Sequence Data
- Sequence data can be obtained from:
- DNA
- The base sequence of DNA found in the nucleus, mitochondria and chloroplasts of cells can be determined
- RNA
- RNA is the product of transcription, and the RNA base sequence provides information about the DNA base sequences of genes that are expressed in a cell
- Proteins
- The amino acid sequence of expressed proteins can be determined
- DNA
- Similarities between sequence data in different species suggest that all species share a common ancestor
- The sequences for comparison must come from the same part of the DNA, and are often taken from regions of DNA that are highly conserved, meaning that they have changed very little over time; this is important for several reasons:
- Like needs to be compared with like; comparing two completely different regions of DNA will not yield useful information
- There are likely to be relatively few differences, so similarities and differences can be easily identified
- Conserved sequences are also more likely to exist in a wide range of species
- Examples of conserved sequences are those that code for essential proteins, e.g. haemoglobin, or enzymes involved in respiration
Comparing DNA sequences
- DNA is extracted from cells
- DNA can be extracted from blood or skin samples from living organisms or from fossilised remains
- The extracted DNA is processed, analysed and the base sequence is obtained
- The base sequence is compared to that of other organisms to determine evolutionary relationship
- The more similarities there are in the DNA base sequence, the more closely related members of different species are
- E.g. in 2005 the chimpanzee genome was sequenced, and when compared to the human genome it was discovered that humans and chimpanzees share almost 99% of their DNA sequences, making them our closest living relatives
- Data from multiple sources, e.g. several different genes, are compared to increase the level of certainty
- The data gained from comparing sequence data can be used to build an evolutionary tree
Comparing DNA sequences diagram
Similarities and differences between the DNA of two species provide information about their divergence from a common ancestor