Dominant Lethals Research Articles

Use of compound-probability distributions in the study of induced post-implantation dominant lethals

The nature of the probability distribution of post-implantation dominant lethality was investigated in terms of the distribution of dead implants per female. It has been postulated that this distribution would be poisson in a control series of females but may follow a compound or a contagious distribution such as the beta binomial, negative binomial or Neyman type A in the treated series of females. The nature of these compound distributions for fitting mammalian mutagenicity has been examined. The implications of the results on the estimation of induced mutation rates are discussed.

Techniques for manipulating chromosomal rearrangements and their application to Drosophila melanogaster. I. Pericentric inversions.

Techniques have been developed for manipulating pericentric inversions in Drosophila that are based on the lethality of grossly aneuploid zygotes and the existence of recombinationally interconvertible genotypes for any heterozygous inversion complex: males of some of these genotypes will produce only aneuploid sperm, which can be used to rescue complementary aneuploid ova and selectively recover recombinational derivatives of inversions. Markers can be recombined into inversions through a sequence of selected single exchanges, and a novel type of duplication can be synthesized from overlapping inversions that has the characteristics of both insertional and tandem duplications; there are also applications to half-tetrad analyses.--Two cytogenetic screens are developed: (1) the dominant lethality of a large insertional-tandem duplication can be reverted by deletional events that give rise to net deficiencies or duplications, and (2) deficiencies and tandem duplications in proximal regions can be selectively recovered as the results of unequal exchanges within an inversion loop. Recombinants have been recovered between breakpoints separated by distances of as little as fifty bands, arguing against the existence of some small number of sites necessary for the initiation of recombinational pairing. In several instances, hyperploids for four to six numbered divisions were observed to be fertile in both sexes.

Induction of dominant lethals by fractionated doses of EMS

Induction of dominant lethals by fractionated doses of EMS

Effect of ethidium bromide onDrosophila melanogaster andDrosophila simulans

Ethidium bromide was fed toD. melanogaster andD. simulans males in order to test its toxic capacity and potency for the induction of dominant lethals. Our results show that ethidium bromide has a high toxicity and likewise produces dominant lethals to a significant extent in both species, but more effectively inD. melanogaster.

Mutagenicity of hycanthone in drosophila: Additional results and a comparison with some analogs

The data reported in this paper extend earlier results on the effects of hycanthone in Drosophila. The main findings are the following. (1) A refined brood-pattern analysis of hycanthone-induced sex-linked recessive lethals confirmed the specific sensitivity of mid- and late spermatids. Injection of young males (0–20 h old) did not cause a shift in the brood pattern, but tended to produce higher rates of recessive lethals than injection of 4-day-old males, although the difference was not significant. (2) An autosomal recessive lethal test (chromosome 2) similarly showed a low sensitivity of premeiotic stages. (3) Feeding of hycanthone was much less effective than injection. This difference was not observed for the methyl analog lucanthone. From the observation that hycanthone- and lucanthone-induced mutations exhibited different germ-cell-stage sensitivity patterns, it was concluded that lucanthone does not (at least not exclusively) act via metabolic activation to hycanthone. (4) After injection, the hycanthone analogs IA-4- N-oxide and IA-4- N-oxide were marginally mutagenic. (5) It was shown previously that hycanthone was ineffective in producing breakage events, in Drosophila. In this report, hycanthone is shown to be weakly active in inducing ring-X chromosome loss. This emphasizes the relat ive sensitivity of the ring-X-loss test, in comaprison with the tests that etect translocations or dominant lethals.

