"Raphanus" wrote in message
ups.com...
While Homo sapiens usually have 46 chromosomes there are individuals
with 45 chromosomes (Turner's syndrome), 47 chromosomes (Down,
Klinefelter's, XYY and XXY syndromes) and even 48 chromosomes (XXYY
syndrome). Most of these variants are fertile and able - with
individuals with the "normal" complement of 46 chromosomes - to produce
children.

These above are cases with an extra one [or a shortage of one] of the
usual set chromosomes; the term is "trisomy". There have also been
human examples where two of the usual chomosome complement have
essentially fused to become one, or one has split to become two.

http://groups.google.com/group/talk....3decba44c19721

These latter types of changes are more relevant to the chromosomal
changes seen in evolving lineages than trisomies. A fusion of two
ancestral chromosomes that are still separate in the other great apes
is recognized to have occurred within the human lineage at some point
since our last common ancestor with chimpanzees.

http://www.gate.net/~rwms/hum_ape_chrom.html

Are there other species also with a variant chromosome count? Or do we
know? Homo sapiens is, no doubt, the species we know most about and
maybe such variation has eluded detection in other species?

There are different kinds of chromosome changes and chromosomal
variants, and they are well known in many species, including plants
and animals. There are numerous species known with chromosomal
polymorphisms and two or a whole range of different chromosome
numbers known within a single biological species.

http://groups.google.com/group/talk....98937b7a3161fb
http://groups.google.com/group/talk....c6e6cf5b4c9ceb
http://groups.google.com/group/talk....7bb981b4a5e2ac
http://groups.google.com/group/talk....ef84ad8e77ed77

Individuals "heterozygous" for different chromosomal configurations
may still be highly fertile, if two chromosomes of one set can still
pair up at meiosis with the corresponding one chromosome of the other
set.

Yet another form of chromosomal change that is especially important
in plants is polyploidy, where whole sets of ancestral chromosomes
are duplicated. It is one form of rapid new-species formation.
Many examples are well-known. Often, a new polyploid species was
derived from a hybrid between two ancestral species; the term for
this is "allopolyploidy".

cheers