Dose Of Mutagen Research Articles

Induction of chlorophyll mutants in Zingiber officinale Roscoe by Gamma Rays and EMS

The present investigation comprises the data on frequency percentage of chlorophyllmutations in the different doses of gamma rays coupled with EMS in ginger. Different mutationfrequencies and width of mutation spectra were induced under the action of differentconcentrations of the two applied mutagens. The spectrums of chlorophyll mutations (albino,xantha, and chlorina) were observed and grouped. The overall mutation spectrum for gingershowed that xantha occurred with the highest frequency, followed by chlorina and albino. Themutagenic effectiveness decreased with the increase in dose of mutagen for both the mutagenindicating that negative relationship between effectiveness and dose of mutagen. EMS providedmore number of chlorophyll mutants than gamma rays in this investigation.

EFFECT OF RADIATION AND CHEMICAL MUTAGEN ON VARIABILITY IN SAFFRON (CROCUS SATIVUS L.)

Corms at different stages of growth rate were subjected to different doses of physical and chemical mutagens. The study revealed that Colchicine (0.05%) was found beneficial for enhancing pistil length, leaf number and leaf length with a negative effect on survival corm treatment with radiation dose of 0.2 kr, EMS (0.1%) and Ethidium Bromide (0.2%) showed significant positive effect on survival, increased number of heavier flowers and pistil weight. Mutagens induced morphological and anatomical variants showing increased number of stomata, thicker and broader leaves. Floral variant induced in M1 through 0.2 kr radiation had no genetic base and was purely environmental. Resting bud stage (1 st -15 th June) has been identified as appropriate stage for inducing variation through physical and chemical mutagens. Plants showing variability have been tagged and will be studied during ensuring season.

Induced Mutagenesis for Improvement of Garden Pea

Induced mutation has become an effective tool to improve a crop through creation of variability. Seeds of Garden pea (Pisum sativum L.), cvs. Arkel and Azad P-1, were exposed to mutagens in 2004 to 2006. The M1 generation was produced from these mutagen-treated seeds. A wide range of chlorophyll and viable morphological mutations were obtained in the M2 generations (subsequent generation derived from seed harvested in M1). Additional seeds of the cultivars were treated with doses of 60Co gamma rays and ethyl methane sulphonate (EMS) from 2004 to 2006 to isolate more desirable mutants. Chlorophyll mutation rate in the M2 generations increased as gamma irradiation dose and concentration of EMS increased. Frequency of viable mutants was, in general, higher in treatments with EMS than with gamma rays, with the exception of gamma irradiated ‘Azad P-1’ in 2006. The frequency of total mutants increased with increasing dose of mutagens at similar rates in cultivars over years. Among chlorophyll mutants, frequency of the xantha type (pale yellow colored seedlings) was higher followed by chlorina (yellowing of leaf) and albina type (completely devoid of chlorophyll) mutants. Treatment with 0.3% EMS was, in general, more effective in inducing desirable mutations at the highest frequency, and ‘Arkel’ had more positive mutations than ‘Azad P-1’. The desirable mutants of long and dark green pods, three or more flowers or pods on a peduncle, profuse branching and pod bearing, short internodes, dark green pods, and male sterility were isolated from different treatments over years. Lethality or biological injury, manifested as reduced germination, increased with increasing dose of gamma rays and EMS. Mutagenic effectiveness and efficiency generally increased with increasing EMS dose. Mutation breeding can play a role in pea improvement to induce useful variability of desirable traits to develop improved genotypes.

Lethal mutagenesis in a structured environment

We analyze how lethal mutagenesis operates in a compartmentalized host. We assume that different compartments receive different amounts of mutagen and that virions can migrate among compartments. We address two main questions: (1) To what extent can refugia, i.e., compartments that receive little mutagen, prevent extinction? (2) Does migration among compartments limit the effectiveness of refugia? We find that if there is little migration, extinction has to be achieved separately in all compartments. In this case, the total dose of mutagen administered to the host needs to be so high that the mutagen is effective even in the refugia. By contrast, if migration is extensive, then lethal mutagenesis is effective as long as the average growth in all compartments is reduced to below replacement levels. The effectiveness of migration is governed by the ratio of virion replication and death rates, R 0 . The smaller R 0 , the less migration is necessary to neutralize refugia and the less mutagen is necessary to achieve extinction at high migration rates.