The effects of radiation dose-rate and quality on the induction of dominant lethals in mouse spermatids

Hybrid male mice were given 3 Gy (300 rad) doses of X- or γ-irradiation at dose-rates of either 0.6 or 0.002 Gy/min for each radiation. Germ-cells treated as spermatids were tested for dominant lethality. Effects on spermatogonia were evaluated by studying testis-weight, sperm-count and sperm abnormalities. The rate of induction of dominant lethal mutations was 2.1 times as high after acute X-irradiation as after protracted γ-irradiation. Most of this difference resulted from the change in radiation quality, since the relative effectiveness of X- versus γ-irradiation was 1.9 at low at 1.6 at high dose rates. For each radiation, however, fewer dominant lethals were induced at low dose-rates than at high (low/high ratios of 0.8 and 0.9 respectively) although differences did not reach a significant level. There were no statistically significant effects of dose rate on testis-weight or sperm-count in the X-ray series, but there were significantly less severe effects on both with protraction of the γ-irradiation. Evidence for effects of radiation quality on these characters was conflicting. Frequencies of abnormal spermatozoa were markedly increased 7 weeks after irradiation but there were no consistent effects of radiation intensity or quality.

Effect of pollen ultraviolet radiation on the abortion frequency and segregation patterns at various endosperm mutant loci in maize ( Zea mays L.)

Exposure of pollen grains to ultraviolet radiation before pollination is known to produce genetic damage resulting in kernel abortion. However, little or no information is available regarding the effects of radiation on kernel abortion in different genetic backgrounds within a species or the transmission of different alleles at the same locus. To study these aspects, four populations which had the same female parent and were heterozygous at one of four endosperm mutant loci ( waxy, sugary-1, shrunken-2, opaque-2) were used. Fresh, mature pollen grains from each of these heterozygous populations ( Wxwx, Su 1 su 1, Sh 2 sh 2, O 2 o 2) were exposed to seven levels of ultraviolet radiation (254 nm) from 0 to 8.16 × 10 5 erg/cm 2 at 1.36 × 10 5 erg/cm 2 intervals. After exposure, the pollen grains were used to pollinate their source. On each of the resulting ears, the frequency of the partially-aborted (embryo and/or endosperm visibly defective) kernels in the total number of normal (both embryo and endosperm fully-developed in size and appearance) and partially-aborted kernels was determined. The frequency of recessive kernels in the total number of normal kernels was also obtained for each heterozygote. For both the partially-aborted and recessive frequencies, the F values for the main effects, heterozygote and exposure, and their interaction were significant at the 1% level. Over all heterozygotes, the partially-aborted frequency ranged from 0.020 at 0 level to 0.581 at 6.80 × 10 5 erg/cm 2 with a non-significant decrease to 0.577 at 8.16 × 10 5 erg/cm 2. The major increases occurred at the lower and intermediate levels. With increasing exposure, O 2 o 2 showed the largest increase (from 0.022 at 0 level to 0.774 at 8.16 × 10 5 erg/cm 2) in partially-aborted frequency while Su 1 su 1 exhibited the smallest (from 0.010 at 0 level to 0.412 at 8.16 × 10 5 erg/cm 2). Estimates of dominant lethality followed a positive linear pattern with smaller differences present between heterozygotes. Over all heterozygotes, the recessive frequency ranged from 0.237 at 0 level to 0.283 at 6.80 × 10 5 erg/cm 2 with a non-significant decrease to 0.267 at 8.16 × 10 5 erg/cm 2. With increasing exposure, O 2 o 2 showed the greatest increase in the recessive frequency ranging from 0.241 at 0 level to 0.343 at 5.44 × 10 5 erg/cm 2 with a non-significant decrease found above this level. Su 1 su 1 and Sh 2 sh 2 expressed a similar but less pronounced increase in the recessive frequency with increasing exposure while the response of Wxwx was quite erratic. The results indicated that increasing exposure to ultraviolet radiation increased: (1) Partial abortion with the amount dependent on the genetic background of the pollen source; and (2) The transmission of the recessive allele with the amount dependent on the locus.

