bluuebunny/crossref_metadata_2025 huggingface dataset:
DNA syntheses in course of meiotic development in Neurospora crassa
Authors: Iyengar G. A. S. , Deka P. C. , Kundu S. C. , Sen S. K.
Published: September 2009

Nuclear DNA syntheses have been measured microspectrophotometrically in course of meiotic nuclear development inNeurospora crassa. The purpose of the study has been to establish the timing of these DNA syntheses in relation to meiosis and in the formation of its final products in an ideal genetic material, where the products of the meiotic division can be recovered and identified. Spectrophotometric analysis has indicated that the last premeiotic DNA replication is completed before caryogamy; a postmeiotic DNA replication takes place at the tetrad of the nuclei level; and finally a second postmeiotic DNA replication occurs in the ascospores to result in eight binucleated ascospores. The timing of postmeiotic replication is compatible with the models explaining gene conversion through the postulated mechanisms involving heteroduplex formation.
Genetic analysis of a cross between two homothallic strains ofPhysarum polycephalum
Authors: Poulter R. T. M. , Honey N. K.
Published: September 2009

The homothallic amoebal clones ofPhysarum polycephalumare of potential use in understanding the developmental genetics of this organism. Such an application requires that complementation and recombination analysis be possible between pairs of homothallic clones. This paper is a report of the formation of mixed plasmodia by pairs of homothallic amoebal clones. In order to detect such mixed plasmodia use was made of two marker genes involved in plasmodial fusion,fusA andfusB. Sporulation of a mixed plasmodium formed from two homothallic (delayed) amoebal clones yielded progeny amoebae which were genetically recombinant. It is deduced from the ratios of various genotypes in these progeny clones that the mixed plasmodium was diploid and that meiosis was associated with sporulation. There is therefore no impediment to the use of the homothallic strains for genetical analysis. The progeny amoebal clones were observed to be showing segregation for the characters homothallic (rapid) and homothallic (delayed). This observation, taken together with other related observations, suggests that the homothallic (delayed) character is produced by mutation of the homothallic (rapid) character. The rare plasmodia formed by a homothallic (delayed) amoebal clone are the result of reversion of this mutation. Amoebal clones of the homothallic (delayed) type are therefore developmental mutants unable to perform the differentiation from amoeba to plasmodium.
Selection for conditional lethals: A general negative selective system for Schizophyllum commune
Authors: Anderson Miriam Rich , Deppe Carol S.
Published: September 2009

This paper describes a method for selecting for conditional lethal mutations in the filamentous fungus Schizophyllum commune. The method is, to our knowledge, the only successful application of filtration enrichment to Basidiomycetes. In addition, it is far more powerful than filtration enrichment methods reported previously for any fungus; it permits recovery of up to 80% auxotrophs starting with material untreated with any mutagen.
Some bryozoan karyotypes and chromosome numbers
Authors: Backus B. T.
Published: September 2009

A technique for obtaining bryozoan chromosome spreads is described. Karyotypes were prepared for the following phylactolaemate species: Plumatella emarginata, 2n = 14; Hyalinella punctata, 2n = 14; Fredericella sultana, 2n = 14; and Pectinatella magnifica, 2n = 18. Approximate numbers were obtained for Lophopodella carteri, 2n 18–22, and three ctenostomes, Pottsiella erecta, 2n = 22 or 24; Amathia semiconvoluta, 2n about 30; and Paludicella articulata, 2n about 20. Differences between the bryozoan karyotypes seen in this study correlate with taxonomy.
The correlation of rare alleles with heterozygosity: determination of the correlation for the neutral models
Authors: Eanes Walter F. , Koehn Richard K.
Published: September 2009

We have shown in an earlier paper that there is routinely a large correlation between the heterozygosity of common (P> 0·05) alleles and the number of rare (P≤ 0·05) alleles at allozyme loci inDrosophila. We postulated that this correlation might be due to a high rate of intragenic recombination. While these correlations are large enough to be significantly different from zero, their relation to the mean correlations expected under the neutrality models is unknown. This paper reports the findings of a computer analysis determining the correlation for neutral allele pools as specified by the infinite-allele and charge-state models.

