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The results of the genetic, cytogenetic and molecular analysis of the recessive mutations at the small, lying close to the centromere, cinnabar (cn) gene of Drosophila melanogaster induced by γ-rays of 60Co (doses 5-60 Gy) or 0.85 MeV fission neutrons (doses 2.5-20 Gy) in the mature sperm of the wild-type males from the laboratory line D32 are presented. The whole spectrum of the cn mutations induced by different quality radiation is found to be the same and consists of the two main-distinct classes such as gene/point and gene/chromosome mutations either of which includes the array of the subclasses (gene/point simple or complex mutations and chromosome rearrangements detected as F1 cn mutants with dominant sterility of multilocus deletions involving the cn gene wholly). The induction rate of both mutation classes is found to be increased linearly with dose of low- and high-LET radiation and the RGE values of neutrons are 1.0 and 4.0 for the gene/point and gene/chromosome mutations respectively. According to the data of the molecular analysis, 28 out of 59 (47.5%) γ-ray- and neutron-induced gene/point cn mutations studied are found to have the intragenic DNA alterations detected by PCR technique as a loss of the single or two adjacent fragments-amplicons non-randomly located at the 5'- or 3'- end of the gene map. Essentially, 10 out of 48 (20.8%) γ-ray-and 3 out of 11 (27.3%) neutron-induced gene/point mutations are found to show the same molecular "phenotype" (the loss of the two adjacent fragments at the 3'- end of the gene map) as that in the cn1 allele-marker from the maternal tester-line KL with the females of which the irradiated males were crossed. Among the putative recombination-based genetic processes underlying the exchange between the cn1 and damaged cn(+32) alleles, the gene conversion in the "gonomeric" nucleus of the zygote seems to be the most likely such processing. The established features of the cn gene radiomutability are compared with those earlier described for the other small gene black+ located in the middle of the 2L chromosome.

To determine whether the linear no-threshold (LNT) model for stochastic effects of ionizing radiation is applicable to very low-dose radiation at a low dose rate, we irradiated immature male germ cells of the fruit fly, Drosophila melanogaster, with several doses of (60)Co gamma rays at a dose rate of 22.4 mGy/h. Thereafter, we performed the sex-linked recessive lethal mutation assay by mating the irradiated males with nonirradiated females. The mutation frequency in the group irradiated with 500 microGy was found to be significantly lower than that in the control group (P < 0.01), whereas in the group subjected to 10 Gy irradiation, the mutation frequency was significantly higher than that in the control group (P < 0.03). A J-shaped dose-response relationship was evident. Molecular experiments using DNA microarray and quantitative reverse transcription PCR indicated that several genes known to be expressed in response to heat or chemical stress and grim, a positive regulator of apoptosis, were up-regulated immediately after irradiation with 500 microGy. The involvement of an apoptosis function in the non-linear dose-response relationship was suggested.

The frequency of irradiation-induced recessive lethals has been studied in chromosomes 1 and 2 of Drosophila melanogaster. It supposed, that the higher level of mutability may be explained in destabilization of genotype. The essential part in induction of genotype destabilization replies the genome instability mechanisms.

Loss of heterozygosity (LOH) is a frequent event in many tumours, resulting in the loss of tumour suppressor genes and ultimately magnifying the number of cells with a mutant phenotype. We have used the Dlb-1 locus as a simple quantitative assay for LOH in vivo. Mutations of the dominant Dlb-1b allele are readily detected in heterozygous (Dlb-1a/Dlb-1b) mice by the loss of histochemical staining, which results in unstained, white (Dlb-1a/Dlb-1-) ribbons on a stained background. Such ribbons are extremely rare in untreated C57BL mice which are homozygous for the dominant allele, as would be expected when two independent mutations are required. To test for LOH, we first treated the animals with a high dose of ethylnitrosourea (ENU) which induces many mutations and thus many heterozygous cells, and allowed 2 weeks for gene expression. Then the animals were treated with the test agent to determine if it could cause LOH and thus convert heterozygous mutant cells, which would not produce detectable ribbons, into homozygotes that would produce white, non-staining ribbons. Treatment with ENU alone produced a low, but detectable, frequency of mutant ribbons. Treatment with X-rays alone produced no detectable increase in the frequency of mutant ribbons. Combinations of these treatments produced additive effects, thus showing that no significant LOH was induced. The additivity of the two equal ENU treatments was unexpected, since double mutants should increase as the square of the mutant frequency.(ABSTRACT TRUNCATED AT 250 WORDS)

