THE INFLUENCE OF GENOME SIZE ON THE POLYMORPHISM OF NON-SPECIFIC ESTERASES AND RAPD MARKERS IN BREAM ABRAMIS BRAMA L. AND ROACH RUTILUS RUTILUS L.

The genome size of the bream Abramis brama (L., 1758) is 1.3 times larger than that of the roach Rutilus rutilus (L., 1758), indicating a larger volume and diversity of noncoding DNA available for selection, which may be a source of latent genetic variability facilitating better co-adaptation of heterogeneous genomes during distant hybridization between these species. The evolutionary significance of genome size remains unclear. Analysis of random multilocus polymorphism (RAPD) markers and non-specific esterases was performed in A. brama and R. rutilus to identify the relationship with genome size. These markers cover both coding and non-coding regions of DNA, allowing analysis of the genome as a whole. The total number of loci identified for two RAPD primers in individual spectra of roach and bream was 89, of which 10 were common, and 18 (in roach) and 33 (in bream) were species-specific monomorphic. Both samples were highly polymorphic and differed significantly; the bream sample was more homogeneous. The spectra of non-specific esterases of the liver and skeletal/cardiac muscles of roach and bream were heterogeneous with coinciding electrophoretic mobility of the zones. The main Est-2 zone with the absence of tissue specificity in both species is a product of an independent locus and is represented by three allelic variants in roach (six genotypes were identified) and one component with high activity in bream. Polymorphism of this zone in bream is manifested by its division into two components with a low frequency of genotype occurrence (0.06), which may be a consequence of a mutation that has no adaptive value. The Est-1 zone of bream is tissue-specific, in the liver there is one component with high activity, in the heart - three with a predominance of homozygotes, in the serum - two fragments with weak activity and not in all individuals. In roach, the Est-1 zone of the liver is represented by two fractions with high activity, three components were identified in the heart, and the Est-3 zone has four allelic variants (nine genotypes). Thus, with an increase in the genome size of bream compared to roach, a decrease in the allelic diversity of esterase loci and a greater similarity of individuals to each other is shown, which may indicate a low variability of the structural genes encoding this protein, and a difference in the regulatory systems of the parental genomes.