Nutrient deficiency and the sensitivity of Drosophila melanogaster to an alkylating agent

The lowest dietary concentrations of cholesterol, choline, nicotinic acid, calcium pantothenate, pyridoxine·HCl and riboflavin that yield adult males whose longevity and fertility are sufficient for mutation studies were defined for the Canton-S strain of Drosophila melanogaster. Because the combined physiological indices indicated that the severities of the individual nutritional deficiencies were quantitatively similar, comparisons were made using the summed data for males fed deficient or optimal concentrations of the test nutrients. Compared to the broods of untreated control males, the incidence of unhatched eggs was higher in brood 1 of three 4-day broods and the frequencies of larval and pupal mortality were lower in all three broods derived from two day old untreated males raised on deficient diets. Dietary deficiencies apparently modify sperm function and the expression of paternal genes in the progeny. According to the frequencies of induced dominant lethal mutations, dominant lethals blocking fertilization or embryonic events were more frequent in brood 1 sperm of Trenimon-treated males raised on deficient diets than in brood 1 sperm from control-treated males; however, dominant lethals terminating larval development in brood 1, 2 and 3 progeny and pupal development in brood 1 offspring were more prevalent in the sperm of control-treated males. Lower frequencies of X-chromosomal recessive lethal mutations were found in brood 1 and 2 of deficient Trenimon-treated males than in the corresponding broods of treated-control males. Dietary deficiencies for the test nutrients are proposed to be inhibitory to the repair system that heals the broken chromosomal ends formed by Trenimon in the sperm of males of D. melanogaster.

Investigations on radiosensitive and radioresistant populations of Drosophila melanogaster VIII. The system of relative radioresistance in immature oocytes of the irradiated population [formula omitted

• Prophase I oocytes of the irradiated population R O ̈ I 4 of Drosophila melanogaster are radioresistant relative to those of a control population (+ K). The system of relative radioresistance is apparently dose-modifying and can be described by Dose-Reduction Factors (DRFs). At least 3 contituent components of the system can be distinguised, as follows. • The genetic factor rar-1 contributes to the system with respect to the induction of dominant (DRF = 1.31) and sex-linked recessive lethals (DR = 1.31) in a way that is inhibited by caffeine. • The factor rar-2, independently reduces both types of lethal to the same amount as does rar-1, but also affects the production of X-chromosome loss (DRF = 1.72). The results of several different approaches allow, as a working hypothesis, the interpretation that rar-2 reduces the association of heterologous, chiasmatic chromosomes in the chromocentre in time and/or space and thus minimizes the preconditions for the production of certain types of interchange and of non-disjunction. • A third factor, rar-3, is postulated to contribute, independently from the others, to the system of relative radioresistance with respect to dominant lethals (DRF = 1.58), interchanges and non-disjunction (DRFs = 1.58), and sex-linked recessive lethals (DRF = 1.87).

Studies on chemical induction of chromosomal aberrations in postcopulation germ cells and zygotes of female mice. I. Comparative studies on the frequency of first-cleavage chromosomal aberrations and dominant-lethal mutations.

The correlation between dominant-lethal mutations and chromosome aberrations in first cleavage and the relative sensitivities of germ cells and zygotes to the induction of chromosome aberrations by methyl methanesulfonate (MMS), iso-propyl methanesulfonate (iPMS) and Mitomycin C (MC) were studied in copulated females.All chemicals tested induced dose-dependent dominant-lethal erects. The incidence of dominant lethals induced by postcopulation treatment with MMS was about half of that induced in spermatozoa and late spermatids in males at same dose, whereas the incidence obtained by iPMS or MC treatment was about 7 and 14 times, respectively. The relationship between dominant lethals and chromosome aberrations at first cleavage was not necessarily direct, which was suggestive of the involvement of some non-genetic erects. Chromosome aberrations observed in first cleavage were very high in preovulatory oocytes and sperm in oviducts (immediately after copulation) by MMS or MC treatment. iPMS, on the other hand, did not induce so many aberrations as MMS or MC did. In the case of MMS, the number of structural aberrations in the paternal chromosomes was greater than in maternals, but the extent of aberrations induced by MC or iPMS could not be distinguished because of the chemical-induced delay of pronuclei to develop.

