Acentric fragments

The test is used to detect DNA repair synthesis and for the detection of micronuclei in the cytoplasm of interphase cells. These micronuclei may originate from acentric fragments (chromosome fragments lacking a centromere) or whole chromosomes that are unable to migrate with the rest of the chromosomes during the... 

Occupational exposure of 20 workers to pentachlorophenol at concentrations that ranged from 1.2 to ISOpg /m for 3-34 years did not result in any increased incidence of sister chromatid exchanges or chromosomal aberrations. In another report, significant increases in the incidence of dicentric chromosomes and acentric fragments were detected in the peripheral lymphocytes of exposed workers the frequency of sister chromatid exchanges was not increased." ... 

Acentric fragments often are not incorporated into daughter nuclei at anaphase, but rather appear as micronuclei in the cytoplasm separate from the cell nucleus after cell division. The appearance of such micronuclei is a convenient manifestation of earlier chromosomal breakage, with loss of the distal fragment. Micronuclei can thus be used as an index of chromosomal breakage.392 Schmid394 has developed the bone marrow micronucleus test for use in experimental animals. 

There is inconclusive evidence that occupational exposure to metallic mercury and to organic and inorganic mercury compounds, primarily through inhalation, causes structural and numerical chromosome aberrations in human lymphocytes. In one study, significant increases in the frequency of acentric fragments (chromosome breaks) occurred in 4 workers exposed to high concentrations of metallic mercury and in 18 workers exposed to a mixture of mercuric chloride, methylmercuric chloride,... 

Figure 8.8 Human metaphase figure showing a dicentric chromosome (a) and an acentric fragment (b).

Ambon [Ref.] No. of persons examined Abbention x in acentric fragments cell dicentrics... 

When a single chromosomal break occurs in two different chromosomes (A and B), a new and important type of redistribution of genetic material—a translocation—takes place. In a translocation, a fragment of A may rejoin with a fragment of B. Thus, after breaking, each chromosome yields acentric fragments Aa and Ba and centric fragments A and B. Translocation may yield two types of combinations Aa and Be and A and Ba two monocentric chromosomes, or Aa and Ba and Ac and Be and an acentric and a dicentric chromosome. 

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