In a review article published in the August 10, 2001, issue of the journal Science, Henikoff and colleagues Kami Ahmad and Harmit S. Malik at the Fred Hutchinson Cancer Research Center theorize that the rapid evolution of centromeric DNA may provide a mechanism by which newly evolving species rapidly become genetically incompatible with one another.
Each chromosome possesses a centromere, which is the site at which sister chromatids are held together. During mitosis and meiosis, the chromatid pair separates, and the centromere is the point of attachment of spindle fibers that pull each chromosome to opposite poles of the dividing cell. "While the centromere is a locus on the chromosome, it is different than a gene, because it is a locus that is acted upon by the apparatus of cell division," said Henikoff.
And unlike genes, which are amenable to mapping and sequencing, probing the genetic makeup of the centromere has proved to be a dead end because of the centromeres unusual structure. "The centromere has remained enigmatic ever since it was discovered that centromeric DNA is highly repetitive," said Henikoff. "Current methodology really doesnt allow the sequencing of centromeric DNA. Thus, nobody has sequenced the centromeres of the human genome, the fly genome, or that of any other complex organism. They remain big black holes often millions of bases in length in every chromosome."
The wide variability of centromeric DNA across different species has led some researchers to dismiss its importance. According
Contact: Jim Keeley
Howard Hughes Medical Institute