Male mice of the genotypes AKR, BALB/c, (102/ElxC3H/El)F1 or DBA/2 were exposed to 3 + 3 Gy irradiation with a 24 h fractionation interval and mated to untreated Test-stock females. The offspring were screened for activity alterations of 10 erythrocyte enzymes as well as recessive specific-locus and dominant cataract mutations. The observed mutation rates per locus per gamete x 10(-5) for treated spermatogonia were 6.8, 4.9, 2.5 and 1.3 for enzyme-activity mutations, 8.6, 24.1, 22.8 and 31.4 for specific-locus mutations, and 0.7, 0.9, 0.6 and 2.5 for cataract mutations, respectively. Some variability from strain to strain in the frequency of radiation-induced mutations was observed. However, there was no consistent effect of genotype on the frequency of induced mutations and it is concluded that no effect of genetic background exists for the four genotypes tested. There is good agreement between the observed enzyme-activity mutation rate in children of survivors of the atomic bombings and the expected mutation rate based on results with mice. Results are therefore consistent with an estimation of human radiation-induced genetic risks based upon an extrapolation of experimental results in the mouse.

In experiments with C57BL/KsJY mice carrying a mutant db gene at the heterozygous and homozygous states it has been found that db+/+db mice are much more sensitive to gamma radiation with respect to the survival rate. In homozygotes, in contrast to heterozygotes, irradiation with a dose of 6 Gy does not reduce the severity of the diabetogenic effect of low doses of streptozotocin.

Two groups of lethal mutations that are expressed only in somatic cells were isolated using the gonosomic selective method. The mutations tend to be organized in clusters along the sex chromosome. Analysis of mutation expression allowed to characterize the degree of changes in genetic diversity of somatic and germ lines in development; it is minimal in the III instar larvae and prepupae and maximal in the I and II instar larvae and pupae.

The dilute (d) coat color locus of mouse chromosome 9 has been identified by more than 200 spontaneous and mutagen-induced recessive mutations. With the advent of molecular probes for this locus, the molecular lesion associated with different dilute alleles can be recognized and precisely defined. In this study, two dilute mutations, dilute-lethal20J (dl20J) and dilute prenatal lethal Aa2, have been examined. Using a dilute locus genomic probe in Southern blot analysis, we detected unique restriction fragments in dl20J and Aa2 DNA. Subsequent analysis of these fragments showed that they represented deletion breakpoint fusion fragments. DNA sequence analysis of each mutation-associated deletion breakpoint fusion fragment suggests that both genomic deletions were generated by nonhomologous recombination events. The spontaneous dl20J mutation is caused by an interstitial deletion that removes a single coding exon of the dilute gene. The correlation between this discrete deletion and the expression of all dilute-associated phenotypes in dl20J homozygotes defines the dl20J mutation as a functional null allele of the dilute gene. The radiation-induced Aa2 allele is a multilocus deletion that, by complementation analysis, affects both the dilute locus and the proximal prenatal lethal-3 (pl-3) functional unit. Molecular analysis of the Aa2 deletion breakpoint fusion fragment has provided access to a previously undefined gene proximal to d. Initial characterization of this new gene suggests that it may represent the genetically defined pl-3 functional unit.

A method of selective screening of recessive sex-linked lethal mutations, that are manifested only in somatic cells of D. melanogaster, has been developed. Lethals were induced with X-irradiation of X-chromosomes at the moment of their topographic segregation from embryonic somatic cells. Analysis of mutation expression confirmed the method selectivity.

A simple procedure for induction of nistatin-resistant mutants in yeasts under the action of 6-N-hydroxylaminopurine (HAP) is proposed. Some differences between the spectra of mutations induced by HAP and UV-light are observed: HAP induces dominant and double recessive mutants more frequently.

The mutagenicities of malondialdehyde and formaldehyde were tested by screening each for genetic mosaics of Drosophila melanogaster and by the Muller-5 test for sex-linked recessive lethal mutations. For comparison, the effects of X-rays were also assayed by the above technique. Malondialdehyde, a degradation product of polyunsaturated fatty acids, was found to be a weak mutagen by the above criteria; it induced point mutations and chromosome exchanges at low frequency, as proved by the mosaic test, but failed to induce detectable sex-linked lethality. Formaldehyde was more mutagenic than malondialdehyde; beside induction of mosaic spots it induced sex-linked recessive lethal mutations, but only in the larval testes of Drosophila. Formaldehyde also induced disintegration of the clones. Formaldehyde treatment (feeding larvae with formaldehyde-containing food for about 4 days) was 5 times more mutagenic than malondialdehyde treatment and 5 times less effective than irradiation by 1000 R of X-rays. Wing mosaicism offers a more sensitive way to detect mutagenesis as compared with eye mosaicism. It is suggested that aldehyde-induced mosaic spots derive from mitotic recombination and point mutations.

