Patterns of polytene-chromosome replication in Simulium ornatipes (Diptera: Simuliidae)

Abstract

Double labelling of Simulium ornatipes polytene chromosomes with H3-and CiJ-thymidine shows that chromosome synthesis follows three distinct phases viz. a short phase of initiation in puffs and interbands spreading to more condensed regions; a long continuous labelling phase, then a discontinuously labelled end phase as bands complete their replication in temporal sequence. Analysis of H3 labelling patterns indicates that while heterochromatic bands replicate there is no clear correlation between heterochromatic or C-banding regions and band replication time. The major characteristic governing band replication time appears to be band size and density. However, in some bands this relationship is modified, perhaps it is suggested, by DNA organisation influencing the efficiency of replicons. The existence of great variability in homologous band replication times, even within a chromosome pair, indicates that the control of band replication is highly autonomous. It is suggested that polymorphisms at the molecular level determine this variation. Replication time of active nucleolar organisers is very long in contrast to the short replication of condensed inactive organisers. This may reflect differential polytenisation of ribosomal DNA as a result of a developmental polymorphism, or the amplification of ribosomal DNA by active nucleolar organisers.

Mitotic and salivary gland chromosome analyses in the Musca domestica L. (house fly) (Diptera: Muscidae)

“…In our studies, the size of the X chromosome in the diploid tissues was similar to that of the other autosomes, while it was much smaller in the salivary gland cells. These results suggest that, like Simulium ornatipes (Bedo, 1982b) and Chironomus melanotus (Steinemann, 1978), X liëtero-chromatin in the Musca domestica is underreplicated in a pronounced pattern. Similar results were obtained in Drosophila (Heitz, 1934;Gall, 1973), Sarcophaga bullata (Samols & Swift, 1979) and Lucilia cuprina (Bedo, 1982a).…”

Molecular phylogeny of black flies (Diptera: Simuliidae) from Thailand, using ITS2 rDNA

“…nuneztovari thousands of kilometers apart are small and are confined to only three regions of singlebase repeats and simple repeat motifs (Fritz et al, 1994). The possibility of there being more than one locus of the rDNA transcription unit in S. feuerborni, as found in Drosophila melanogaster (on the X and Y chromosomes) (Yagura, Yagura & Muramatsu, 1979) cannot be ruled out but is less likely because the rDNA transcription unit of Simulium species is located at the nucleolar organizing region on one chromosome arm, as found in chromosome arm IL of S. ornatipes (Bedo, 1982). Simulium feuerborni prefers to breed in small, shallow streams about 30 cm wide, with trailing grasses and fallen leaves at the Royal Project and Hui Sai Luaeng waterfall.…”

Replication timing in Drosophila and its peculiarities in polytene chromosomes

“…To determine the order of replication for different regions, various elegant methods were employed, such as double radioactive labeling, determination of the DNA amount in replicating bands, and analysis of patterns after natural or artificial synchronization of endocycles (Keyl, Pelling, 1963;Plaut et al, 1966;Danieli, Rodinò, 1967;Mulder et al, 1968;Amabis, 1974;Stocker, Pavan, 1974;Achary et al, 1981;Redfern, 1981). In different species, the replication time of a band correlates with the amount of DNA in it (Keyl, 1965;Mulder et al, 1968;Hägele, 1976;Bedo, 1982). Big bands replicate late and complete replication in a similar temporal order in different polytene tissues of Dro sophila (Sinha et al, 1987; and mosquito Anopheles stephensi (Redfern, 1981).…”