''Rhynchosciara americana'' is a species of fly. It has a life cycle of approximately 70 days, and the sibling larvae show a synchronized development. The larvae can reach one inch in length, and the adult fly is about 0.8 inch (20 mm). The larvae groups are usually originated from the same female posture and spin a communal cocoon where the metamorphosis will occur. The fly is scientifically notable for the physiology of its

polytene chromosome Polytene chromosomes are large chromosomes which have thousands of DNA strands. They provide a high level of function in certain tissues such as salivary glands of insects. Polytene chromosomes were first reported by E.G.Balbiani in 1881. Pol ...

s and developmentally regulated amplified puffs, first observed by

Crodowaldo Pavan Crodowaldo Pavan (; December 1, 1919 – April 3, 2009) was a Brazilian biologist and geneticist, and a scientific leader in Brazil. Early life Pavan was born to a family of second-generation immigrants from Italy in 1919, in the city of Campi ...

. Its ecology is poorly understood, but it is assumed to be a fungus gnat. Until recently, scientists had no success in the laboratory breeding of this fly. Entomologist

Christian Rudolph Wilhelm Wiedemann Christian Rudolph Wilhelm Wiedemann (7 December 1770 in Brunswick – 31 December 1840 in Kiel) was a German physician, historian, naturalist and entomologist. He is best known for his studies of world Diptera, but he also studied Hymenoptera a ...

first described and classified this species in his work ''Diptera Exotica'' (1821). He had analyzed Brazilian specimens probably sent to him by colleagues or enthusiasts. European entomologists had difficulty visiting Brazil to collect samples for political reasons at the time. In 1950, during an expedition to collect wild

Drosophilidae The Drosophilidae are a diverse, cosmopolitan family of flies, which includes species called fruit flies, although they are more accurately referred to as vinegar or pomace flies. Another distantly related family of flies, Tephritidae, are true f ...

in the shore, in

São Paulo state SAO or Sao may refer to: Places * Sao civilisation, in Middle Africa from 6th century BC to 16th century AD * Sao, a town in Boussé Department, Burkina Faso * Saco Transportation Center (station code SAO), a train station in Saco, Maine, U.S ...

on the southeast Brazilian coast

rediscovered the species and named it ''Rhynchosciara angelae''. In 1951 the first publication on this “new” dipteran describes its morphological aspects and some habits. The synonymy was demonstrated in 1969 by Martha Breuer, and ''R. angelae'' was corrected to ''R. americana''. Since the early observations the giant polytene chromosomes and its puffs were noticed in several larval tissues. Similar chromosomal structures were described in ''

Chironomus ''Chironomus'' is a genus of nonbiting midges in the subfamily Chironominae of the bloodworm family, Chironomidae, containing several cryptic species that can only be distinguished by experts based on the characteristics of their giant chromosome ...

'' by Balbiani, and became known as "Balbiani Rings", but the incorporation of radioactive

thymidine Thymidine (symbol dT or dThd), also known as deoxythymidine, deoxyribosylthymine, or thymine deoxyriboside, is a pyrimidine deoxynucleoside. Deoxythymidine is the DNA nucleoside T, which pairs with deoxyadenosine (A) in double-stranded DNA. I ...

experiments in the chromosomes of ''Rhynchosciara americana'' led to the discovery of two types of puff: a transcription-related puff, where the chromatin expands and the transcription events takes place; and an amplification-related one, where the chromatin expands and

RNA transcription Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode proteins are said to produce messenger RNA (mRNA). Other segments of DNA are copied into RNA molecules called ...

and

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...

occur. In fact it was the first biological model where disproportionate DNA replication was detected. Nowadays the amplification phenomena is well-documented in several organisms, as ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Ch ...

'', but is not totally understood. In ''Drosophila'' control elements as enhancers and replication origins were described and related to amplification phenomena, however in the Sciaridaes the puzzle is still far from solved.

References

* Pavan, C. and Breuer, M. E. 1952. Polytene chromosomes in different tissues of ''Rhynchosciara''. ''Journal of Heredity''. vol. 63, p. 151-157. * Pavan, C. 1967. Chromosomal changes induced by infective agents Triangle. ''Sandoz J. Med. Sci.'' vol. 8, p. 42-48. * Pavan, C., Biesele, J., Riess, R. W. and Wertz, A. V. 1971. XIII. Changes in the ultrastructure of ''Rhynchosciara'' cells infected by ''Microsporidia''. ''Studies in Genetics''. vol. VI, p. 7103. * Pavan, C., Da Cunha, A. B. and Morsoletto, C. 1971. Virus-chromosome relationships in cells of ''Rhynchosciara'' (''Diptera'', ''Sciaridae''). ''Caryologia''. vol. 24, p. 371-389. {{Taxonbar, from=Q7321720 Sciaridae Diptera of South America Insects described in 1821 Taxa named by Christian Rudolph Wilhelm Wiedemann