In the analysis, mean correlations for a range ofNeμ values and sample sizes of 100 and 1000 genes varied from a high of 0·284 to a low of – 0·780. For the particular values ofNeμ relating to the heterozygosity ofDrosophilaallozymes in natural populations, tests of the empirical correlations to the means expected under the neutral models are made. Most empirical correlations are significantly different from the mean correlations under the neutrality models.
Genetic distance between the Australian Merino and the Poll Dorset Sheep
Authors: Manwell Clyde , Ann Baker C. M.
Published: September 2009

Merinos (189) and Poll Dorsets (106) were compared for genetic variation at 30 loci for blood proteins. ‘Malic enzyme’ and NADH diaphorase I polymorphism occur in Merinos but not in Poll Dorsets, whereas both breeds are polymorphic for haemoglobin, erythrocyte X-protein, serum esterase, catalase and transferrin, although the breeds differ in the presence or absence of certain rare transferrin variants. Poll Dorsets but not Merinos have genetic variation of erythrocyte pyruvate kinase at low gene frequencies; Merinos but not Poll Dorsets have genetic variation of two erythrocyte Gly-Leu peptidases, glucosephosphate isomerase, superoxide dismutase, and NADH diaphorase II, all at low gene frequencies (P< 0·05).

Using Masatoshi Nei's (1972, 1976) standard genetic distance, over all 30 loci, to calculate the time of divergence of the two breeds, we obtainedt= 69700 years – whereas sheep are believed to have been domesticated by man for not more than 11000 years, and ancestors of the British breeds and of the Merino have probably not been separated for more than 2000 years. Several possible explanations for this discrepancy are discussed, including the accuracy of the coefficient of codon change (α), changes in population size and structure, selection, and additional hybridization in the ancestry of the Merino.
Information on the nature oft-haplotypes from the interaction of mutant haplotypes in male fertility and segregation ratio
Authors: Lyon Mary F. , Mason Irene
Published: September 2009

Thet-haplotypet6interacts with brachyury,T, to produce taillessness, and exhibits lethality, male sterility and high male segregation ratio. Mutant haplotypes derived fromt6which have lost the lethality also lose the sterility. We here report that two mutants which have retained the lethality have also retained the sterility and suggest that the two properties of lethality and sterility are due to a factor or region of thet-haplotype located close to the locus oftf. Althought6has a high male segregation ratio, mutants derived from it may have low or normal ratios. In trans heterozygotes of two mutant haplotypes the ratios tended to be equalized, whereas in cis heterozygotes a high ratio liket6was obtained, at least in one case. On this evidence the low-ratio geneLowis reinterpreted as a mutantt-haplotype and designatedtlow. It is suggested that abnormal ratio is due to anA-factor or region located between the loci ofTandtf, so thatt6carries T-, A- and LS-factors which can exist separately and retain their properties.t6may extend less proximally than other naturalt-haplotypes, which in general may involve changes in interstitial heterochromatin.
Evidence from chimaeras for the pattern of proliferation of epidermis in the mouse
Authors: Green Margaret C. , Durham Dianne , Mayer Thomas C. , Hoppe Peter C.
Published: September 2009

The recessive mutant gene downless (dl) causes abnormal texture of the coat and absence of hair on the tail. Thedllocus had previously been shown to act in the epidermis and not in the dermis. To obtain evidence on the pattern of proliferation of epidermis, downless ↔ normal chimaeras were produced by embryo aggregation, and the pattern of normal and mutant hair in the coat was examined. The chimaeras showed a pattern of narrow transverse stripes of normal and abnormal hair. This pattern was similar to that found in mice chimaeric for alleles at the agouti locus known to act in the dermis. This evidence supports the conclusion that the pattern of cell proliferation is similar in dermis and epidermis, and is compatible with the hypothesis that both tissues proliferate by lateral coherent clonal growth from a randomly mixed array of longitudinally arranged cells.
Inheritance of reaction to halothane anaesthesia in pigs
Authors: Smith C. , Bampton P. R.
Published: September 2009

