Origin, Composition, and Structure of the Supernumerary B Chromosome of Drosophila melanogaster
Year: 2018
Type: article
Abstract: ABSTRACT The number of chromosomes carried by an individual species is one of its defining characteristics. Some species, however, can also carry supernumerary chromosomes referred to as B chromosomes. B chromosomes were recently identified in a laboratory stock of Drosophila melanogaster —an established model organism with a wealth of genetic and genomic resources—enabling us to subject them to extensive molecular analysis. We isolated the B chromosomes by pulsed-field gel electrophoresis and determined their composition through next-generation sequencing. Although these B chromosomes carry no known euchromatic sequence, they are rich in transposable elements and long arrays of short nucleotide repeats, the most abundant being the uncharacterized AAGAT satellite repeat. Fluorescent in-situ hybridization on metaphase chromosome spreads revealed this repeat is located on Chromosome 4 , strongly suggesting the origin of the B chromosomes is Chromosome 4 . Cytological and quantitative comparisons of signal intensity between Chromosome 4 and the B chromosomes supports the hypothesis that the structure of the B chromosome is an isochromosome. We also report the identification of a new B chromosome variant in a related laboratory stock. This B chromosome has a similar repeat signature as the original but is smaller and much less prevalent. We examined additional stocks with similar genotypes and did not find B chromosomes, but did find these stocks lacked the AAGAT satellite repeat. Our molecular characterization of D. melanogaster B chromosomes is the first step towards understanding how supernumerary chromosomes arise from essential chromosomes and what may be necessary for their stable inheritance.
Source: Genetics
Language: English
Subfield: Plant Science
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W2901254230