Resources | Subject Notes | Biology
Classification systems are used by biologists to organize and categorize the vast diversity of living organisms. Traditionally, classification was based on observable physical characteristics. However, modern classification increasingly relies on genetic information, particularly the sequences of bases in DNA. This method provides a more accurate and objective way to determine evolutionary relationships.
The sequences of bases in DNA (Adenine, Guanine, Cytosine, and Thymine - A, G, C, and T) are like a genetic code. These sequences are largely inherited from parents and can be compared between different organisms. The more similar the DNA sequences, the more closely related the organisms are likely to be. This is because organisms that are more closely related share a more recent common ancestor.
Scientists compare the DNA sequences of different organisms to determine their evolutionary relationships. They look for patterns of similarity and difference. The more differences there are, the longer ago the organisms diverged from a common ancestor. These comparisons are used to construct phylogenetic trees, which visually represent the evolutionary history of life.
Consider comparing the DNA sequences of humans and chimpanzees. Humans and chimpanzees share a very high percentage of DNA sequence similarity (around 98%). This strong similarity indicates that humans and chimpanzees share a relatively recent common ancestor. This is a key piece of evidence supporting the evolutionary relationship between these two species.
| Characteristic | Traditional Classification | Modern Classification (DNA-based) |
|---|---|---|
| Physical Appearance | Size, shape, color, etc. | DNA sequence similarity |
| Behavior | Habits, social structures | DNA sequence similarity |
| Anatomy | Bone structure, organ arrangement | DNA sequence similarity |
| Evolutionary Relationships | Based on physical similarities | Based on genetic relatedness (DNA sequences) |
In summary, the analysis of DNA sequences provides a powerful and objective method for classifying organisms based on their evolutionary history. This approach has revolutionized our understanding of the relationships between all living things.