The environment controls the DNA
The DNA coils itself around protein complexes called nucleosomes. Importantly, nucleosomes can carry various chemical modifications that either allow, or prevent, the expression of the DNA wrapped around them. Every time a cell divides into new cells, its double-stranded DNA splits into two single strands, which then each produce a new double-strand.
Nucleosomes though are not duplicated like the DNA-strands. Rather, they are distributed between the two new DNA double strands and the empty spaces are filled by new nucleosomes. Cell division is therefore an opportunity for changes in the nucleosomal composition of a specific DNA region. Changes can also happen during the lifetime of a cell due to chemical reactions allowing interconversions between the different nucleosome types. The effect of these changes can be that a latent capacity that was dormant comes to life, or, conversely, that a previously active capacity shuts down.
Same inheritance ?different traits
In the practical experiment molecular biologists used a mutant of a yeast cell which was bi-stable, in that it could become either of a single sex or hermaphrodite. The experiment showed that a spontaneous change occurred in the yeast cells about every 2000 cell-generations. By building a mathematical model based on positive feedback from the microscopic state of the nucleosomes, the research group could simulate the experimental results and in this way gained insight into the mechanisms by which living cells with identical DNA can achieve extreme differentiation.
The research at the ‘Models of Life?Basic Research Center at the Niels Bohr Institute has shown that communication between nucleosomes and positive feedback are likely to constitute fundamental memory mechanisms in individual cells. The mechanism gives
Source:University of Copenhagen