Ancestors & DNA
Biology: Cambridge International GCSE Supplement, topic 1.2.3
Ancestors & DNA
DNA sequences are used to classify living things, with similar sequences showing a recent common ancestor and greater differences showing a distant ancestor.
What is DNA?
- DNA (Deoxyribonucleic acid) is the genetic material found in all living organisms.
- It is a long molecule made up of four bases:
- Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
- The sequence of these bases forms a unique code, like a set of instructions, for each living thing.
DNA and classification
- Scientists compare DNA base sequences to classify organisms.
- The more similar the base sequence, the more closely related the organisms are.
- This is because closely related organisms share a more recent common ancestor.
How DNA shows relationships
- Organisms with a recent common ancestor have very similar DNA.
- Organisms with a distant ancestor have more differences in their DNA sequences.
- Example:
- Humans and chimpanzees share a recent ancestor, so their DNA sequences are very similar.
- Humans and a type of bacteria share an ancient, distant ancestor, so their DNA sequences are very different.
Why DNA is useful in classification
- DNA is more accurate than just comparing physical features.
- It shows evolutionary relationships between species.
Test yourself on Ancestors & DNA
What is DNA made up of?
Why do humans and bacteria have very different DNA sequences?