Chromosome is a relatively stable genetic entity, yet different species,
even sister species, could differ much in the haploid number. It would
be interesting to study how some chromosomes get lost and some remain
during speciation, or to study why some chromosomes get bigger and some
get smaller during evolution. To do this we need to know which chromosome
from one species (say mouse) is analogous to which chromosome from another
species (say human).
It would be nice if the number 1 chromosome of the mouse is analogous to
the number chromosome of the human, which is in turn analogous to the
number 1 chromosome of the dog, or pig. It would be even nicer if we
could trace to the past and learn which chromosome was split into two
300 million years ago and which two chromosomes merged into one 3
millions years ago, etc.
It is perhaps true that the X chromosome in human and that in mouse are from
the same ancestral X chromosome, and the same is perhaps also true for
the Y chromosome. For the rest of the chromosomes, it would be much
more difficult to identify which one from mouse and which one from human
have evolved from a common ancestral chromosome. It would be nice to have
a method to quickly do the identification so that eventually the numbering
of chromosomes will be modified to reflect some phylogenetic relationship.
I hope that someone will write a book entitled "Evolution and Phylogeny of
Chromosomes".
Xuhua Xia
