[Evolutionary chromosomes and sex dimorphism]

In order to understand the phenomenon of sex, it is not enough to know about its reproductive role and role in recombination. In addition, knowledge of its evolutionary role is required. Sexual differentiation allows us to test evolutionary innovations in the male genome before they are transmitted to the female genome. This is possible in the framework of dichronous evolution, when the evolution of the male sex goes faster than the evolution of the female sex. This implies that there clearly should be male genes, which are already present in the male genome, but are not yet in the female genome; and vice versa, there should exist female genes, which have already been lost by the male sex, but still remain in females. Dichronicity results from different reaction norm of the sexes. This interpretation implies (1) the nomadic behavior of genes in the genome (2) the existence of evolutionary sexual dimorphism, which begins in the form of modificational changes in the female sex followed by selection-derived changes in the male sex; (3) the discovery of evolutionary roles of chromosomes and the proposition of a new concept, according to which the Y-chromosome represents a "gateway" for environment-related information coming to the genome, i.e., place of "birth" and testing of new genes, which comprise the basis of evolutionary sexual dimorphism--its initiator, accelerator, and regulator. The X-chromosome is the "transport" chromosome that transfers new genes from the Y-chromosomes into autosomes and therefore serves as a stabilizer, relaxer, and liquidator of evolutionary sexual dimorphism; it also serves as repository of the outgoing genes that await elimination. This concept provides for a new interpretation of the appearance, localization, and movement of genes along chromosomes and between them, and it sheds new light on the phenomena of chromosomal inactivation, mobile genes, association of Y-chromosome with stress, viruses, etc.