The inheritance of reaction to halothane anaesthesia (so-called malignant hyperthermia syndrome) in pigs was studied in a series of 61 litters by 18 sires from an F3–F4 Pietrain–Hampshire crossbred population. A single locus two allele model allowing for reactors from all three genotypes, was fitted by maximum likelihood. It was concluded that the reaction is due to a single autosomal recessive gene with a frequency of 0·46 (0·44–0·48) and penetrance of 0·95 (0·92–0·98) in this stock.
Dislodgement and thymineless elimination of N-group plasmids
Authors: Pinney R. J. , Jacob A. E. , Hedges R. W. , Smith J. T.
Published: September 2009

Thymineless strains ofEscherichia coliC600 were constructred harbouring both an R factor of the N incompatibility group (R46 or R447b) and a compatible plasmid (Plac-of the A-C group or the Iα plasmid R62), which contained a segment of N group DNA. Selection was made for the transferred plasmid and dislodgement phenomena were manifest either as loss of an entire plasmid or as deletions of a region of plasmid DNA. Even after the two R factors had become established as separate replicons, the N group R factor but not the other plasmid exhibited instability.

Thymine starvation of strain C600thy(R447b/R62) increased the elimination rate of the N group plasmid R447b but no elimination of R62 was observed. However, thymine starvation of strain C600thy(R46/Plac-) not only increased the rate of elimination of R46 but also increased the rate of loss of Plac-. There was no detectable increase in nuclease activity in unstarved R46/Plac-strains and it is concluded that dislodgement of R46 from these strains is not due to induction of the nuclease that has been proposed to be responsible for the elimination of N group plasmids during thymine starvation.

Two variants of Plac-were isolated. These did not dislodge R46 from unstarved R46/Plac-strains and were not lost during thymine starvation even though thymineless elimination of R46 occurred at normal frequency.
Resistance to p-fluorophenylalanine in diploid/haploid dikaryons: dominance modifier gene explained as a controller of hybrid multimer formation
Authors: Lewis D. , Vakeria Dina
Published: September 2009

The gene pfpr-10 in Coprinus confers resistance to p-fluorophenylalanine. The resistance of the heterozygote pfpr-10/pfp8-10 is completely recessive, both in diploids and dikaryons. A dominance modifier Mod+ makes pfpr-10 dominant in a dikaryon but not in a cliploid. It also enhances the degree of resistance in r homozygotes. These results are explained on a hypothetical model based upon a hexameric product of the pfpr-10 gene, with resistance to PFP being proportional to the percentage of homo r hexamers. The Mod+ is presumed to act by keeping the r and s products separate so that hybrid multimers are reduced to a minimum. Critical threshold concentrations of PFP for diploid/haploid dikaryons in 40 different combinations of pfpr and Mod+ genes cover a wide range of gene doses and percentage of homo r multimers. The relationship between the critical threshold concentrations and the calculated percentage of homo r multimers supports the model.
Protein variation in the plaice,Pleuronectes platessaL.
Authors: Ward R. D. , Beardmore J. A.
Published: September 2009

Thirty-nine enzyme loci and seven non-enzymic protein loci have been screened for electrophoretically detectable variation in a population ofPleuronectes platessa, a marine flatfish. The mean heterozygosity per individual is 0·102 ± 0·026, or 0·118 ± 0·030 if the non-enzymic proteins are excluded. The distributions of allele frequencies and single locus heterozygosities are given, and the results discussed with reference to current theories concerning the nature of protein variation.
Derivation of mutantt-haplotypes of the mouse by presumed duplication or deletion
Authors: Lyon Mary F. , Bechtol Kathleen B.
Published: September 2009

The genetic properties of some new mutantt-haplotypes derived from the naturally occurring haplotypet6have been investigated. Several mutant haplotypes gave taillessness with brachyury,T, were viable when homozygous, and when in compound witht6, and all these expressedtfand appeared to have arisen by meiotic crossing-over betweenTandtfin the region of crossover-suppression oft6. The haplotypeth17arose by crossing-over in a stock oft6carrying the translocation T(1; 17) 190Ca, in which the translocation break in chromosome 17 is within the crossover-suppressing region; henceth17could not be separated from T190. It was of the complementary crossover type in that it did not interact withT, and was lethal in compound witht6; its male segregation ratio was normal with heterogeneity. A further haplotype,th20, expressedtf, gave taillessness withT, and was lethal when homozygous and in compound witht6. The expression oftfwas attributed to a deletion, which also covered the loci of the nearby lethals knobbly,Kb, andtw5.th20showed weak complementation oftw5. The haplotypeth7had previously been interpreted as carrying a duplication; it was shown that this duplication was semi-lethal when homozygous. it is suggested that lethal mutantt-haplotypes commonly arise by duplication or deletion but such structural changes are not necessarily at the end of the haplotype, and need not arise by unequal meiotic crossing-over.
On the gene conversion model as a mechanism for maintenance of homogeneity in systems with multiple genomes
Authors: Ohta Tomoko
Published: September 2009