Counteracting Quasispecies Adaptability: Extinction of a Ribavirin-Resistant Virus Mutant by an Alternative Mutagenic Treatment

BackgroundLethal mutagenesis, or virus extinction promoted by mutagen-induced elevation of mutation rates of viruses, may meet with the problem of selection of mutagen-resistant variants, as extensively documented for standard, non-mutagenic antiviral inhibitors. Previously, we characterized a mutant of foot-and-mouth disease virus that included in its RNA-dependent RNA polymerase replacement M296I that decreased the sensitivity of the virus to the mutagenic nucleoside analogue ribavirin.Methodology and Principal FindingsReplacement M296I in the viral polymerase impedes the extinction of the mutant foot-and-mouth disease virus by elevated concentrations of ribavirin. In contrast, wild type virus was extinguished by the same ribavirin treatment and, interestingly, no mutants resistant to ribavirin were selected from the wild type populations. Decreases of infectivity and viral load of the ribavirin-resistant M296I mutant were attained with a combination of the mutagen 5-fluorouracil and the non-mutagenic inhibitor guanidine hydrocloride. However, extinction was achieved with a sequential treatment, first with ribavirin, and then with a minimal dose of 5-fluorouracil in combination with guanidine hydrochloride. Both, wild type and ribavirin-resistant mutant M296I exhibited equal sensitivity to this combination, indicating that replacement M296I in the polymerase did not confer a significant cross-resistance to 5-fluorouracil. We discuss these results in relation to antiviral designs based on lethal mutagenesis.Conclusions(i) When dominant in the population, a mutation that confers partial resistance to a mutagenic agent can jeopardize virus extinction by elevated doses of the same mutagen. (ii) A wild type virus, subjected to identical high mutagenic treatment, need not select a mutagen-resistant variant, and the population can be extinguished. (iii) Extinction of the mutagen-resistant variant can be achieved by a sequential treatment of a high dose of the same mutagen, followed by a combination of another mutagen with an antiviral inhibitor.

The effect of natural fermented milk in the protection of liver from cancer

PurposeThe purpose of this paper is to evaluate the protective effect of natural fermented milk (NFM) against liver cancer.Design/methodology/approachFive types of NFM were collected from different places around Makka. The natural flora which present in them were studied and certain types which contain Lactobacillus spp. and Bifidobacterium spp. strains were selected to be used in the research. The nutritional experiment was carried out on 20 Albino mice divided into four groups. The first group (A) was control (not fed on NFM). The second (B) and third (C) groups were fed daily on (NFM) for two weeks. The final group (D) received basal diet only for four weeks, but after two weeks the third and fourth groups were treated orally by one dose of toxic mutagen (0.25 mg/mouse). The quality of life was measured by: specific strain count in stool; histopathological and histochemical studies on liver; and lymphocytic count.FindingsCow's milk which contains Lactobacillus spp. and Bifidobacterium spp. has a protective effect depending on its anti‐microbial properties. Also it enhances the endogenous intestinal probiotic bacteria that have several beneficial effects (i.e. detoxification and antigen toxicity) and stimulation of immune modulator cells.Originality/valueThe paper evaluates the protective effect of natural fermented milk (NFM) against cancer of the liver.

Spectrum of mutational events in the absence of DOG-1/FANCJ in Caenorhabditis elegans

The Caenorhabditis elegans ortholog of the Fanconi anemia pathway component J (FANCJ) is DOG-1, which is essential for genome stability. Previous studies have shown that disruption of the dog-1 gene generates small deletions of poly-C/poly-G tracts detectable by PCR and results in a mutator phenotype. In this paper, we describe the isolation and characterization of lethal mutations resulting from the loss of dog-1 function. The mutant strains were analyzed using a combination of techniques including genetic mapping, SNP mapping, and oaCGH (oligo array Comparative Genome Hybridization). Using the eT1 balancer system to recover lethal mutants, we isolated, in addition to small deletions, large chromosomal rearrangements, including duplications, translocations and deficiencies. The forward mutation frequency was 10-fold higher than the spontaneous frequency for eT1, and equivalent to that observed for low doses of standard mutagens. From a screen for suppressors of mdf-1/MAD1 lethality, we previously had isolated such-4(h2168), shown here to be a large tandem duplication. Thus, the range of mutational events caused by lack of DOG-1/FANCJ is much broader than previously described.

