At one point while we were going through a fairly basic DNA amplifying process, Blair mentioned something called tetranucleotide frequency biases, and I was intrigued enough to track down a paper about it. One of the first things that you learn in any Intro Bio class is that three nucleotides make a codon, which codes for a specific amino acid, and a sequence of amino acids is how you make a protein. For example, AUG is a start codon, and is required to start all amino acid sequences. Are my engineers still with me? (I tease). Years ago scientists figured out how to sequence DNA, and established which codons corresponded to which amino acids, and since then DNA sequencing has been used to establish relationships between different animal species and establish when evolution occurred.
Now, an entirely new relationship has been discovered, not in sequences of three nucleotides but in four. The paper that I’ve pulled most of this information from (Evolutionary Implications of Microbial Genome Tetranucleotide Frequency Biases – David T. Pride et al) was only published in February of this year, but it appears that the idea has been around since 2006 at least. There are significant biases in the order that 4 nucleotides occur in DNA sequences, to the point that researchers have been able to group microbes based on the relatedness of these frequencies. When researchers used tetranucleotide patterns to group 27 representative microbial species, the phylogenetic tree produced was very consistent with one produced using 16S rRNA (an accepted way of grouping microbes since it is a section of genetic material that conserved among species and not as variable as other sections of DNA). Similarities increased when only coding sections of DNA were sequenced and compared. There are hints that similar patterns may be found in sequences of only two nucleotides to many more.
What does this mean? To be perfectly honest, after only two papers I’m not sure about all the implications. It appears that we’ve found yet another relationship in patterns of DNA, and a new way to look into the relationships between species. It means there are still things to be discovered in the genetic material that makes us what we are, and that the sequencing done by the Human Genome Project is just the beginning.And it might all have happened because some scientist got a little sidetracked and wondered what would happen if you added one more nucleotide to the mix! I guess the lesson is to explore what catches your fancy, you never know when you’re going to revolutionize your field. With that, I’m back to studying. Good luck with your finals everyone!