1. DNA as a blueprint:
* DNA contains the genetic code that dictates the production of proteins. These proteins are responsible for a vast array of functions within an organism.
* The sequence of DNA nucleotides (A, T, C, G) determines the sequence of amino acids in a protein.
2. Mutations and Evolutionary Change:
* Over time, random mutations occur in DNA sequences. These mutations can be neutral, beneficial, or harmful.
* Neutral mutations accumulate over generations. The more time that has passed since two species shared a common ancestor, the more differences they will accumulate in their DNA sequences.
* Beneficial mutations can help a species adapt to its environment, leading to evolutionary change and the creation of new species.
3. Comparing DNA and Amino Acid Sequences:
* Scientists can compare the DNA sequences of different species to identify similarities and differences.
* They can also compare the amino acid sequences of proteins, which are directly encoded by DNA.
* The more similar the DNA or amino acid sequences are between two species, the more closely related they are.
4. Molecular Clocks:
* Scientists have developed "molecular clocks" based on the rate of mutation in certain genes.
* These clocks can be used to estimate how long ago two species diverged from a common ancestor, based on the number of differences in their DNA or protein sequences.
Examples:
* Humans and chimpanzees: Share about 98.8% of their DNA sequences. This close similarity suggests a recent common ancestor.
* Humans and bacteria: Have much more different DNA sequences, reflecting their distant evolutionary relationship.
Key Points:
* Differences in DNA and amino acid sequences are a direct reflection of evolutionary history.
* The more differences, the longer ago two species diverged.
* Molecular clocks allow scientists to estimate divergence times.
By comparing DNA and amino acid sequences, scientists can gain valuable insights into the evolutionary relationships between species and construct phylogenetic trees, which represent the evolutionary history of life on Earth.