A comparison of the molecular action of an S N1-type methylating agent, methyl nitrosourea and an S N2-type methylating agent, methyl methanesulfonate, in the germ cells of male mice

A study has been made of the unscheduled DNA synthesis (UDS) induced in early spermatid stages of the mouse by methyl nitrosourea (MNU), a methylating agent that reacts predominantly by an S N 1 type mechanism. In comparison with methyl methanesulfonate (MMS), a methylating agent that reacts predominantly by an S N 2 mechanism, MNU induced more UDS by a factor of about 1.4. This result was in line with chemical dosimetry studies carried out with both chemicals, which showed that 4 h after treatment with MNU, testicular DNA was methylated about 1.5 times more than it was 4 h after treatment with MMS. The UDS response in the spermatids fell off rapidly in the first half-day after treatment with either MNU or MMS. However, from 0.5 to 3 days after treatment the UDS response decreased with a t 1 2 of 2.4 days after MNU treatment, but 1.2 days after MMS treatment. Chemical dosimetry studies with 3H-labeled MNU and MMS showed that the pattern of methylation produced in the developing sperm was different for each chemical and was generally correlated with the corresponding pattern of induced dominant-lethal mutations. However, on the basis of equal sperm-head methylation, MNU is as much as 17 times more effective than MMS in producing dominant lethals. It is suggested that more methylation by MNU at the O-6 position of guanine or phosphate groups in DNA in the developing germ cells may account for MNU's greater effectiveness in inducing dominant lethals. Greater methylation of these sites by MNU than by MMS might also account for the differences observed in the UDS response of the spermatids to these chemicals.

Dominant lethality in Xenopus laevis induced with triethylenemelamine (TEM).

Adult male South African clawed toads, Xenopus laevis, were injected intraperitoneally with triethylenemelamine (TEM) dissolved in water over a dose range of 13-1,300 micrograms/kg or with water (controls). Mating of the treated males with untreated females was induced seven days later by injection of human chorionic gonadotropic hormone (HCG). Accumulated lethality one week after fertilization among progeny was dose related. Morphological abnormalities among embryos that survived to hatching were similarly dose related. Because anatomically anomalous embryos may have impaired behavior, swimming capacity was tested, and anomalies in swimming behavior were also found to be dose related. Finally, short-term cell cultures were made on minced embryos to obtain chromosome spreads. Structural aberrations, rings, dicentrics, etc of somatic chromosomes were also dose related.

Parametric statistical methods and sample size considerations for dominant lethal experiments: The use of clustering to achieve approximate normality

AbstractWhile the dominant lethal (DL) assay is often used to assess the mutagenic potential of suspect agents, questions remain concerning its sensitivity, the appropriate way to analyze resultant data, and the necessary study size. Many questions surrounding the statistical analysis methods relate to a specification of the basic independent unit of experimentation and analysis, the particular type of study design used, and the distributional properties of the study variables. These statistical analysis issues must be resolved before adequate attention can be given to the related questions of experimental sensitivity and sample size. This report deals with the development of a statistical analysis methodology which incorporates a particular type of data clustering scheme to achieve desirable distributional properties of the measured variables so that analysis of variance (AOV) and related parametric testing procedures can be used. Further, the differences between dose groups which can be detected using 20, 10, and 5 cluster units of 6 males and 18 females each are estimated for each variable according to the size of selected Type I and II errors. While these procedures were developed in part using data from two replicate studies on the DL effects of differing doses of n‐butyl glycidyl ether in mice, the clustering scheme suggested can be used with other AOV and regression procedures corresponding to the specific study design employed.

Long-term feeding studies in mice fed a diet containing irradiated fish I. Multigeneration reproduction, mutagenicity, teratology, and longevity studies

A wholesomeness feeding study was carried out in mice fed equal amounts of cod or redfish, comprising 45% of the diet. Three groups of animals received either irradiated [1.75 kGy (175 krad)] fish, non-irradiated fish or stock ration. A 90-day subchronic study,a multigeneration reproduction, a dominant lethality and a teratology study were carried out together with an 80-week oncogenic study on the F 1 generation. No adverse effects were noted on growth, reproduction and litter behaviour, in relation to dominant lethality, teratogenicty or oncogenicity.

