Genome reorganization from polyteny to polyploidy in the nurse cells found in onion fly (Delia antiqua) and cabbage root fly (Delia radicum) ovaries (Diptera, Anthomyiidae).

The material required to ensure successful embryogenesis in the onion fly (Delia antiqua) and the cabbage root fly (Delia radicum) (Diptera, Anthomyiidae) is supplied by 15 nurse cells, while the oocyte chromosomes enter a quiescent stage during prophase I of meiosis. This level of transcription is achieved by the polyploidization of the nurse cell DNA. Elongate polytene chromosomes form in both species, but lack the banding and conspicuous puffing commonly seen in other dipteran tissues. The polytene chromosomes contract until they finally appear as small, densely staining spheres. These fragment into large numbers of endochromosomes that are much smaller than their mitotic counterparts, which then despiralize, resulting in the flocculate appearance of the nurse cell nucleus. Photodensitometry revealed a gradient of DNA values between nurse cells near the oocytes and those further away. Final DNA values 1000 times the haploid level were recorded in the nurse cell nearest to the oocyte compared with 336 times the C-value in the most distal cell. At lower temperatures (< 10 degrees C), the polytene chromosomes become banded and longer. None of the onion flies kept in these conditions produced viable eggs, though there was some reproductive success among the cabbage root flies.

Female meiosis in the onion fly and cabbage root fly (Diptera: Anthomyiidae).

The sequence of female meiosis was investigated in two populations of the cabbage root fly (Delia radicum) and three populations of the onion fly (D. antiqua). In contrast with the completely achiasmate males, both species showed high levels of recombination in females. However, significant differences in chiasma frequency occurred between individuals within populations and between the populations. It was not uncommon to find aneuploidy of the X chromosomes. The autosomes occasionally showed asynapsis or desynapsis, but normal disjunction of univalents was facilitated by distance pairing.

Cytogenetical aspects of morsitans tsetse flies with particular reference to Glossina pallidipes (Diptera, Glossinidae).

The basic diploid chromosome of Glossina pallidipes is 2n = 6 and includes a pair of large sub-metacentric autosomes (L1), a shorter pair of metacentric autosomes (L2), and an X and Y which constitute a heteromorphic pair. The male meiotic sequence, although similar to that of other tsetse species, is characterized by asynapsis between X and Y chromosomes, and only tenuous association between the autosomes. Giemsa C-banding characteristics are described for the chromosomes of five species/sub-species and by means of this technique a whole range of hitherto unsuspected polymorphisms have been discovered. Polytene chromosome maps of G. pallidipes have been prepared and a description of all principal cytological markers is provided. A detailed comparison between these chromosomes and those of G. austeni has been conducted, and the conclusion is that although they must share a common ancestor, extensive band differences and structural change have occurred during phylogeny.

Sumbionts in the female tsetse fly Glossina morsitans morsitans.

A rickettsia-like symbiont, located in the ovaries of G. m. morsitans is maternally transmitted to the offspring via the egg. It is suggested that they may be essential for normal ovarian development.