On Tue, 13 Jun 1995 14:22:05 -0700 you wrote:
JM>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).
>
AC>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.
Not a very promising mechanism for macro-evolution. But then what is?
AC>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.
That is interesting. Does this indicate there is something unique
about human chromosomes? Is there any explanation for this?
AC>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.
Thanks for this info Art.
God bless.
Stephen