Risks of serious hereditary damage in the first and second generations after low level radiation exposure and at equilibrium were calculated by using a doubling dose of 100 rem (based on experimental work with the mouse) and by considering separately the various categories of genic and chromosomal defect. Prenatal lethality has not been included. It is estimated that after the exposure of a population of future parents to a collective dose of 1 million man-rem, about 125 extra cases of serious genetic ill health would appear in children and grandchildren. In all future generations, a total of about 320 cases is expected, provided the population remains of constant size. It is emphasised, however, that a number of major assumptions have to be made in order to arrive at any overall genetic risk estimate, so that the confidence limits of these figures are bound to be wide.

The frequencies of spontaneous and ethylmethanesulfonate and X-ray-induced mutations in III chromosome of strains D-32 (wild type) and mei-9LI deficient in excision repair have been studied. Mutations have been induced in mature spermatozoa and analysed using multiply marked strain rucuca. It has been shown that the spectra of mutability and frequencies of mutations don't differ in both strains. It indicates the absence of specificity of mutagens studied.

The radiation-resistant free-living nematode Panagrellus redivivus was used to study mutation rates in oocytes, following gamma, proton and neutron irradiation in the dose range 45-225 grays. gamma-Radiation produced approximately 0.001 lethal X-chromosomes per gray over the range tested. Proton or neutron irradiation produced approximately 0.003 lethal X-chromosomes per gray at lower doses, with the mutation rate dropping to 0.001 lethal X-chromosome per gray at the higher doses. These results suggest a dose-dependent mutation-repair system. Cell lethality was also examined. gamma-Radiation produced the greatest amount of cell lethality at all doses, while neutron irradiation had no cell lethal effect at any of the doses examined.

The effect of material repair on induction of paternal mutations was tested with radiosensitive rad(2)201G1 mutant. Basc males were irradiated at doses from 0 to 60 Gy of gamma-rays and mated to the radiosensitive mutant or control females. Frequencies of sex-linked recessive lethals and dominant lethals (induced in the paternal genome) were determined. With control females, the rate of recessive lethals increased linearly from 0 to 60 Gy. With rad(2)201G1 mutant, an increase in spontaneous and induced rates of paternal dominant lethals was observed; the rate of sex-linked recessive lethals increased non-linearly from 0 to 60 Gy.

To determine the mechanism by which the recessive Fv-2r gene confers complete resistance to spleen focus formation and to the induction of early splenomegaly characteristic of the Friend virus (FV) disease syndrome, we compared the parameters of FV infection in susceptible DBA/2 (D2) (Fv-1n, Fv-2s) and partially congenic D2.Fv-2r (Fv-1n, Fv-2r) mice. After infecting these mice with N-tropic FV complex, we followed the replication of spleen focus-forming virus (SFFV) and the generation of SFFV-transformed tumor colony-forming cells (CFC) in their spleens. By both parameters D2.Fv-2r mice were 20- to 100-fold less susceptible than DBA/2 controls, but the inhibition was only partial. Transplantation of washed spleen cells from SFFV-infected DBA/2 mice resulted in equal growth and recovery of tumor CFC from both D2.Fv-2r and Fv-2s mice. However, these tumor cells grew as colonies in Fv-2s mice, whereas they grew diffusely in the spleens of D2.Fv-2r hosts and did not develop into macroscopically or microscopically visible colonies. Thus the completeness of the resistance to spleen focus formation that defines the Fv-2r gene was reflected only in the complete suppression of the colonial growth of tumor cells, whereas the other parameters of infection showed no or only partial inhibition.

Recessive mutations only occurring in two genes (ribosomal suppressors sup1 and sup2) can be obtained using special selective system. We demonstrate that the absolute selectivity of the system is based on selection for simultaneous reversions to prototrophy in mutants requiring adenine and histidine in haploids marked by two different nonsense mutations--his7-1 (UAA) and ade1-14 (UGA, this being identified in the present study). In support to this conclusion, we developed an analogous system utilising his7-1 (UAA) and lys2-87 (UGA). The selectivity of the system is shown to be influenced both by the choice of nonsense alleles and by genotypic background.

