Re: tetrapoidy in mammals
Arthur V. Chadwick (chadwicka@swau.edu)
Thu, 11 Nov 1999 09:34:28 -0800At 08:56 AM 11/11/1999 -0400, you wrote:
>Group,
>
>I couple of months ago there was a short communication in Nature that I
>meant to pass on. A tetrapoid rat species seems to have been found. The
>Red Viscacha rat has 102 chromosomes though only one X and Y. Other
>related genera of rats have 2N=57 so a strict doubling of them would have
>lead to 4N=114. It is postulated that some chromosomal material has been
>subsequently lost (another possibility is some extinct rat had 2N=51 that
>doubled). What boggles the mind is that polyploidy could even occur in
>mammals when one thinks about all the obstacles that have to be overcome to
>maintain some sence of normallacy for these animals. On top of that the
>Red Viscacha appears to uneffected at this point by carrying around twice
>the genetic material that most other mammals though its sperm heads are
>twice the size of other related rats. This is really an amazing example of
>something that seems virtually impossible but there it is.
make a contribution to the host are thrown out (though in human-animal
hybrids it is strange that it is always the human chromosomes that are
excluded). Perhaps over time the chromosomes that, when present in
duplicate were disadvantageous, were eliminated. In cases where an extra
copy conferred some advantage, it would be retained. Or it could be like
the Muntjac, where one species has 46 chromosomes, another nearly identical
species has 8 (9 in the male!), even though the two species are hardly
distinguishable. In this case the genetic material is the same in both
species, but the arrangements of the chromosomes are vastly different.
Art
http://geology.swau.edu