MadSci Network: Genetics
Query:

Re: Can multiple cell lineages produce multiple chromosomal banding patterns?

Date: Thu Jul 19 20:56:28 2007
Posted By: Alex Brands, Post-doc/Fellow, Biological ciences, Lehigh University
Area of science: Genetics
ID: 1183160984.Ge
Message:

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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