Rate of turnover of structural variants in the rDNA gene family of Drosophila melanogaster

Abstract

A high degree of polymorphism for the length and copy number of rDNA spacers, in both the X and Y chromosome clusters, has been found in a wild population of Drosophila melanogaster. The genetic behaviour of rDNA structural variants in separate and mixed populations derived from isofemale lines suggest that they are not subject to strong selection and are stable for over 1,000 generations. The high structural variability suggests an evolutionary rapid process of turnover in the family which could partly explain widespread sequence homogeneity (concerted evolution) of rDNA within a species.

Multiple Pol I initiation sequences in rDNA spacers ofDrosophila melanogaster

“…Fluctuations in the length of NTS's, both within and between Drosophila species, has been shown to be largely due to varying numbers of the 240 bp repeats (10,11,14). However, not all lengths can be accommodated in this manner and it is probable that both the 90 bp repeats and the 340 bp repeats also fluctuate in copy number.…”

“…It is clear from this and the above discussion that a critical feature of NTS function may be the maintenance of homologies between different regions of the ETS and NTS within the same species rather than conservation of a region between species. It is likely that the sequence homology between the initiation region and the putative initiation site sequences of the NTS is due both to the action of selection and to the action of molecular mechanisms of homogenisation which are acting on repeated families inDrosophila (10,11,27). Both these processes might ensure that sequence homogeneity between regions is maintained within a species at a time when sequence divergence accumulates between species (for full discussion see 28,29).…”

“…In this paper we present a detailed study of the sequence organisation of the NTS in Drosophila melanogaster. This is of particular interest since it is complemented by studies on the evolutionary dynamics of NTS sequence divergence and polymorphism in the sibling species of the melanogaster species subgroup of Drosophila (10,11).…”

The number of families of Triatoma dimidiata in a Guatemalan house

“…The house was inspected monthly for one man-hour (usually ½ hour by two people), revealing T. dimidiata with the age distribution shown in the Table. In addition, 40 T. dimidiata were collected from inside other houses in the village, and used as a background population for obtaining the population allele frequencies for all the loci. DNA was extracted from insect's legs according to the method described by Coen et al (1982) with modifications as described in Black and Munstermann (1996).…”

Polygene polymorphism affecting wing vein formation in a natural population of Drosophila melanogaster

“…Since gap frequencies were taken before the replicate cultures of lines I to 10 were separately labelled (la, ib, and so forth), we have estimated the correlation between gap frequencies and the average of the a and b culture chaeta numbers (r = -02, not significant). These lines also vary greatly in both the X and Y rDNA (Coen, Thoday, and Dover, 1982).…”