Аннотация:The review discussed problems of genome organization in the chromosomes of eukaryotes based on the data of genetical and molecular-biological studies. Particular attention is paid to the peculiarities of organization of genetic material in Drosophila. The main (euchromatic) part of the genome is considered as the totality of separate functional units (chromomere, gene loci), which have in the average a higher excess of DNA compared to the sized of the structural gene. The possible ways of internal organization of these units and the role of different types of DNA sequences in their function are discussed. The features of organization and function of the heterochromatic regions of chromosomes consisting of simple sequences of satellite DNA and tandemly repeated genes (polygenes), that code for general cellular functions (similar to the ribosomal genes) are considered. The instability of the number and even the sites of localization of polygenes in the chromosome, which can be determined by the peculiarities of their functions during differentiation of somatic cells is notes.