The gene conversion model reported by Birky & Skavaril (1976) has been analytically studied by using the theory of diffusion models of Kimura (1964) in population genetics. It has been shown that the fate of new mutations in systems with multiple genomes may be satisfactorily treated by the diffusion model.
Optimum selection intensities in artificial selection programmes: an experimental evaluation
Authors: Frankham R.
Published: September 2009

An experimental evaluation of Robertson's (1970) theory concerning optimum intensities of selection for selection of varying durations has been carried out using published results from a long term selection study inDrosophila. Agreement of predicted rankings of treatments with expectations was excellent for low values oft/T(generations/total number scored) but poor for larger values oft/T. This was due to the 20% selection intensity treatments responding worse than expected and the 40% treatments relatively better than expected. Several possible reasons for the discrepancies exist but the most likely explanation is considered to be the greater reduction in effective population size due to selection in treatments with more intense selection.
Genetic analysis of larval feeding behaviour inDrosophila melanogaster: II. Growth relations and competition between selected lines
Authors: Burnet Barrie , Sewell David , Bos Marten
Published: September 2009

Growth relations of lines selected for fast or slow larval feeding rate have been compared with those in the genetically heterogeneous control base population from which they were derived. Larvae of the slow strain have reduced growth rate and reach their critical weight for pupation later than unselected larvae. Larvae of the fast strain attain their critical weight at the same time as the unselected control larvae, suggesting that growth rate in the precritical period of development is already maximized in the base population and cannot be improved by increasing food intake. This constraint does not apply to the fixed period of post-critical growth however, since fast feeding larvae give rise to larger adult flies than the controls.

Larval feeding rate is affected by genes located on all three major chromosomes. The small fourth chromosome has negligible effect. Selection for slow feeding rate has led to an increase in the frequency of recessive genes affecting the character. High scores of larvae selected for fast feeding rate depend upon interactions between non-homologous selected chromosomes which individually have little effect. Larval feeding rate in the control unselected population appears to be buffered, firstly by epistatic interactions against the effects of chromosomes tending to promote ‘supra-optimal’ feeding rate and, secondly, by dominance against chromosomes promoting a lowering of feeding rate.

Under conditions of scramble type competition between the selected lines for limited resources, fast feeding larvae have a higher survival rate, and complete their period of larval development earlier to give larger adult flies than their slow feeding competitors. The contribution of larval feeding rate to competitive ability at different levels is discussed, and it is suggested that the effects of change in this behavioural character may be far reaching.
Response to selection for increased pupa weight inTribolium castaneumas related to population structure
Authors: Katz Alan J. , Enfield Franklin D.
Published: September 2009

The effectiveness of selection for increased pupa weight inTriboliumwas compared for three different selection systems. In all three systems the same number of breeding individuals was used each generation. Population L was a large random mating population with 24 males and 48 females selected each generation. The C4and C8populations were each divided into 6 subpopulations (lines) consisting of 4 males and 8 fem ales. Each of the three populations was replicated. In C4, selection for pupa weight was within lines for three generations, followed by a generation of among-line selection when the best two out of six lines were selected. These lines were then crossed to produce 6 new subpopulations, and the cycle was repeated. The C8population was handled in exactly the same manner except that seven generations of selection within lines were practised before each generation of among-line selection. Selection response for the 42-generation period was significantly greater in the L population than in either subdivided population. No consistent differences among the selection systems were apparent when evaluating short-term response for the first 12 generations of the experiment. The results were interpreted as indicating that the influence of multiple-peak epistasis was not of major importance for this trait in determining ultimate response to selection when starting from a base population of previously unselected lines and utilizing a within- and among-line selection regime.
Warfarin resistance: a balanced polymorphism in the Norway rat
Authors: Greaves J. H. , Redfern R. , Ayres P. B. , Gill J. E.
Published: September 2009

