Development needs a clock: the same genome must express different programs at different times, in a fixed order, in every individual. In Cognimed that clock is chromosomal.
The mechanism. Every cell division shortens the telomere. Telomere length sets the level of TERRA, the RNA transcribed from the telomere itself, and TERRA in turn regulates the Polycomb repressive complex PRC2 (see the Polycomb Complex). So the chain telomere → TERRA → PRC2 converts a division count into a repression level: as the count rises, Polycomb repression is progressively withdrawn.
What it reads. The zygote carries an inherited program — a layered methylation record laid down over evolutionary time, with embryonic, fetal and adult strata. PRC2 reads this record in reverse developmental order: the fates that must appear first are released first. The same clock drives HOX colinearity — the ordered anterior-to-posterior activation of the HOX clusters is its positional signature.
The evidence. The mechanism clock reproduces the measured order of cell-fate appearance in the zebrafish atlas (Spearman 0.95) and the anterior–posterior neural split (AUC 0.86); an independent, measured clock built from the ENCODE mouse fetal enhancer-opening atlas times 38 cell types across 11 organs, with progenitors opening before their differentiated descendants in the organs where bulk tissue permits the comparison.
One clock, two hands: the division head drives it, the differentiation head is gated by it. It is also the model’s natural handle on aging — partial epigenetic reprogramming is, in these terms, a controlled rewind. See the papers, especially Papers 1, 6 and 8.