Mutagenesis in Petunia x hybrida Vilm. and isolation of a novel morphological mutant

Traditionally, mutagenesis has been used to introduce novel genetic variability in ornamental crops. More recently, it has become a powerful tool in gene discovery and functional analyses in reverse genetics approaches. The present work aimed to compare the efficiency of physical and chemical agents in generating mutant populations of petunia. We have indirectly evaluated the genomic damage by analyzing developmental characteristics of the plantlets derived from treated seeds employing gamma radiation at 0, 20, 40, 60, 80 and 100 Gy and the alkylating agent ethyl-methanesulfonate (EMS) at 0, 0.05, 0.1, 0.15, 0.2 and 0.25% (v/v). Gamma rays and EMS caused developmental defects and decreased seedling viability in plants obtained from the mutagenized seeds. High mutagen doses reduced in approximately 44% the number of plants with primary leaves at 15 days after sowing (DAS) and decreased seedling survival rates to 55% (gamma) and 28% (EMS), in comparison to untreated controls. Seedling height decrease was proportional to increasing EMS dosage, whereas 40 and 60 Gy of gamma irradiation caused the most significant reduction in height. Moderate DNA damage allowing a high saturation of mutant alleles in the genome and the generation of viable plants for reverse genetics studies was correlated to the biological parameter LD50, the dose required to kill half of the tested population. It corresponded to 100 Gy for gamma radiation and 0.1% for EMS treatment. The optimized mutagen treatments were used to develop petunia mutant populations (M1 and M2) and novel morphological mutants were identified.

The effects of sodium azide and colchicine treatments on morphological and yield traits of sesame seed (Sesame indicum L.)

Seeds of Sesame (Sesame indicum L.) were exposed to varying concentrations of sodium azide and colchicine solutions ranging from 0 - 0.250% (w/v). Variations in the percentage germination and survival, number of days to maturity, plant heights, total leaf area/plant, chlorophyll content, pollen sterility, dry matter and fruit size were recorded in the C1 and C2 generations. The frequency of mutation/injury increased with increasing concentrations of the mutagens. The LC50 values based on survival percentages in the M1 generation were fixed at 0.0776 and 0.0473% for sodium azide and colchicine respectively. There were dose related effects of the mutagenic treatments on quantitative traits resulting in reductions in traits such as germination and survival percentages, plant height, number of fruit/plant, but increases in leaf area, maturity time and fruit size. Colchicine treatment produced shortened internodes, deformed leaves, and chlorophyll mutants. Low doses of both mutagens (<0.125%) produced early maturing variants and robust/high yields and can be imposed to obtain beneficial mutants in sesame. Key words: Sodium azide, Colchicine, Sesame, Seeds, Mutagenic effects

Nonstochastic heritable cell lethality in the practice of biotesting of man-made pollutants as inducers of aftereffects

A nonstochastic heritable cell lethality effect was for the first time used in the practice of biotesting in a model of Saccharomyces yeasts for predicting the hazard of low mutagen doses. It was demonstrated that the heritable cell lethality might be induced by multicomponent mutagens of a technogenic nature, for example, sewage waters of gas-transferring plants. The possibility of extrapolation of the results to multicellular organisms is discussed.

The effects of sodium azide and colchicine treatments on morphological and yield traits of sesame seed (Sesame indicum L.)

Seeds of Sesame (Sesame indicum L.) were exposed to varying concentrations of sodium azide and colchicine solutions ranging from 0 - 0.250% (w/v). Variations in the percentage germination and survival, number of days to maturity, plant heights, total leaf area/plant, chlorophyll content, pollen sterility, dry matter and fruit size were recorded in the C1 and C2 generations. The frequency of mutation/injury increased with increasing concentrations of the mutagens. The LC50 values based on survival percentages in the M1 generation were fixed at 0.0776 and 0.0473% for sodium azide and colchicine respectively. There were dose related effects of the mutagenic treatments on quantitative traits resulting in reductions in traits such as germination and survival percentages, plant height, number of fruit/plant, but increases in leaf area, maturity time and fruit size. Colchicine treatment produced shortened internodes, deformed leaves, and chlorophyll mutants. Low doses of both mutagens (<0.125%) produced early maturing variants and robust/high yields and can be imposed to obtain beneficial mutants in sesame.

