On 5 Sep 1996, Jun-Zhi Wei wrote:
> Could anyone tell me the actual sizes (how many microns) of double minute
> chromosomes, the largest and the smallest chromosomes in metaphase human
> and mouse cells? Thank you.
> J.-Z. Wei
This is not really an easy question... length (in microns) depends on the
stage of contraction of the chromosomes. For instance, there is roughly a
20:1 reduction in apparent length between prophase chromosomes and the
same chromosomes after an overnight colchicine incubation (they'll look
like little cubes instead of rods). This is not a change in the length of
the DNA per se, just a change in packing.
Overall, mouse chromosomes are "shorter" than human, I'd guess (from
memory here) the longest mouse chromosome to be about 1/3 the length of
the longest human chromosome, at roughly the same level of condensation.
But again, there is no "standard" to measure them against.
DMs (double minutes) can also vary quite a bit in size, from dust-like to
chunky little mini-chromosomes. Even within a single cell line/tumor.
Hope this is some help...
The Johns Hopkins Hospital
Baltimore, Maryland, USA