Research
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.
Is it Possible Artificial Sex Regulation in Mammals?
In spite of, impressive breakthrough in modern genetics and molecular biology the problem of artificial sex regulation of mammals still remains unsolved. Moreover, the very problem of sex origin of eukaryotes in the process of evolution still has not settled. Existing theories and hypothesizes mainly concern the maintenance and biological reasonability of sexual mode of replication. Their theoretic foundation is based on Darwin’s and Mendel’s ideas that sex was originated due to natural selection and genes. On the basis of other model of genesis and sex evolution of eukaryote, it was suggested the idea of artificial sex regulation of mammals. Seemingly, the sex differentiation (SD) in animals and human is determined by the amount of constitutive heterochromatin region (cHR) in the Y chromosomes of the undifferentiated embryonic gonads (UEG) via cell thermoregulation. It is assumed the medulla and cortex tissue cells in the UEG differ in vulnerability to the increase of the intracellular temperature because of their anatomical position in genital ridges. If the amount of the cHR on Y chromosome is enough for efficient elimination of redundant metabolic heat from rapidly growing UEG cells the medulla tissue survives. Otherwise it doomed to degeneration and a cortex tissue will remain in the UEG. For artificial regulation of the SD it is proposed to remove a layer of cortex in the UEG.
On The Origin of Sex
The problem of sex origin of eukaryotes in the process of evolution still has not settled. Existing theories and hypothesizes mainly concern the maintenance and biological reasonability of sexual mode of replication. Their theoretic foundation is based on Darwin’s and Mendel’s ideas that sex was originated due to natural selection and genes. Another model is proposed – sex of eukaryotes was originated as a result of long-term evolution of non-coding DNAs in a genome at one of the branches of prokaryotes. Non-coding DNAs accumulation and evolution in prokaryotes’ ring chromosomes eventually led to emergence of mitotic chromosomes and mitotic way of cell division. Sex and sexual replication became possible since that time when modified variant of mitosis – meiosis – have originated. Separate stages of the proposed model may be exposed to experimental check.
