Gunnar Ising

A transposon as a cytogenetic marker in Drosophila melanogaster

SummaryWe have analyzed the behavior of a transposing element (TE) in Drosophila melanogaster. The TE carries the structural genes white (wa or waR=white apricot reversed) and roughest (rst+), which corresponds to the bands 3C2-6 and a genetic distance of approximately 0.7 map units. Due to the large size, TE can often be visualized in the polytene chromosomes as extra bands at the site of the transposon. We have identified over 100 different transpositions, most of which are situated in the large autosomes; genetic and cytological information is presented for 41 of these positions. Excision of TE may occur once in 1,000 chromosomes, while insertion in a new position is more rare, about once in 10,000 animals or less. The structure of TE itself is variable: regions within it may be lost, genes located adjacent to the site of insertion may transpose with the TE (“hitch-hiking” genes) or the TE may be duplicated.Possible mechanisms for transposition of the TE and its relation to “dispersed gene families” are discussed. Paro et al. (1983) have studied the end segments of the TE and isolated so-called FB elements (FB-NOF), which are responsible for its ability to transpose.A careful analysis of the many insertion points for TE will result in a more accurate correlation between the genetical and cytological maps for the two large autosomes of Drosophila melanogaster.

Minichromosomes in Drosophila melanogaster derived from the transposing element TE1

A minichromosome has originated from the transposing elementTE1. This autonomously replicating chromosome contains the structural genes white and roughest, from theDrosophila X chromosome. It arose within a stock carryingTE1 at 45F on chromosome2. In addition to thew andrst genes, the minichromosome may carry section 45C–45F from chromosome2. It is inherited by 33%–47% of the offspring. By this criterion it carries a centromere, although the origin of the centromere is unknown. From this minichromosome a still smaller one has originated, probably through the loss of all material from chromosome2 together with some heterochromatin. At the same time a duplication of white and roughest could have taken place. This chromosome has a strange morphology and is more frequently lost in meiosis than the larger one, but is still transmitted to about 29%–37% of the progeny of one parent heterozygous for the minichromosome. In both cases the flies have variegated eyes, probably as a result of position-effect variegation. The variegation pattern is influenced by factors in theX chromosome. The size of the smaller minichromosome is little more than 1 Mb as determined by pulsed field gel electrophoresis.

Characterization of a minichromosome derived from the transposing element TE1 in Drosophila melanogaster

The transposing element TEI contains the structural genes white and roughest from the Drosophilr X-chromosome. These genes are flanked by FB-elements, which are responsible for the mobility. At one ...