The mutagenic effect of Trifluralin-containing herbicide on mouse germ cells in vivo

The mutagenic effect of the 26% Trifluralin-containing herbicide Olitref on mouse germ cells was investigated using three test methods: (a) spermatocyte chromosome examination; (b) dominant lethality test; and (c) F 1-embryonic chromosome examination. One-third (0.20 g/kg) of the LD 50 of Olitref was found mutagenic in the applied test. When a single dose of one-hundredth (0.006 g/kg) of the LD 50 was injected in the spermatocyte examination, mutagenic change was also observed, but the results were only on the border of significance.

Response of mutagen-sensitive Drosophila melanogaster to hyperthermia and radiation

In an attempt to understand the mechanism of hyperthermia sensitization of radiation-induced damage, males of 5 mutant mutagen-sensitive strains: mei-41 A1, w mus(1)101 D1, w mus(1)104 D1, y mei-9 a, and w mus(1)102 D2, representing at least 3 different defects in the DNA-repair pathways were exposed to hyperthermia (38°C for 1 h) and to 1000 R of X-rays. In all of the mutagen-sensitive strains, the radiation-induced dominant lethals were enhanced by the hyperthermia treatment in the 6–8 day brood, which included the meiotic division at the time of radiation, and in the postmeiotic broods. The radiation-induced recessive lethals were also significantly increased by hyperthermia treatment in all the mutagen-sensitive mutants except mei-41 A1 in 4–6 day brood. However, mei-41 A1 males produced a significant increase of lethals in earlier broods, 0–2 and 2–4 day. The hyperthermia which apparently sensitizes radiation-induced damage by inhibiting DNA and probably chromosome-repair systems, is not specific, at least for 3 different Drosophila repair pathways.

Whole-mammal mutagenicity tests: Evaluation of five methods

Transmitted genetic changes in mammals can be used to study all of the main endpoints of mutagenesis: point mutations, chromosome breakage, with or without rearrangement, and chromosome nondisjunction. Four methods most commonly employed in whole-mammal germ-line mutagenicity tests as well as an in vivo somatic prescreen, are summarized. Genetic basis, historical background, description of the test, limitations, and strengths are presented for each of the five systems. The specific-locus test using visible markers is the most reliable and practical method for detecting heritable point mutations, including small deficiencies, and does not require very large numbers of animals for risk extrapolations, if a relatively high dose can be administered without killing germ cells. For the detection of chromosome-breakage events, dominant lethals are useful to determine relative sensitivities of different germ-cell stages of the male, but the heritable-translocation test is more sensitive when the exposed cells are male meiotic and postmeiotic stages. Chromosome breakage events in the female are best revealed through a sex-chromosome loss test, which utilizes genetically marked X chromosomes. The same method can also be employed to detect nondisjunction in either sex. The in vivo somatic mutation test is useful as a prescreen for both point mutations and losses of chromosomal material. The reliability and efficiency of whole-mammal mutagenicity tests must be considered in two contexts: in the assessment of mutagenicity per se (as this applies to genetic changes transmitted to future generations), and in the use of mutagenicity as a possible indicator of carcinogenicity. In the former context, the whole-mammal tests are irreplaceable because they provide the closest practicable approach to the metabolic pathways existing in man, and because there is no array of lower-system tests that can predict the complexity of the response of the different mammalian germ-cell stages (which differ greatly with respect both to their absolute and their relative sensitivities to the induction of various genetic endpoints). In the second context, i.e., the use of mutagenicity as a screen for carcinogenicity in the exposed individual, most of the whole-mammal tests are of more limited utility, because they require several weeks or months for completion. Of the methods discussed, the spot test appears most suitable, because it provides a relatively rapid in vivo system capable of detecting both gene mutations and chromosomal changes of various kinds in somatic cells, including some that have been suggested to be involved in tumor promotion.

