mutations occur – these are changes in the DNA sequence. The longer the time that has passed since two species shared a common ancestor, the more opportunities there are for mutations to accumulate in their DNA. Therefore, species with a more recent common ancestor will have fewer accumulated mutations and thus more similar base sequences in their DNA compared to species with a more distant common ancestor.

The fewer differences in the base sequence, the more closely related the organisms are. A greater number of differences indicates a longer period of independent evolution and therefore a more distant relationship. This principle is fundamental to constructing phylogenetic trees, which illustrate evolutionary relationships.