Why are there 23 pairs of chromosomes?

Jared Roach roach at u.washington.edu
Fri Jul 14 19:55:33 EST 1995


	I thought I might add a couple comments.

1) The evidence is overwhelming that there have been several independent
tetraploidizations during vertebrate evolution.  Most of the interesting
papers (with the hardest data) come from the Salmonid geneticists; look in
Medline for these.  Also, up my own alley, the vertebrate immune system
clearly arose in its present form following a tetraploidization.  It is
the simplest and perhaps only reasonable explanation for the parallel
genomic structure of the heavy and light immunoglobulin chain genes and
the alpha beta gamma and delta T-cell receptor genes.
	Thus not all tetraploidizations are lethal.  Why?  I dont' know.
Neither does anyone else.

2)  As mentioned before, there is little to no correlation between either
genome size or number of chromosomes with ANYTHING else.  Fish have as wide 
a distribution of genome size as any other vertebrate class.  This is probably
the strongest evidence that most junk DNA is indeed that.
	Why?  I don't know.  Neither does anyone else.



Good References

Fundamentals of Molecular Evolution
Li and Graur
an excellent primer on the subject for both the novice and expert

Molecular Evolution and the Immunoglobulin Superfamily
Hood and Hunkapiller
in "Evolution of Life" (Osawa and Honjo eds) 1991

Implications of the Diversity of the Immunoglobulin Gene Superfamily
Hunkapiller, Goverman, Koop, and Hood
CSH Symposia on Quantitative Biology  54:15-29    1989

Genome Size Evolution in Vertebrates: Trends and Constants
Olmo, Capriglione, and Odierna
Comp Biochem Phys   92B:447-453   1989
nice graphs

Variations in Genome Mass
Wachtel and Tiersch
Comp Biochem Phs   104B(2):207-213   1993






---------------------------------------------------
Jared Roach
225 Fluke Hall, Box 352145
Department of Molecular Biotechnology
University of Washington
Seattle, WA 98195
phone  685-7338
FAX    685-7301
roach at u.washington.edu



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