I urge you to get the book, buy it in paper or in the e-book format:
Comparative Mammalian Cytogenetics : An International Conference at Dartmouth Medical School Hanover, New Hampshire, July 29–August 2, 1968
Kurt Bernischke | 6 décembre 2012 |Springer Science & Business Media
What I copied was from a free pre-view, you can browse it yourself.
It was pages 280 to 283, an article by Charles F. Nadler.
The last words need to be cited again : the best method of establishing fission is phylogenetics. In full:
Perhaps analysis of large samples from mammalian species whose normal karyotype is known in detail will provide cytological proof of fission by demonstrating two acrocentrics derived from a metacentric. Until that time, careful correlation of chromosomal patterns with phylogenies based on other kinds of taxonomic evidence offers the best means for establishing the fission hypothesis.
You do not get field observations confirming that the fission process occurs in mammals.
That is why I gave a diagram, since it was suggested to me that cross over of unequal portions could create an extra chromosome coexisting with the normal one from the other parent.
Or coexisting with the other portion?
But, so far, I have got no confirmation I was wrong, and can therefore still hope I was right :
- fission does not occur (as with tetraploidy, as with trisomy extended to tetrasomy divided into new pair), and therefore mammals cannot have a common ancestor with a lower karyogram than that of the mammal having the highest.
- And on the other hand, mammals have such a typical range of karyograms in 48 to 56 chromosomes, that the original mammal, if there was one ancestral to the rest, cannot have had more than 56 chromosomes either.
- And, there are mammals having more than 56 chromosomes, which therefore cannot descend from a proto-mammal.
But, how about trying to get around this by proposing a realistic, if perhaps not yet observed, scenario, from my previous diagrams?
Come on, some evolutionist taking up the challenge?
Hans Georg Lundahl