Discovery of supernumerary B chromosomes in Drosophila melanogaster.
B chromosomes are small, heterochromatic chromosomes that are transmitted in a non-Mendelian manner. We have identified a stock of Drosophila melanogaster that recently (within the last decade) acquired an average of 10 B chromosomes per fly. These B chromosomes are transmitted by both males and females and can be maintained for multiple generations in a wild-type genetic background despite the fact that they cause high levels of 4(th) chromosome meiotic nondisjunction in females. Most curiously, these B chromosomes are mitotically unstable, suggesting either the absence of critical chromosomal sites or the inability of the meiotic or mitotic systems to cope with many additional chromosomes. These B chromosomes also contain centromeres and are primarily composed of the heterochromatic AATAT satellite sequence. Although the AATAT sequence comprises the majority of the 4(th) chromosome heterochromatin, the B chromosomes lack most, if not all, 4(th) chromosome euchromatin. Presumably as a consequence of their heterochromatic content, these B chromosomes significantly modify position-effect variegation in two separate reporter systems, acting as enhancers of variegation in one case and suppressors in the other. The identification of B chromosomes in a genetically tractable organism like D. melanogaster will facilitate studies of chromosome evolution and the analysis of the mechanisms by which meiotic and mitotic processes cope with additional chromosomes.
Stowers Institute for Medical Research, Kansas City, Missouri 64110.
Elisabeth
E
Bauerly
Stacie E
SE
Hughes
Dana R
DR
Vietti
Danny E
DE
Miller
William
W
McDowell
R Scott
RS
Hawley
D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics; D002503:Centromere / Q000235:genetics; D059006:Chromosomes, Insect / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics; D004331:Drosophila melanogaster / Q000235:genetics*; D022041:Euchromatin / Q000235:genetics; D005260:Female; D014644:Genetic Variation; D006570:Heterochromatin / Q000235:genetics*; D008297:Male; D009630:Nondisjunction, Genetic; D032681:Spectral Karyotyping
D018797:Cell Cycle Proteins; D029721:Drosophila Proteins; D022041:Euchromatin; D006570:Heterochromatin; C531345:mtrm protein, Drosophila
meiosis; minichromosomes; mitotic instability; supernumerary chromosomes