Despite being up to several million DNA building blocks in size, centromeres can “jump” to other positions without causing the DNA to move. Consequently, in rare cases, a new centromere can arise as it has already occurred in a closely-related ape species.
From “Chromosome Centromeres Are Inherited Epigenetically” (ScienceDaily, Nov. 3, 2011), we learn:
Centromeres are specialised regions of the genome, which can be identified under the microscope as the primary constriction in X-shaped chromosomes. The cell skeleton, which distributes the chromosomes to the two daughter cells during cell division, attaches to the centromeres. In most organisms the position of the centromere is not determined by the DNA sequence. Scientists from the Max Planck Institute of Immunobiology and Epigenetics in Freiburg have succeeded in demonstrating that the position, function and inheritance of the centromere are determined by the histone CenH3, a DNA packaging protein.
In most organisms the position of the centromere is not determined by the sequence of the DNA building blocks, i.e. the DNA sequence, but epigenetically. The only exception to this rule is the unicellular fungus baker’s yeast, in which a specific DNA sequence “encodes” the position of the centromere.
The step from a DNA-identified centromere in baker’s yeast, in which the position “is set in stone,” to a protein-defined centromere position which is easier to change may also play a role in evolution. Despite being up to several million DNA building blocks in size, centromeres can “jump” to other positions without causing the DNA to move. Consequently, in rare cases, a new centromere can arise as it has already occurred in a closely-related ape species. Therefore neo-centromeres might contribute to the emergence of new species.
Wouldn’t the ghost of LaMarck be proud, after centuries of ridicule?,