RESUMO
As a contribution towards detecting the genetic effects of low doses of genotoxic physical agents, this paper deals with the consequences of low-dose X-rays in the Aspergillus nidulans genome. The irradiation doses studied were those commonly used in dental clinics (1-5 cGy). Even very low doses promoted increased mitotic crossing-over frequencies in diploid strains heterozygous for several genetic markers including the ones involved in DNA repair and recombination mechanisms. Genetic markers of several heterozygous strains were individually analyzed disclosing that some markers were especially sensitive to the treatments. These markers should be chosen as bio-indicators in the homozygotization index assay to better detect the recombinogenic/carcinogenic genomic effects of low-dose X-rays.
Assuntos
Aspergillus nidulans/efeitos da radiação , Mitose/efeitos da radiação , Troca Genética/efeitos da radiação , Raios X , Aspergillus nidulans/genética , Diploide , Dano ao DNA , Homozigoto , Testes de Mutagenicidade , Mitose/genética , Relação Dose-Resposta à Radiação , Troca Genética/genéticaRESUMO
This paper presents a new method for detecting mitotic crossing-over in Aspergillus nidulans, based on the "homozygosity index" (HI) of recessive genes originally present in hetrozygosis in diploid strains, which occurs after mitotic crossing-over between the marker in question and the centromere. Since homozygous diploids (-/-) for auxotrophic markers can not grow in MM, homozygotization can be demonstrated by distorted mitotic segregation of the alleles involved. Two similar diploid strains (UT 448/UT 184 and Z1//UT 184), which differ by a chromosomic duplicate segment transposed from chromosome II to I in the Z1 haploid strain, were used. This excess of genetic material confers to the Z1 mutant the uvs character and makes Z1//UT 184 more unstable and sensitive to genotoxic agents, as evidenced by its high spontaneous recombinational index.