Difference In Mutation Frequency Research Articles

Phylogenetic and Evolutionary Implications of Interspecific Chloroplast DNA Variation in Krigia (Asteraceae-Lactuceae)

Chloroplast DNA restriction site and length variation was examined among 12 taxa of Krigia, using 34 restriction endonucleases, filter hybridization experiments, and comparative mapping procedures. A total of 252 restriction site mutations was detected, 159 of which were phylogenetically informative. The resulting phylogenetic trees correlated well with cytological and morphological data. The two sects. Krigia and Cymbia differed by at least 73 restriction site mutations. Most species within each section were characterized by many restriction site changes. Interspecific sequence divergence in Krigia was much higher than in any other previously studied genus of the Asteraceae and was comparable to the high levels of divergence found in genera of other angiosperm families. Relative rates of chloroplast DNA evolution in Krigia were significantly different among the various chromosome number groups, resulting in the rejection of a molecular clock. However, a molecular clock could not be rejected within each chromosome number group. Different regions of the chloroplast genome also showed extremely different frequencies of mutations and four hotspot areas were identified. The areas occurred in long spacer regions between gene coding sequences. Furthermore, most of the homoplasy and length variation also occurred within these hotspots. Chloroplast DNA trees were consistent with the hypothesis that an ancient allopolyploid event between species with low chromosome base numbers, followed by subsequent aneuploid reduction, resulted in K. wrightii with n = 9. The results also suggest that x = 5 is the probable ancestral base number for the genus and that aneuploid reduction is the major mode of chromosome number change in Krigia and related genera.

DNA repair and mutant frequency in schizophrenia

The in vivo frequency of mutants resulting from mutation at the hprt locus in human T-lymphocytes was determined with a cloning assay. T-lymphocytes were obtained from 14 individuals diagnosed with schizophrenia and 5 controls. No significant difference in mutant frequency was observed between the 2 groups. In addition, DNA-repair capacity was measured with the unscheduled DNA synthesis technique in lymphocytes from 7 individuals diagnosed with schizophrenia and 7 controls. Repair capacity was determined following treatment with MMS, MNNG, and 20 J/m2 ultraviolet light. No significant differences in DNA repair were observed between the patient and control groups in response to any of the 3 DNA-damaging agents. These results argue against differences between normal and schizophrenic individuals with respect to in vivo mutant frequency or their capacity to repair DNA lesions induced by MMS, MNNG, or ultraviolet radiation.

ENU mutagenesis in the mouse electrophoretic specific-locus test, 1. Dose-response relationship of electrophoretically-detected mutations arising from mouse spermatogonia treated with ethylnitrosourea

The mouse electrophoretic specific-locus test for induced germ-cell mutations, was used to determine the response of spermatogonial stem cells to a series of doses of the germ cell mutagen N-ethyl- N-nitrosourea (ENU). Male DBA/2J and C57B1/6J mice were treated with doses of 50, 100, 200 or 250 mg/kg ENU and their progeny screened for electrophoreticall--detectable mutations at 32 separate loci. As expected, increasing doses of ENU led to increasing mutant frequencies. The differences in mutant frequencies between treated DBA/2J and C57B1/6J males were not statistically significant.

Positive correlation between the occurrence of chromosome breakage and the induction of point mutations associated with male recombination 31.1 MRF system of hybrid dysgenesis in Drosophila melanogaster

One of the weak singed ( sn w) mutations, induced by the 31.1 MRF in the X-chromosome of a laboratory strain, is highly unstable, often changing to either a strong expression ( sn st) or reverting to wild type ( sn +). The present study shows that the X-chromosome carrying the ( sn w) mutation and the X-chromosome carrying one of the sn st alleles derived from the sn w mutation generate different frequencies of deletions associated with the w locus. Moreover, they produce different frequencies of mutations associated with the w locus in males after the reintroduction of the 31.1 MRF second chromosome. The occurrece of the deletions and the induction of the mutations are positively correlated and increase when flies are raised at a higher temperature. These data indicate that the induction of the w mutations follows the generation of chromosome breaks in the w locus. The break-points of the recovered deletions occurred in specific sites in the 3C subdivision. Furthermore both sn w and sn st X-chromosomes induce different frequencies of non-disjunction in females depending on the culture temperature and the genetic background. The present data also show that the 23.5 MRF second chromosome which exhibits specific differences in its activities from the 31.1 MRF is unable to induce w mutations. This fact supports our previous indications that the 31.1 MRF and the 23.5 MRF are not identical.

Hotspots for spontaneous and mutagen-induced lesions in regulatory subunit of cyclic AMP-dependent protein kinase in S49 mouse lymphoma cells.

From an S49 mouse lymphoma cell subline that carries an electrophoretic marker mutation in one allele for a regulatory (R) subunit of cyclic AMP-dependent protein kinase, 130 cyclic AMP-resistant mutants were isolated and characterized. Of the 77 independent spontaneous and mutagen-induced isolates identified, 74 had kinases with increased apparent activation constants (KaS) for cyclic AMP-dependent activation. The "Ka" phenotype was invariably correlated with an apparent structural lesion in one R subunit allele. "Charge-shift" lesions in 43 independent isolates were mapped to small regions within the R subunit by two-dimensional gel analysis of partial proteolysis peptides. Nine Ka mutations were distinguished by differences in charge or peptide maps of mutant R subunits, and the mutations were clustered in two regions associated with the cyclic AMP-binding sites of the R subunit. The relative frequencies of different mutations differed among spontaneous, ethyl methanesulfonate-induced, and N-methyl-N'-nitro-N-nitrosoguanidine-induced isolates. Mutation frequencies were also markedly different for the two R subunit alleles; this allele preference was strongest for mutagen-induced lesions in the more carboxy terminal cyclic AMP-binding site.

Dose response curves after irradiation of Arabidopsis seeds: a possible explanation for the “saturation” in mutant frequency at high radiation doses

Mutant frequency “saturation” in Arabidopsis' “main” inflorescence after fast neutron or X-ray treatment of seeds was observed using cell populations with heterogeneous radiation-sensitivities. Mutant frequencies were determined in (1) morphologically normal and conspicuous plants, (2) main and lateral inflorescences, and (3) different M 1-fertility classes. At moderate radiation doses (47 Gy fast neutrons and 233 Gy X-rays) significant differences in mutant frequencies between different M 1-fertility classes were observed. This suggests that cell populations with heterogeneous sensitivities were studied. No significant differences were observed either between the mutant frequencies in main and lateral inflorescences or between the ones in inflorescences of morphologically normal and conspicuous plants. This suggests that these inflorescences were formed by cell populations with similar but heterogeneous sensitivities.