Mutagenic Activity of a Mixture of Heterocyclic Amines at Doses below the Biological Threshold Level of Each

The combined mutagenic effects of six heterocyclic amines (Trp-P-1, Trp-P-2, Glu-P-1, Glu-P-2, MeIQ, and IQ) at doses below the biological threshold level of each were investigated in the reverse mutation assay with Salmonella typhimurium. The lowest mutagenic doses of heterocyclic amines in TA1978P (hisD3052, rfa/pKM101) were 40 to 200 times the lowest mutagenic doses in TA98 (hisD3052, rfa, uvrB/pKM101), a strain deficient in nucleotide excision repair. The six heterocyclic amines were mixed at doses below the biological threshold that were mutagenic to TA98 but not to TA1978P. A significant increase in the number of revertants in TA1978P was observed with combined heterocyclic amines. The results suggest that DNA adduct formation at doses below the biological threshold level was additive, with the total amount reflecting the mutagenicity. We should consider the potential for additive effects of mutagens when we consider biological thresholds, because most of environmental mutagens exist in complex mixtures of chemicals.

Effects of ion beam irradiation on adventitious shoot regeneration from in vitro leaf explants of Saintpaulia ionahta

The effects of 960 MeV carbon ion beam and 8 MeV X-ray irradiation on adventitious shoots from in vitro leaf explants of two different Saintpaulia ionahta (Mauve and Indikon) cultivars were studied with regard to tissue increase, shoots differentiation and morphology changes in the shoots. The experimental results showed that the survival fraction of shoot formation for the Mauve and Indikon irradiated with the carbon ion beam at 20 Gy were 0.715 and 0.600, respectively, while those for both the cultivars exposed to the X-ray irradiation at the same dose were 1.000. Relative biological effectiveness (RBE) of Mauve with respect to X-ray was about two. Secondly, the percentage of regenerating explants with malformed shoots in all Mauve regenerating explants irradiated with carbon ion beam at 20 Gy accounted for 49.6%, while that irradiated with the same dose of X-ray irradiation was only 4.7%; as for Saintpaulia ionahta Indikon irradiated with 20 Gy carbon ion beam, the percentage was 43.3%, which was higher than that of X-ray irradiation. Last, many chlorophyll deficient and other varieties of mutants were obtained in this study. Based on the results above, it can be concluded that the effect of mutation induction by carbon ion beam irradiation on the leaf explants of Saintpaulia ionahta is better than that by X-ray irradiation; and the optimal mutagenic dose varies from 20 Gy to 25 Gy for carbon ion beam irradiation.

A single-molecule PCR approach to the measurement of induced expanded simple tandem repeat instability in vitro

Sensitive and precise models are needed to identify potential genotoxicity at environmentally relevant doses of mutagens. The size length alterations in expanded simple tandem repeat (ESTR) loci have been used as a biomarker of genetic instability caused by a variety of agents in the mouse germline. The mechanisms operating in both spontaneous and induced instability are poorly understood. We have developed a single-molecule polymerase chain reaction (SM-PCR) method to investigate mutation at the mouse ESTR locus Ms6-hm in the murine C3H/10T1/2 embryonic cell line. Growth of cells to levels of high cell density induced increased ESTR instability, with mutation frequencies 5.1-fold (±2.8) over sub-confluent cultures. Accordingly, cell cultures were maintained at sub-confluent levels for further investigations of the induction of ESTR mutation by genotoxic agents. Treatment with the DNA alkylating agent N-nitroso- N-ethylurea (ENU) resulted in a 1.94-fold (±1.1) increase in mutation frequency, similar to responses measured previously in the germline in vivo. Therefore, mutagen exposure can also affect somatic (non-meiotic) rapidly dividing mouse cells. This SM-PCR approach eliminates the requirement of sub-cloning individual treated cells, thereby, reducing the time needed to screen for ESTR mutation, and will be a very useful tool for future investigations into the mechanisms involved in ESTR mutation.