Thirty-four independent nonviable c-locus mutations (types cal, albino lethal and cas, albino subvital), derived from radiation experiments, were tested for involvement of nearby markers tp, Mod-2, sh-1, and Hbb: 10, 22, and 2 involved, respectively, none of these markers, Mod-2 alone, and Mod-2 plus sh-1. When classified on this basis, as well as according to developmental stage at which homozygotes die, and by limited complementation results, the 34 independent mutations fell into 12 groups. From results of a full-scale complementation grid of all 435 possible crosses among 30 of the mutations, we were able to postulate an alignment of eight functional units by which the 12 groups fit a linear pattern. Abnormal phenotypes utilized in the complementation study were deaths at various stages of prenatal or postnatal development, body weight, and reduction or absence of various enzymes. Some of these phenotypes can be separated by complementation e.g., there is no evidence that mitochondrial malic enzyme influences survival at any age); others cannot thus be separated (e.g., glucose-6-phosphatase deficiency and neonatal death).--We conclude that all of the nonviable albino mutations are deficiencies overlapping at c, and ranging in size from less than 2cM to 6-11 cM. The characterization of this array of deficiencies should provide useful tools for gene-dosage studies, recombinant-DNA fine-structure analyses, etc. Since many of the combinations of lethals produce viable albino animals that resemble the standard c/c type, we conclude (a) that the c locus contains no sites essential for survival, and (b) that viable nonalbino c-locus mutations (cxv) are the result of mutations within the c cistron. Viable albinos (cav, the majority of radiation-induced c-locus mutations) may be intracistronic mutations or very small deficiencies.

The frequencies of spontaneous and UV-induced recessive lethal mutations were compared for UV-sensitive and wild-type heterokaryons of Neurospora crassa. These heterokaryons were homokaryotic either for one of two alleles of uvs-3, or for uvs-6 or uvs+. For uvs-3, which is known to have mutator effects, spontaneous recessive lethals were found to be 4-6 times more frequent than observed in uvs+. After correction for clonal distribution of spontaneous mutants, an observed 2-fold increase for uvs-6 was not statistically significant and may have been due to chance occurrence of a few large clones of mutants. Treatment with low doses of UV (50-200 J/m2) produced very similar overall rates of increase for recessive lethals in uvs and uvs+ heterokaryons. This means, that in contrast to results obtained when mutation to ad-3 was measured, both uvs-3 alleles showed highly significant increases for recessive lethals when treated with UV. It is proposed that certain types of UV damage may be processed into recessive lethal mutations by an alternate mechanism from that responsible for viable mutations.

There are no precise data for determining the extent of somatic damage from small doses of radiation used in diagnostic radiology. Diagnostic radiation given to pregnant women, knowingly or unknowingly, should rarely reach teratogenic levels causing brain and eye abnormalities. Evidence suggests that it does increase the risk of childhood malignancy, especially leukemia. Although rapidly growing tissues seem most susceptible, all radiation probably carries a very small risk of carcinogenesis. Genetic damage is equally difficult to estimate. Diagnostic radiation of females, even in childhood, may be related to an increased incidence of Down's syndrome in older mothers. Radiation also causes point mutations, which may explain the increase of some genetic abnormalities in progeny of older fathers. Whenever an abdominal or pelvic radiograph is ordered before the end of the reproductive period, there must be a potential benefit to balance the small risk involved.

The combined effect of X-irradiation and transposon mobility on the frequencies of X-linked recessive lethals and dominant lethals was investigated in female hybrids in the P-M system of hybrid dysgenesis. X-linked lethals were measured in G2 hybrid dysgenic females whose X chromosome was derived from the M X P cross. To test for additivity or synergism, the mutation rate in irradiated dysgenic females was compared to that of unirradiated females as well as to irradiated nondysgenic hybrid females derived from M X M crosses. Eggs collected for 2 days after irradiation, were represented by the more radiation-sensitive A and B oocytes (about 75%) and the least sensitive C oocytes (about 25%). The production of X-linked lethal events in X-irradiated dysgenic females was 8.1%, as compared to 4.5% in dysgenic controls and 3.4% in irradiated, nondysgenic controls, demonstrating an additive effect of radiation and dysgenesis-induced genetic damage. The effect of irradiation on sterility of dysgenic hybrid females was a negative one, resulting in 20% less sterility than expected from an additive effect. The combined effect of radiation and dysgenesis on dominant lethality tested in A, B and C oocytes of the same hybrid females was synergistic. Egg broods collected for 3.5 days after irradiation showed that significantly more damage was induced in the presence of ionizing radiation in dysgenic females than in their nondysgenic counterparts. This effect was most obvious in B and C oocytes. The synergism observed may be related to the inability of cells to repair the increased number of chromosome breaks induced both by radiation and transposon mobility.

