Re: HIPS: HYB: chromosome counts

From: Linda Mann <lmann@icx.net>

Bill Shear wrote:
> It might be that the uneven numbers of chromosomes are due to observer
> error.  Usually chromosome counts should be verified by more than one
> observer, especially if they are considered anomalous or unusual.

Definitely!  

Way back when.. part of my first job after college was making slides of
fern spore nuclei (conveniently haploid) and making chromosome counts. 
Part of my second job was (ick) culturing snippets of live mouse ears
and making chromosome counts.  It's been so long ago, I can't really
remember the details (in both cases, I worked for someone who had to do
most of the thinking), except that the more chromosomes you have to
count, the harder it is to get a good count because they tend to stick
together and pile on top of each other to some extent.  Those nuclei are
get crowded.  
Part of what we did when making counts was draw what we were seeing thru
the microscope, so I assume that's standard technique.  With the ferns,
I was working for a taxonomist who was only interested in total number
(he was comparing morphological characteristics of diploid and polyploid
plants).  With the mice, we were looking for chromosomal abnormalities
resulting from radiation etc, so the actual shapes of each pair of
chromosome was important.  

Anyway, as I recall, the actual counting is not that big a deal, though
a time-consuming pain in the eyeballs.  And unless these folks only used
one cell to count, or if the chromosomes all look alike, which from what
Sharon says about the base number being 12 (4 sets of 48 would look
alike), it 'should' be a lot of work but 'easy' to get a good count. 
For the mouse work, two of us worked together and made random checks of
each others slides and drawings - never found anything questionable as I
recall.  

Linda Mann



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