3,4‐Epoxy‐1‐butene, a reactive metabolite of 1,3‐butadiene, induces somatic mutations in Xpc‐null mice

Xpc-null (Xpc-/-) mice, deficient in the global genome repair subpathway of nucleotide excision repair (NER-GGR), were exposed by intraperitoneal (i.p.) injection to a 300 mg/kg mutagenic dose of 3,4-epoxy-1-butene (EB), to investigate NER's potential role in repairing butadiene (BD) epoxide DNA lesions. Mutagenic sensitivity was assessed using the Hprt assay. Xpc-/- mice were significantly more sensitive to EB exposure, exhibiting an average 2.8-fold increase in Hprt mutant frequency (MF) relative to those of exposed Xpc+/+ (wild-type) mice. As a positive control for NER-GGR, additional mice were exposed by i.p. injection to a 150 mg/kg mutagenic dose of benzo[a]pyrene (B[a]P). The Xpc-/- mice had MFs 2.9-fold higher than those of exposed Xpc+/+ mice. These results suggest that NER-GGR plays a role in recognizing and repairing some of the DNA adducts formed following in vivo exposure to EB. Additional research is needed to examine the response of Xpc-/- mice, as well as other NER-deficient strains, to inhaled BD. Furthermore, it is likely that alternative DNA repair pathways also are involved in restoring genomic integrity compromised by BD-epoxide DNA damage. Collaborative studies are currently underway to address these critical issues.

On Antimutagenesis Mechanism in Plants

The effect of nitrosylmethylurea (NMU) on the mitotic index and the frequency of cells with aberrations, as well as the effects of pre- and posttreatment with antioxidant ambiol on the NMU effects were studied on seedlings of common winter wheat Triticum aestivum, cultivar Moskovskaya 39. Both pre- and posttreatment with ambiol resulted in antimutagenic effect but after posttreatment, the effect was lower. Irrespective of type of seedling treatment with ambiol and the time of their fixation (45, 48, and 51 h), when mitotic index is plotted versus frequency of cells with aberrations, all experimental points fall on the same regression line with coefficient of correlation of -0.82 (P < 0.001). This implies that the same mechanism underlies antimutagenic effect irrespective of when the antimutagen was applied, before or after the knockout mutagen dose. This also suggests that the antimutagenic effect is independent of the degree of the mutagen-induced damage, because by the time of posttreatment, the volume of genome damage is already determined and the antimutagen fails to change it. Finally, this suggests that irrespective of time of antimutagen treatment, the mutation frequency is reduced by the mechanism of stimulated repopulation.

Comparação entre mutagênicos químico e físico em populações de aveia

Comparou-se a campo a variabilidade genética em populações de aveia hexaplóide tratadas com agentes mutagênicos físico e químico, através do caráter ciclo vegetativo de plantas. Foram realizados experimentos em duas safras agrícolas em Pelotas, RS, em 1997/98 e 1998/99. As sementes foram irradiadas no Centro Regional de Oncologia da Faculdade de Medicina da UFPel, com uma taxa de dose de 0,25Gy min-1. As doses totais absorvidas para o mutagênico físico foram 100, 200 e 400Gy e, para o mutagênico químico 0,5, 1,5 e 3,0% por tratamento de 1200 sementes aproximadamente, em cada genótipo fixo de aveia avaliado. Foi obtida diferença na eficiência entre os agentes mutagênicos testados. O agente mutagênico físico foi sempre superior em relação ao agente mutagênico químico, independente da geração segregante avaliada, proporcionando assim um incremento maior no número de classes fenotípicas, tanto para redução quanto para o aumento do número de dias entre a emergência e o florescimento. Os genótipos mostraram sensibilidade diferenciada em relação à dose dos agentes mutagênicos avaliados, indicando que a eficiência dos tratamentos em alterar a variabilidade genética para precocidade e aumento do ciclo vegetativo foi variável. De modo geral, os dados indicaram decréscimo do caráter ciclo vegetativo com o acréscimo da dose dos agentes mutagênicos testados. O estudo das populações UPF-16 nas doses 100 e 200 gray submetidas ao tratamento com o agente mutagênico físico apontaram o maior grau de divergência genética e de dominância para o caráter ciclo vegetativo de plantas.

Similar Mutagenicity of Photoactivated Porphyrins and Ultraviolet A Radiation in Mouse Embryonic Fibroblasts: Involvement of Oxidative DNA Lesions in Mutagenesis

