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By comparing corresponding gene sequences from three or more organisms, we can deduce relationships which can be used for biological classification. Portions of a gene with the greatest number of differences (polymorphisms) generally produce the largest amount of useful data for classification of new specimens. In order to identify highly polymorphic regions, we displayed the 28S ribosomal RNA gene as a sequence logo.¹⁵ In this representation, the height of letters measures the degree of sequence conservation among several species. We then picked a region which has two conserved motifs surrounding a highly variable domain. The conserved portions are the same in many organisms, so we were able to use the polymerase chain reaction (PCR) technique to amplify the variable portion in the middle. When sequenced and compared, these amplified pieces of DNA will allow taxonomic classifications to be made.

The two patterns shown here represent two different views of a control switch in the genetic material of a virus called T7. Like many other viruses, T7 is made of proteins that coat and protect its genetic material DNA (deoxyribonucleic acid). The virus looks like a lunar-lander landing on the moon. When a T7 particle contacts the surface of the bacterium Escherichia coli, it sticks there. Once it has landed, it injects its DNA into the cell, much like a hypodermic needle does. The DNA contains instructions for taking over the bacterial cell. The cellular machinery unwittingly copies these instructions into RNA. The RNA is then used to make proteins that stop the normal cell mechanisms. Other instructions tell the cell to make copies of the viral DNA and to make the proteins of the viral coat. These are assembled to produce perhaps a hundred new T7 particles. The final instruction causes the cell to burst open, just as in the movie “Alien”…