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[en] Frequencies of induced recessive sex-linked lethal mutations (RSLLM) and dominant lethal mutations (DLM) were analyzed in genetically different Drosophila melanogaster strains w and MS after their exposure to radiation on radioactive soil in laboratory conditions. The RSLLM test applied to males after their 14-day radiation exposure yielded controversial results. An analysis of induced and spontaneous DLM demonstrated an increase in the frequency of early embryonic lethal mutations in the experiment (radiation exposure) in comparison with the control (spontaneous mutation rate) in both strains examined
[en] Highlights: • The mutation frequency is unnormalized. • While the mean mutation frequency is infamously erratic, the median mutation frequency is not an effective remedy. • Nonmutant cell death can inflate mutation frequencies. • The mutation rate should be the only yardstick of microbial mutability. - Abstract: The mutation frequency, also known as the mutant frequency, is an unnormalized quantity, and its normalized counterpart is the mutation rate. Due to historical reasons, the mutation frequency has been a predominant yardstick of microbial mutability in the field of mutator identification. While the mean mutation frequency is infamously erratic, replacing it with the median mutation frequency is not an effective remedy. By encouraging investigators to substitute mutation rates for mutation frequencies in microbial research, this paper directs attention to substantial open problems such as false positive control and massive nonmutant cell death.
[en] The stage at which homozygotes die was determined for 28 mutations (general symbol c*) at the albino (c) locus, of which 26 had earlier been found to be probably prenatally lethal. Within each of the mutant stocks, the uterine contents of c*/c/sup ch/ females, made pregnant either by c*//c/sup ch/ males (Ex series) or by c/sup ch//c/sup ch/ males (Co series), were examined between 13 and 17 days postconception. Altogether, 743 females were dissected and 7197 corpora lutea (representing ovulations) counted. In selected stocks, an additional 40 and 13 females were dissected on days seven or nine, respectively. In each of the 26 presumed prenatally lethal mutants, there was a deficiency of living fetuses in the Ex, as compared with the Co, group. Overall, this deficiency was 23.6% (expectation, 25% c*/c*). All meaningful excesses were in numbers eigher of moles (death shortly before, during, or just after implantation), or of early preimplantation losses. Homozygotes in none of the mutant stocks die between days nine and 19 postconception. Of 24 c-locus mutants known to be deficiencies since they lack the closely linked Mod-2, 13 clearly kill before implantation, ten around implantation, and one neonatally. The c and Mod-2 loci and the region between them are not needed for intrauterine survival. There are indications that the distinction between early-preimplantation death and implantation death may, in a general way, be related to length of the deficiency
[en] One of the fundamental aspects of genomes is the organization of the genes in packages known as chromosomes. All organisms from the simplest to the most complex possess chromosomes as part of their genome and they are characterized by a particular morphology and number characteristic of each species. Chromosome mutations induce changes that can originate in mitotic o meiotic errors in an individual, and these can become fixed in the population during evolution. This results either if the particular changes represent a selective advantage, or they may result in severe effects on the phenotype and fertility of its carriers that may be manifested as a genetic syndrome. In this essay I demonstrate how, using conventional and recent cytogenetic and molecular techniques we have begun understanding the function of chromosome arrangements in the differentiation of species and how particular defects or individual changes in the morphology or number of chromosomes can result in serious dysfunctions that are recognized as genetic syndromes.
[en] A recent paper by Mothersill and Seymour (1987), and its precursor by Seymour et al. (1986), prompt several comments. The points the letter makes are: (1) the dose-dependence of lethal mutations, or lethal sectoring, in a developing colony can depend upon the cells in question and/or the cell culture conditions which may apply; (2) lethal mutation probably depends upon radiation quality; (3) damage which may give rise to lethal mutations is very likely reparable; and (4) the dose-dependence of the frequency of induction of the neoplastic transformation of C3H 10T1/2 mouse cells, normalized to surviving cells, is probably not influenced by lethal mutations. The reply discusses the distinction between initiation and expression of transformation. (author)
[en] Pyruvate dehydrogenase (PDH) deficiency is one of the most common causes of congenital lactic acidosis. Correlations between the genetic defect and neuroimaging findings are lacking. We present conventional and diffusion-weighted MRI findings in a 7-day-old male neonate with PDH deficiency due to a mosaicism for the R302H mutation in the PDHA1 gene. Corpus callosum dysgenesis, widespread increased diffusion in the white matter, and bilateral subependymal cysts were the main features. Although confirmation of PDH deficiency depends on specialized biochemical analyses, neonatal MRI plays a role in evaluating the pattern and extent of brain damage, and potentially in early diagnosis and clinical decision making. (orig.)