Abstract: The review is focused on the development of ideas about the role of one of the most mysterious phenomena of developmental biology, i.e., the transformation of chromosomes into the so-called lampbrush chromosomes (LBCs). Eukaryotic chromosomes in the LBC phase are characterized by a low level of condensation and discrete structure formed by numerous linearly arranged compact chromomeres, from which lateral loops coated with transcripts are extruded. Linear sizes of LBCs exceed the sizes of the corresponding mitotic chromosomes by more than 30 times, making LBCs a valuable model for analyzing the structure and functioning of chromosomes, as well as structural and functional organization of the genome as a whole by the methods of molecular cytogenetics and genomics with very high resolution. Wide distribution of this phenomenon in nature suggests its functional importance. However, despite repeated attempts to understand the sense of the transformation of chromosomes into LBCs, many questions still remain open. The review critically examines all the main hypotheses explaining the functional importance of LBCs.