Restriction map and α-amylase activity variation amongDrosophilamutation accumulation lines

Abstract

SummaryThe specific activities of α-amylase were measured for two sets of mutation accumulation lines, each set having originated from a different lethal-carrying second chromosome and SM1(Cy) chromosome and having been maintained by a balanced lethal system for about 300 generations. Significant variation was found to have accumulated among lines of both sets. Because of dysgenic crosses in the early generations of mutation accumulation, insertions or deletions of transposable elements in the Amy gene region were suspected of being the cause of this variation. In order to test this possibility, the structural changes in the 14 kb region of these chromosomes that includes the structural genes for α-amylase were investigated by restriction map analysis. We found that most part of the activity variation is due to replacements of a chromosomal region of SM1(Cy), including the structural genes for α-amylase, by the corresponding regions of the lethal chromosomes. One line also contained an insertion in this region but this line has an intermediate activity value. Thus, insertions of transposable elements into the Amy gene region were not found to be responsible for the new variation observed in α-amylase activity. If we remove those lines with structural changes from the analysis, the genetic variance of α-amylase specific activity among lines becomes non-significant in both sets of chromosomes.

Spontaneous mutations affecting glycerol-3-phosphate dehydrogenase enzyme activity in Drosophila melanogaster

“…Aquadro et al (1990) confirmed the increased ADH activity variation, and conducted a molecular analysis of a 13-kb Adh gene region. Unlike the results of Tachida et al (1989), no restriction map variation was found. Their restriction mapping analysis showed that the mobilization of transposable elements had not occurred in the Adh gene region in the chromosome lines used.…”

“…To understand the mechanisms by which variation is maintained, it is beneficial to study the composition of spontaneous mutations which affect enzyme activity. Tachida et al (1989) examined the restriction map variation in a 14-kb Amy gene region among chromosome lines that showed a significant variation in amylase enzyme activity. They found that the amylase activity variation was caused largely by a genetic change that had occurred in the region of the Amy structural gene.…”

Properties of spontaneous mutations affecting quantitative traits

“…Thus, a fraction of the viability decline observed during the early generations of Ohnishi's experiment could be non-mutational (Keightley, 1996 ;Garcı! a-Dorado, 1997), and could be attributed to an initial increase in the viability of the Cy reference chromosome through variation introduced by gene conversion or double crossingover (Tachida et al, 1989). This phenomenon may also apply to Mukai's experiments.…”