Re: Polyploidy and how to get more DNA.

Arthur V. Chadwick (chadwicka@swac.edu)
Tue, 13 Jun 1995 14:22:05 -0700

>1. In evolutionary theory is polyploidy seriously considered as a
>mechanism for increasing base chromosome numbers. It struck me
>that it is about the only mechanism I know of that would increase
>the number of chromosomes (other than the case of sexual
>reproduction of diploid gametes - which is not that common). I
>don't think you can as easily add to the DNA in a chromosome as
>you can in a prokaryotic (bacteria).

A couple of points of interest:

In humans and mammals in general the presence of polyploidy in even one
chromosome is almost always incompatible with life ..exception is Down's
Syndrome, triploidy in chromosome 21, and the sex chromosomes which are for
understandable reasons more readily dealt with in extra copies. Not very
desireable conditions in any case.

If human and any other cell type are fused to form a hybrid cell containing
chromosomes of both cell types, as the resulting hybrid cell is cultured in
many passages, it will gradually and selectively expel all HUMAN
chromosomes, while retaining the chromosomes of the other species,
regardless of what the species may be. Aside from any other interest this
may have, it is an exceedingly valuable tool for cell biologists who can
selectively clone one human chromosome by fusing a human cell with a cell
from another species deficient in some factor required for growth. The
human chromosome containing the equivalent gene will then remain, supplying
the deficiency. The resulting clone of cells containing only one human
chromosome is called a "panel", and its usefulness in mapping specific genes
to specific human chromosomes is apparent. Thus chromosomes that are not
performing a function will be lost.

As for polyploidy as a mechanism for evolution, it does not result in new
information, but just in additional gene product. This is generally not
beneficial to the organism for survival unless it is artificially selected
for, since wheat, corn, etc. quickly revert to the wild type when not
cultivated.


Art