| PubMed Abstract |
The segregation distorter (SD) complex is a naturally occurring meiotic drive system with the property that males heterozygous
for an SD-bearing chromosome 2 and an SD(+)-bearing homolog transmit the SD-bearing chromosome almost exclusively. This distorted
segregation is the consequence of an induced dysfunction of those sperm that receive the SD(+) homolog. From previous studies,
two loci have been implicated in this phenomenon: the Sd locus which is required to produce distortion, and the Responder
(Rsp) locus that is the site at which Sd acts. There are two allelic alternatives of Rsp-sensitive (Rsp(sens)) and insensitive
(Rsp(ins)); a chromosome carrying Rsp(ins) is not distorted by SD. In the present study, the function and location of each
of these elements was examined by a genetic and cytological characterization of X-ray-induced mutations at each locus. The
results indicate the following: (1) the Rsp locus is located in the proximal heterochromatin of 2R; (2) a deletion for the
Rsp locus renders a chromosome insensitive to distortion; (3) the Sd locus is located to the left of pr (2-54.5), in the region
from 37D2-D7 to 38A6-B2 of the salivary chromosome map; (4) an SD chromosome deleted for Sd loses its ability to distort;
(5) there is another important component of the SD system, E(SD), in or near the proximal heterochromatin of 2L, that behaves
as a strong enhancer of distortion. The results of these studies allow a reinterpretation of results from earlier analyses
of the SD system and serve to limit the possible mechanisms to account for segregation distortion.
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