Ultraviolet A (UVA) radiation is implicated in the etiology of human skin cancer. However, the underlying mechanism of carcinogenicity for UVA is not fully delineated. A mutagenic role for UVA has been suggested, which involves activation of endogenous photosensitizers generating oxidative DNA damage. We investigated the mutagenicity of UVA alone and in combination with delta-aminolevulinic acid (delta-ALA), a precursor of the intracellular photosensitizers porphyrins, in transgenic Big Blue mouse embryonic fibroblasts. A significant generation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), a typical promutagenic oxidative DNA lesion, was observed in cells treated with a combination of delta-ALA (1 mM) and UVA (0.06 J/cm(2)) as quantified by high-pressure liquid chromatography-tandem mass spectrometry (p < 0.001; relative to the control). The steady-state level of 8-oxo-dG, however, remained unchanged in cells irradiated with UVA or treated with delta-ALA alone. Other photolesions including cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone photoproducts were not detectable in cells treated with delta-ALA and/or irradiated with UVA as determined by terminal transferase-dependent polymerase chain reaction assay. Mutation analyses of the cII transgene in cells treated with a combination of delta-ALA and UVA showed an approximately 3-fold increase in mutant frequency relative to the control (p < 0.008), as well as a unique induced mutation spectrum as established by DNA sequence analysis (p < 0.005; 95% CI, 0.002-0.009). No mutagenic effects were observed in cells irradiated with UVA or treated with delta-ALA alone. The spectrum of mutations produced by delta-ALA plus UVA was characterized by a significantly increased frequency of G --> T transversions (p < 0.0003; relative to the control), which are the hallmark mutations induced by 8-oxo-dG. Notably, the 8-oxo-dG-mediated mutagenicity of UVA plus delta-ALA is similar to that established previously for UVA alone at a mutagenic dose of 18 J/cm(2). We conclude that, in the presence of exogenous photosensitizers, UVA at a nonmutagenic dose induces mutations through the same mechanism as does a mutagenic dose of UVA per se.

Intensity-modulated radiation therapy: The inverse, the converse, and the perverse

Intensity-modulated radiation therapy (IMRT) is a refinement of current radiotherapy techniques rather than a major breakthrough. The term IMRT includes several different techniques that all share with classical arc therapy the principle of using multiple fields to reduce the dose to normal tissues, but integrating to a higher dose throughout the tumor volume itself. This paper reviews not only the putative upside but also the downside of the development of IMRT. Theoretical, practical, and cost considerations, both positive and negative, are discussed. There are several issues to be considered, but the most important perversely predict a significant increase in radiation-induced neoplasms, resulting not only from larger volumes of tissue exposed to more modest but still mutagenic doses, but also from a significant increase in total body dose from leakage, because the beam is typically on for a considerably longer period of time than is conventional. A plea is made for radiation oncologists to maintain a strong biologic and cellular orientation as oncology rapidly becomes more molecular in its orientation.

The effect of dietary restriction during development in utero on the frequency of spontaneous somatic mutations.

Caloric or dietary restriction is known to be protective against cancer in humans and in mice but the mechanism is uncertain. Given that somatic mutations are important in carcinogenesis, dietary restriction may act by changing mutation rates. Indeed, previous studies have shown that reductions in caloric intake during development or in adult life make mice less susceptible to high doses of mutagens. In these studies there have been hints that the spontaneous mutant frequency may also be reduced, but no significant decrease has been observed save in one study of very old mice. Since the spontaneous mutant frequency is already low, reductions from this level require the use of much larger sample sizes than usual and larger than those used in the previous studies. As pre-existing mutations cannot be eliminated, it is necessary to reduce the dietary intake over a period of time when a substantial proportion of spontaneous mutations arise in order to see an effect. To overcome such problems, the dietary restriction in this study was applied during the time of the highest mutation rate, early development, and many more than the usual number of animals were studied. SWR female mice were crossed with Muta(TM)Mouse males to obtain F(1) progeny for analysis of mutant frequency. At conception, the dams were put into two groups, one that was fed ad libitum and another which was fed 80% of the ad libitum diet. Pups were killed at birth, DNA was extracted from the whole animal and used to measure the mutant frequencies of the mice at the cII locus. Although the weights of the pups from dams whose diet was restricted were significantly less than those of the ad libitum mice (P = 0.003), the litter sizes in the two groups were approximately the same and did not differ significantly (P = 0.13). There was no significant difference in the mutant frequencies in the dietarily restricted and ad libitum groups (P = 0.43). In addition, there was no significant correlation between the weights of the pups and their mutant frequency in either the ad libitum or dietarily restricted groups (r(2) = 0.14 and r(2) = 0.024). No difference was observed in mutant frequency between the ad libitum and dietarily restricted mice from litters of the same size (P = 0.61). These results indicate that the protective effect of dietary restriction on cancer rates is not mediated by an alteration in the spontaneous rate of mutation but rather by another mechanism, such as its effect on induced mutation.