Germline Hypermutability in Drosophila and Its Relation to Hybrid Dysgenesis and Cytotype
AUTOR(ES)
Engels, William R.
RESUMO
In its hypermutable state, an unstable singed allele, snw, mutates in the germline to two other alleleic forms at a total frequency usually between 40 and 60%. In its stable state, the mutation rate of snw is essentially zero. Its state depends on an extrachromosomal condition indistinguishable from a property called cytotype previously studied as a component of hybrid dysgenesis. Of the two known systems of hybrid dysgenesis, denoted P-M and I-R, snw hypermutability is determined by the P-M system and appears to be independent of the I-R system. Cytotype, as defined by the control of snw mutability, is self-reproducing in the cytoplasm or nucleoplasm of the germline through at least two generations. However, it is not entirely autonomous, being ultimately determined by the chromosomes after sufficiently many generations of backcrossing. This combination of chromosomal and extrachromosomal transmission agrees well with previous studies on cytotype. Temperature differences have little effect on the mean mutation rates, but they have a pronounced effect on the intrinsic variance among individuals. The latter effect suggests that high temperatures reduce germ-cell survival during the development of dysgenic flies. Chromosomal rearrangements produce no apparent effects on the behavior of snw. Hypermutability is thought to be caused by the excision or other alteration of an inserted genetic element in the snw gene. This element might be a copy of the "P factor," which is though to be a mobile sequence capable of causing female sterility and other dysgenic traits in the P-M system.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1214459Documentos Relacionados
- Sterility and Hypermutability in the P-M System of Hybrid Dysgenesis in DROSOPHILA MELANOGASTER
- Hybrid Dysgenesis in DROSOPHILA MELANOGASTER: The Genetics of Cytotype Determination in a Neutral Strain
- Transposase titration in Drosophila melanogaster: a model of cytotype in the P-M system of hybrid dysgenesis.
- Hybrid Dysgenesis in DROSOPHILA MELANOGASTER: Morphological and Cytological Studies of Ovarian Dysgenesis
- Hybrid Dysgenesis in Drosophila melanogaster: Evidence from Sterility and Southern Hybridization Tests That P Cytotype Is Not Maintained in the Absence of Chromosomal P Factors