P. Michailova et al., CYTOGENETIC CHARACTERISTICS OF A POPULATION OF CHIRONOMUS-RIPARIUS MEIGEN 1804 (DIPTERA, CHIRONOMIDAE) FROM A POLLUTED PO RIVER STATION, Genetica, 98(2), 1996, pp. 161-178
A population of Chironomus riparius from a Po river station near Monca
lieri (a trace-metal polluted station) was studied. In this population
was established a great variability of band structure of polytene chr
omosomes as well as paracentric heterozygous inversions, deletions, de
ficiencies, partial breaks, diploid chromosome fragments, and changes
in functional activity and appearance of heterochromatin. In arms A th
rough F, some bands had an increased size compared to the standard chr
omosomic map. Some bands appeared in a heterozygous or normal homozygo
us state or were amplified. In all arms, many condensed stable bands a
ppeared in the decondensed state when compared to the standard map. As
ynaptic zones in arms E and G as well as heterozygous Balbiani rings a
nd NORs were established. Very often the 4th chromosome was almost com
pletely heteropycnotic and looked like a 'pompon' chromosome. For the
first time in this species, a high frequency of ectopic pairings of di
fferent arms was observed. Telomeric regions involved in ectopic pairi
ngs had a granular appearance, as did some centromeres. The hypothesis
is advanced that such a high frequency of structural rearrangements c
ould be correlated with genomic distribution of specific mobile elemen
ts.