Review

The chromosomes of the Filariae

Rory Post^1,2

¹  Department of Entomology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK

²  Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK

Filaria Journal 2005, 4:10doi:10.1186/1475-2883-4-10

Published:	2 November 2005

Abstract

An understanding of the nature of the chromosomes of the filariae is expected to greatly assist the future interpretation of genome data. Filarial development is not eutelic, and there does not seem to be a fixed number of cell divisions in the way that there is in Caenorhabditis. It is not clear whether the chromosomes of the filariae have localized centromeres or whether they are holocentric. Sex determination is by a chromosomal "balance" X0 system in most filariae, but in some Onchocercidae there has been a chromosomal fusion to create a neo-XY system. It is presumed that the molecular basis of sex determination in filariae is similar to Caenorhabditis. The ancestral karyotype of the filariae is probably 5A+X0, but in some Onchocercidae this has been reduced to 4A+XY, and in O. volvulus and O. gibsoni it has been further reduced to 3A+XY. Onchocerca volvulus and O. gibsoni both have supernumary (B-) chromosomes and in O. volvulus there is a single active nucleolus organising region near the middle of the long autosome.