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HYPOTHESIS: If trisected, then the head will regenerate first
The optimal use of biomarkers will most likely occur if environmental health research is linked not only to epidemiological studies but to studies of laboratory animals and cell lines and to the assessment of biomarkers in ecological studies of plants and animals in the wild (Shugart et al., 1992; Anderson et al., 1994). Biomarkers can serve as a common element in studies of these different groups or materials. Thus, a biomarker identified in an exposed laboratory animal or cell line might also be seen in wild or laboratory animals or humans with similar exposures. A parallelogram type approach (Sobels, 1993; Sutter, 1995) can be used to assess the relationship between markers and risks in those groups (Fig. 15). The parallelogram approach is derived from the 1970s work of Sobels (1993) to extrapolate damage from animals to humans. Genetic damage that cannot be measured directly, such as in human germ cells, can be estimated by measuring the same kind of damage in both germ cells and somatic cells of the mouse. With data on the induction of mutations or chromosome aberrations in both germ cells and somatic cells of the mouse, it is possible to estimate germ cell mutation frequencies in humans on the basis of what can be measured by monitoring genetic damage in human somatic cells (Sobels, 1993). Sutter (1995) has modified this approach to include to extrapolation. In the parallelogram experimental approach to knowledge of mechanism, data is used to test the hypothesis that a specific mechanism of action is conserved among rodent and human species (Sutter, 1995). Biomarkers can be used to reduce high to low dose and species extrapolation-related uncertainties by providing information on common mechanisms and the development of mechanistically based mathematical models (Sexton et al., 1995). The incorporation of biomarkers of exposure and susceptibility in physiologically based pharmacokinetic (PBPK) models has allowed for interspecies comparisons and enabled the simulation of different enzyme activities among individuals (Fennell et al., 1996). Biomarkers also may serve as an alternative to the use of PBPK models for determining dose (Rohmberg, 1995). They are particularly useful when they are more easily or accurately measured than the actual exposure. Since biomarkers have extraordinary sensitivity, they may significantly extend the range of empirical characterization of dose and response in cases where they may be detected and measured at dose levels below those at which other effects are directly observable (Rohmberg, 1995; Ehrenberg et al., 1996). For example, adduct measurements of some alkylating agents may be used to indicate disease risks at levels too low to be detected by epidemiological means (Ehrenberg et al., 1996).
The classic Ames test was further extended to include a molecular genetic investigation, allowing students to see firsthand the direct connection between a phenotype (His− and His+) and DNA sequences. Students choose a revertant colony for study, extract genomic DNA, use PCR to amplify large regions of the affected genes, use a core facility to produce DNA sequence, align and analyze the resulting sequences, and correlate to phenotype. The procedures that we designed have been 97% effective in producing usable molecular data (base sequences). DNA preps using Qiagen's DNAeasy kit, PCR done with Promega's clear master mix, and the indicated thermocycling have never failed with our protocols, obviating the need for an intermediate step of gel electrophoresis. DNA sequences and chromatograms arrive from core facilities as electronic files, and freely available software is used to align and compare sequences. Students will still need to use their own common sense, however, when comparing frameshift alleles, as the simple alignment tool does not always “see” insertions or deletions as well as the human eye.
Cancer Genetics Risk Assessment and ..
The application of urine as a source of adducts for biomonitoring has been reviewed (Shuker & Farmer, 1992). The advantages of using urinary adducts as the measure of exposure to genotoxic compounds include non-invasiveness, large amounts of adducts available and at least in some cases relatively simple purification of adducts. The main disadvantage is that the molecular origin of the adducts is unknown, whether it is DNA, RNA or free nucleosides. Owing to abundance, cytoplasmic location and fast turn-over, RNA adducts are likely to overwhelm DNA adducts unless thymine adducts are investigated. The tissue source is also unknown and dietary sources may confound the results. If dietary sources can be excluded, urinary adducts represent an integrated measure of whole body dose for carcinogens. However, kinetic parameters of DNA adduct formation and repair in human tissues are almost completely unknown and any quantitative assessment of data will be arbitrary.
This overview reviews key concepts and learning activities to help students understand how genes influence our traits by molecular processes. Topics covered include basic understanding of the important roles of proteins and DNA; DNA structure, function and replication; the molecular biology of how genes influence traits, including transcription and translation; the molecular biology of mutations; and genetic engineering. To help students understand the relevance of these molecular processes, the suggested learning activities link alleles of specific genes to human characteristics such as albinism, sickle cell anemia and muscular dystrophy. Suggested activities include hands-on laboratory and simulation activities, web-based simulations, discussion activities and a vocabulary review game. (NGSS)
Why regulators conclude glyphosate safe while IARC, …
In addition to being indicators for exposure, DNA adducts would appear excellent tools in carcinogen metabolism and DNA repair work. However, this area has been underdeveloped because the methods for adduct determination have not been available for specific adducts in humans. Large amounts of work have been devoted to study relationships between metabolic phenotypes/genotypes and cancer, with an implied assumption that DNA-damaging metabolites are involved. The results have been a bewildering collection of contradictory data. However, recently, when specific DNA methods have been applied, coherent results on the effects of certain metabolic genotypes have begun to emerge (Bartsch et al., 1998; Hou et al., 1999; Thompson et al., 1999; Lunn et al., 1999). More details are presented in Appendix 3.
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