Toxicity, fertility, teratogenicity, and dominant lethal tests in rats administered cadmium subchronically: II. Fertility, teratogenicity, and dominant lethal tests

Four groups of Sprague-Dawley rats, each of which consisted of 14 males and 14 females, were administered 0, 0.1, 1.0, and 10.0 mg/kg/day of cadmium (Cd) for 6 weeks. Males and females within each group were mated 6 days a week for 3 weeks, changing partners every week if necessary. Cd was administered during the mating period. Pregnant females were administered Cd during the gestation period and killed on the 20th day of gestation for teratogenicity tests. Males were mated with 2 virgin females per male per week for 6 weeks. Pregnant females were killed on the 13th day of gestation for dominant lethal tests. Numbers of total implants and live fetuses in the 1.0 mg/kg group decreased slightly, but there was no significant difference from the control. Numbers of total implantations and live fetuses decreased significantly in the 10.0 mg/kg group. In this group, the number of resorbed fetuses increased significantly and the number of corpora lutea decreased without showing a significant difference from the control. Fetuses from the 10.0 mg/kg group showed decreased body weight, body length, and tail length and increased placental weight. About one-third of fetuses were subjected to visceral examination, but no specific anomalies considered to be due to Cd toxicity were found. Skeletal examination was performed for the remaining two-thirds of the fetuses. Delayed ossification of the sternebrae and caudal vertebrae was observed. No dominant lethality was found under the conditions used here. Although physiological deterioration caused by 10.0 mg/kg of Cd has an adverse effect on mating performance, mating ratio, the number of total implants, the number of live fetuses, and the ossification of fetuses, Cd induced neither teratogenicity nor dominant lethality.

Toxicity, fertility, teratogenicity, and dominant lethal tests in rats administered cadmium subchronically: I. Toxicity studies

In order to obtain an overall understanding of the toxicity of cadmium (Cd), a single experimental series was designed to investigate the diverse effects of Cd. Four groups of Sprague-Dawley rats, each of which consisted of 14 male and 14 female rats, were administered Cd (CdCl 2) orally at dose levels of 0, 0.1, 1.0, 10.0 mg/kg/day for 6 weeks. After this, the animals were mated for 3 weeks, changing partners every week, for fertility and teratogenicity tests. Cd was given during this mating period. Females were administered Cd during gestation and sacrificed on the 20th day of gestation for fetal examination. After a total of 9 weeks administration, males were subjected to dominant lethal tests by mating 2 females per male per week for 6 weeks. Pregnant females were killed on the 13th day of gestation to test for dominant lethality. This paper reports the results of the general toxicity tests. The main toxic signs, seen only in the 10 mg/kg group, were repression of food intake and body weight gain, depilation, whitening of the incisors, and salivation. Hematological analyses showed that the number of RBC increased while hemoglobin and hematocrit levels decreased, and the number of WBC increased, mainly as a result of neutrophilia. Serum biochemical analyses indicated increased levels of GPT and creatinine, reflecting damage to the liver and kidneys. Increased glucose levels were seen in males. A major change found at the time of autopsy by macroscopic observation of organs was hypertrophy of the jejunum and ileum with a darkish-brown color in nonpregnant females of the 10 mg/kg group. Microscopically, hyperplasia with a high frequency of mitotic figures was seen in the lamina propria mucosae. The weight of the thymus decreased and the weight of the adrenals increased in both males and females. The weight of the ovaries decreased. Major histopathological changes were focal necrosis in the liver and hyperplasia of the adrenal cortices with patchy necrosis in nonpregnant females of the 10.0 mg/kg group. Determination of Cd in the liver and kidneys suggested that excretion of the accumulated Cd was slow. Two aspects of Cd toxicity, i.e., the inhibition of nutrient resorption by unresorbed Cd and the toxicity expressed by resorbed Cd, as well as the causative factors of the adrenal hyperplasia, are discussed.

Preliminary studies on the toxicity and mutagenicity of 1-amino-2-naphthol-4-sulphonic acid inDrosophila melanogaster

The toxicity and mutagenicity of 1-amino-2-naphtho-4-sulphonic acid were analysed inDrosphila melanogaster. Rate of development and viability were the two parameters employed to study the toxicity. The frequency of dominant lethals was scored to evaluate the mutagenic effect of the chemical on male and female germ cells. Concentrations of 250 mg and above/100 ml wheat cream agar medium were found to be significantly toxic. Significant number of dominant lethals was induced even by a concentration as low as 50 mg/100 ml medium. Male germ cells were more sensitive than female germ cells.