Eric Cabot (ecec at quads.uchicago.edu) wrote:
: In article <Pine.SUN.3.90.950821083818.2011A-100000 at possum>,
: Jim Cummins <cummins at POSSUM.MURDOCH.EDU.AU> wrote:
: [lots of good stuff deleted for brevity]
: >may well be historical examples of human-ape hybrids (we differ from
: >Chimpanzees by only a fraction of our genome) but such hybrids would
: >almost certainly be sterile through chromosomal imbalance.
: While chromosomal inbalance may well be the basis of the hybrid sterility
: among primates, that is certainly not always the case.
: In Drosophila - that other "crown of creation" - interspecific hybrid
: sterility is caused by geneic interaction. (References supplied
: on request). I wonder if chromosomal imbalance is even
: generally the cause of incompatibility between some closely
: related mammalian species.
I suppose we need to separate the role of chromosomal variation (nay,
..imbalance) as cause or effect. On the one hand chromosomal changes may
trigger divergence between, say, populations of the same species, and
hence precipitate a speciation event via a hybrid sink,(i.e. the effect
of the imbalance is to lead to speciation). On the other hand, these
imbalances may be manifest in different populations of a species as distinct
cytotypes, some exhibiting tandem fusions and others not, say. The mere
occurence of these differences does not necessarily CAUSE chromosomally
mediated speciation. In the final analysis, all living organisms should be
traceable to one common ancestor, phylogenetically speaking, therefore we
need also discuss the concept of hybridization in its relative sense: i.e.
in the context of consanguinity coefficients, and not as an absolute notion.