Heterochromatin: The Visible with Many Invisible Effects

Heterochromatin represents a large fraction of eukaryotic genomes and is characterized by a high density of sequence repeats that remain condensed through the cell cycle. Based on our limited knowledge, we still suspect that chromosomal heterochromatin regions (HRs) in the genome of higher eukaryotes probably have no functions in the traditional in biology sense, and are possibly maintained by natural selection in the genome only owing to a number of important effects they have on the organism. But unlike other known forms of variability (biochemical, immunological, anthropogenetic, morpho-physiological, etc.), chromosomal HRs have no phenotypic manifestations. By studying chromosomal HRs variability in the human populations permanently living in various climatic-andgeographic conditions of Eurasia and Africa, in norm and pathology we have obtained the data indicating possible participation of chromosomal HRs in cell thermoregulation. Here we give some examples of possible cell thermoregulation participation in some stages of evolution and development.