The sensitivity to gamma-rays of a hyperkinetic mutant (HK1), characterized by high metabolic activity, has been studied and compared with gamma-ray sensitivity of the wild-type Oregon-K. Radiation damage, as measured by the frequency of induced dominant lethals (DL) and sex-linked recessive lethals (SLRL), was more in HK1 as compared with Or-K. The maximal sensitivity differences for these parameters were observed in the first brood. Translocations, on the contrary, were in general fewer in the HK1 compared with Or-K. These results have been interpreted in terms of reduced repair of mutational lesions in the energy-stressed cells of KH1.

Genetic and molecular analyses of mutations are increasing the qualitative capabilities of the specific-locus test (SLT). Some mutations are found to be deletions of large numbers of genes, including some that control survival at various developmental stages, neurological functions, enzyme syntheses, etc. Smaller (including possibly single-gene) deletions are also detected. A third group of SLT mutations represents intragenic lesions. -- For at least three of the loci, mutations may now be qualitatively grouped on the basis of simple phenotypic findings. Type of mutagen and germ-cell stage exposed strongly influence the nature of the lesions. The qualitative information from SLT results makes possible conclusions about relative potential harmfulness of different types of exposures that may yield equal mutation rates, about differences between induced and spontaneous mutations, etc. It also identifies genetic material suitable for basic studies.

Specific-locus mutation frequencies in mouse stem-cell spermatogonia were determined in 3 experiments in which mature male mice were exposed to 100,m 300, or 500 R of X-rays followed, 24 h later, by intraperitoneal injection of 100 mg/kg of ethylnitrosourea (ENU). The purpose was to find out if the mutation frequencies would be augmented over those expected on the basis of additivity of the effects of the separate treatments. Such augmentation had been observed in earlier work in which exposure to 100 or 500 R of X-rays was followed 24 h later by a second exposure of 500 R. No augmentation was observed for X-rays followed by ENU. The mutation frequencies in all 3 experiments actually fell below those expected on the basis of additivity, although the reductions were not statistically significant.

The recessive visible mutations spectrum of chromosome II induced by X-rays and ethylmethanesulfonata (EMS) in mature Drosophila melanogaster spermatozoa has been studied. Treatment of both mutagens resulted in mutations in all 5 genes in stock mei-9LI and only 4--in D-32. The comparison of mutation frequencies of the same genes in two stocks under EMS-treatment demonstrated the statistical difference of mutation frequencies j, pr, cn of two stocks, genes b and vg did not differ. Under the influence of X-rays the differencies have been observed only for gene b. In stock D-32 the mutation frequency differes from the control for b and vg (EMS treatment) and j, pr, vg (under the action of X-rays), in mei-9LI--the mutation frequency of all 5 genes (under the X-rays) and 4 of 5 genes (EMS treatment).

The character of segregation in diploid gynogenetic progenies of Cyprinus carpio with respect to the following three external characters was studied: the type of scale cover, the colour and the design. The genetic formulae of these characters are as follows: the type of scale cover: scaled--(Snn); scattered--(ssnn); linear--(S--Nn); nude--(ssNn); the existence of design (D--); the absence of design--(dd); the type of colour: light--(LI); dark--(II). The dominant genes N and L exert a recessive lethal effect. For the loci N--n, D--d and L--l a conspicuous prevalence of dominant form was established. Linear and nude carps constituted 98%, light carps--85% and carps with a design--also 85% of the total number of gynogenetic descendants. The proportions of heterozygotes Nn, Ll and Dd were 97.3, 73.9 and 70.0% respectively. The frequencies of descendants dominant and recessive for the locus S--s proved to be closely similar: 52.4% (S--) and 47.6% (ss)the proportion of heterozygotes Ss being 4.8%. The data on the frequency of gynogenetic heterozygotes suggest the existence of a high positive interference in the carp. The value of the latter for the four loci studied, the genetic distance between each of these loci and "its" centromere was determined. The data obtained are discussed.