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4.2. Why gene/protein sequences may be similar?
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Before measuring the similaritybetween the sequences, it's interesting to answer the question: why gene or protein sequences may be similar? It is indeed veryinteresting because the answer is related to the theory ofevolution which is due, as you all know, to Darwin. What Darwinsays is that species evolve in time and there is a creation ofnew species for existing ones. So there is an evolutionof species over time. He was a very thinking man, huh. This evolution can be also seenon the genomic sequences. Let's see this very small and partialtree of life and hypothetical tree of life. Here you have thespecies and you have this phenomenon of speciation giving to two different species and again different species and so on and so on. On the genomic level each of thesespecies of course has genomes, genes and DNA sequences, let'stake this gene here of these ancestral species as one. The species evolve in time and ofcourse the genomes evolve in time. They are on the DNA modificationthat is what we call mutation so that sequences evolve over time.
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