In some eukaryotes, germline soma differentiation involves elimination of parts of the genome from somatic cells. The portions of the genome restricted to the germline often contain genes that play a role in development and function of the germline. Lineages with germline-restricted DNA are taxonomically diverse, and the size of the germline-restricted genome varies substantially. Unfortunately, few of these lineages have been studied in detail. As a result, we understand little about the general evolutionary forces that drive the origin and maintenance of germline-restricted DNA. One of the taxonomic groups where germline-restricted DNA has been poorly studied are the flies (Diptera). In three Dipteran families, Chironomidae, Cecidomyiidae, and Sciaridae, entire chromosomes are eliminated from somatic cells early in embryonic development. Germline-restricted chromosomes are thought to have evolved independently in the Dipteran families and their size, number, and transmission patterns vary between families. Although there is a wealth of cytological studies on these chromosomes in flies, almost no genomic studies have been undertaken. As a result, very little is known about how and why they evolved and what genes they encode. This review summarizes the literature on germline-restricted chromosomes in Diptera, discusses hypotheses for their origin and function, and compares germline-restricted DNA in Diptera to other eukaryotes. Finally, we discuss why Dipteran lineages represent a promising system for the study of germline-restricted chromosomes and propose future avenues of research on this topic.
Keywords: accessory chromosome; chromosome elimination; non-Mendelian inheritance; programmed DNA elimination; reproduction.
© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.