Chromosomal aberration assays are also used to detect chemicals that induce chromosome damage, including complex chromosome change such as rings, exchanges & dicentrics
and chromatid & chromosome breaks.
On exposure to bleomycin, there was a 7-fold increase in the frequency of cells with dicentrics
(0.27 per 100 cells) when compared to the index in negative control group (0.037 per 100 cells).
(a) Normal metaphase, (b) chromatid-type gap, (c) isochromatid gaps, (d) chromosome fragments, (e) chromosome with dicentrics
and the accompanying fragments, (f) Robertsonian translocation, (g) chromosome deletion, and (h) chromosomes with exchanged fragments.
Metaphase spreads obtained from treated cells showed an array of structural chromosomal aberrations in the form of chromatid fragmentation, p-p arm Robertsonian fusions, premature centromeric separation, dicentrics
, chromatid breaks, ring, end-to end fusion, endo-reduplication, markers, double minutes, tri- or quadric-radials.
The most common biological method is the cytogenetic technique based on the analysis of chromosome aberrations, especially dicentrics
(this method is more useful for whole-body exposures).
The following CSAs were observed: 45.1% acentric fragments, 18.3% dicentrics
, 2.1% chromosome-type breaks and 2.1% chromosome minute fragments.
Non-overlapping and well spread metaphase plates were selected for scoring chromosomal aberrations such as chromatid breaks, rings, chromatid exchanges, intrachromatid deletions, minutes, achromatic lesions, chromosome breaks, dicentrics
, triradials and RBI complexes.
The chromosomal aberrations (CAs) mainly observed were gaps, breakes, fragments and dicentrics
. Exchanges were rarely detected and less frequency of polyploids was also recorded in the exposed groups when compared to the respective control groups.
& Rings Deletions DONOR 400 cGy (5 + 400) cGy 400 cGy (5+400) cGy #1 136 92 52 51 #2 178 120 62 46 #3 79 50 39 15 #4 172 42 46 34 #5 134 106 58 41 Table 2.
Total CAs were subclassified as CSAs (including chromosome-type breaks, ring chromosomes, marker chromosomes, and dicentrics
) and chromatidtype aberrations (CTAs; including chromatidtype breaks and chromatid exchanges) (Hagmar et al.
The main advantages of scoring dicentrics
for biodosimetric evaluations are their high radiation specificity, low background in nonexposed individuals (0-1 dicentric
per 1000 cells), low intervariability, and low detection limits of 0.1 Gy for low linear energy transfer (LET) radiation (e.g., [gamma]- and X-rays) and 0.01 Gy for high LET radiations such as neutrons (3).
Chromatid-type aberrations such as breaks and exchanges and chromosome-type aberrations such as deletions and dicentrics