Re: [RML] News Flash - DNA

peter.unmack at ASU.Edu
Sun, 26 Apr 1998 23:12:39 -0700 (MST)

On Fri, 24 Apr 1998, Mach T. Fukada wrote:

> Ah but you could use the arbitrary primer method to create a "genetic
> finger print" and using the same set of primers with closely related
> organisms look for conserved regions of dna for sequenceing and further

If you are referring to the technique called genetic finger printing then
this method is not suited to looking at species differences. Finger
printing is good for distinguishing populations and even individuals (I
think this is what they used in OJ's case). Finger printing, as my
limited understanding has it, is something like this. Along the strands
of DNA you get repeats of the same nucleotide (of which there are four
that make up the genetic code, each occurs only in pairs across the two
complimentary DNA strands, A-T and C-G) such as AAAACGTATGTC (considering
only one of the two complimentary DNA strands). What the DNA splicing
enzyme does is cut the DNA every time it hits a AAAA sequence (with it's
complimentary TTTT). Then you
run all this on a gell and you get different bands for the differing
lengths of DNA (smaller pieces travel quicker/further I think). This is
what the finger print is. You are not looking directly at the DNA, ie
sequencing, hence you really don't know much about what you are looking at
(ie, does it have any biological meaning?). Different enzymes will cut it
at different sites with differing numbers of repeats. This type of
variation in repeat sequences tend to be common as they tend to be sites
of higher mutation rates, hence variability is higher. If a particular
area of DNA is too variable then it is next to useless for distinguishing
species, but very good for pops or individuals.

> Alternatively, for certain groups we know that
> there are highly conserved DNA sequences, that the region between these
> points could be amplified or the conserved region could be amplified via
> PCR and sequenced to look for small changes in these conserved region.

This type of work is more typical of what one would use to look at
species level differences. As you mention, some regions tend to be more
conservative (some are even identical across all vertebrates!). Hence,
this conservative regions are less likely to vary with species, but more
likely to vary amoung species, hence being good for distinguishing them.

Tootles

Peter J Unmack peter.unmack at asu.edu
---------------------------------------------------------------
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