MadSci Network: Genetics |
Some viruses are able to splice their genome into the genome of the host. This obviously modifies the DNA of the host in that it introduces several new genes into the host genome. In this case, the infected cells will have slightly differing genomes than the uninfected cells. This is the only kind of infection that could be considered DNA modifying. It is extremely unlikely that the insertion of a viral genome would be visible in the chromosomal banding pattern, because it (the viral genome) is simply too small. You can see human chromosome banding patterns here, as photomicrographs and schematically: http://www.biology.ucsd.edu/classes/bimm110.SP07/lectures_WEB/L08.05_Cytogenetics.htm There are 3 billion bases in the human genome. The highest resolution chromosomal banding analysis can resolve around 800 bands total. That is an average of over 3 million bases per band. Viral genomes are usually on the order of tens of thousands of bases, if not smaller, with only a handful of genes. In a hypothetical example, if a viral genome of 30,000 bases inserted into a band of 3,000,000 bases, it would increase the size of that band by 1%, an increase much too subtle to see. Using a technique called FISH (Fluorescence In Situ Hybridization), a researcher can make a given segment of chromosome give off light, or fluoresce. This allows the detection of much smaller segments of DNA. Imagine trying to see a match against a sheet of wood from 100 yards away. It would be impossible. That's what it would be like trying to detect a viral genome insertion by looking at the banding pattern. Now imagine trying to see a lit match in the dark from 100 yards away. No problem! That's what detecting the viral genome with FISH would be like. So in the example you asked about, FISH could show different cell lineages, one uninfected, and the other infected. There is a nice explanation of FISH here: http://www.genome.gov/10000206 Alex Brands Lehigh University
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