The frequency of monogenic resistance to anticoagulant rodenticides in Rattus norvegicus in an area straddling the England–Wales border was monitored from 1967 until 1975. Rats were trapped on farms and tested in the laboratory by administering a dose of warfarin lethal to susceptibles. The mean incidence of resistance was 44% and did not change significantly, despite the extensive use of anticoagulants by farmers during the 9-year period. In 1975 more refined techniques showed that the frequencies of susceptible (SS) and resistant (RR) homozygotes were significantly below the Hardy–Weinberg expectations and simple estimates of the relative fitness ratios for the RR, RS and SS phenotypes were 0·37, 1·0 and 0·68 respectively. In two relatively isolated valleys, where selection with anticoagulants was minimal, the frequency of resistance decreased significantly from 57% to 39% during 1973–5. The results are consistent with the hypothesis that a balanced polymorphism is being maintained. Selection against susceptible homozygotes by the use of anticoagulant rodenticides, and against the resistant homozygote due to its high susceptibility to a primary deficiency of vitamin K gives the heterozygotes a selective advantage. A number of ecological factors that influence the incidence of the resistance are discussed briefly.
Effect of pre-treatment with 5-bromouracil in an ultraviolet sensitive strain ofNeurospora crassa
Authors: Nemerofsky Arnold
Published: September 2009

5-Bromouracil was shown to enhance the mutation frequency in an ultraviolet sensitive strain ofNeurospora crassa (uvs-2) that was previously irradiated with ultraviolet light. The design of the experiment eliminated light or dark repair as possible hypotheses to account for the observed enhancement. Since a similar effect was noted at therib-1 locus inN. crassa, which is not a UV-sensitive strain, it appears that the error prone repair mechanism inN. crassamay be related to post-replication repair. This enhancement may be attributed to the interference of 5-bromouracil with post-replication repair. It is also postulated that the maximum increase in the mutation frequency occurs when the greatest number of unrepaired pre-mutational UV lesions are repaired in the presence of 5-bromouracil.
Re-establishment of breeding stocks of mutant and inbred strains of mice from embryos stored at –196 °C for prolonged periods
Authors: Whittingham D. G. , Lyon Mary F. , Glenister P. H.
Published: September 2009

Breeding stocks were re-established from embryos of various mutant and inbred strains of mice after prolonged storage in liquid nitrogen at the 8-cell stage even with strains where only a proportion of the progeny were of the desired type, i.e. in the ModPand XO strains. Gonadotrophin treatment failed to produce superovulation consistently in any of the strains tested. Although the initial survival of embryos after thawing and culture to the morula and blastocyst stage was highest for embryos from XO mothers (61%), these embryos suffered the heaviest early postimplantation loss after transfer (61%). The proportion of embryos, originally frozen, developing into foetuses and offspring was variable (13% HT, 14% PT, 20% ModP, 14% XO, 21% CBA and CBA-T6) and lower than previously reported for hybrid 3H1 embryos (20–30%). The sex ratio of the liveborn young was within the normal expected limits except for the Modpstrain, where it differed significantly from the exected 2♂:1♀ ratio. The proportion of young of the desired type from the frozen embryos of Modpand XO females was less than expected (17 and 3% respectively). In all cases a normal breeding stock was reestablished whose performance was within normal limits for each strain. Even without further improvements in embryo collection and the freezing techniqueper se, the storage of embryos in liquid nitrogen is an extremely economic way of preserving mouse genetic stocks.
Enrichment and screening of heat-sensitive mutants ofPhysarum polycephalum
Authors: Sudbery Peter , Haugli Kari , Haugli Finn
Published: September 2009

A new method for the isolation of temperature-sensitive mutants ofPhysarum polycephalumis described. It involves enrichment and prescreening of mutagenized amoebae followed by screening at both the plasmodial and amoebal stage. A total of 74 temperature-sensitive strains were recovered of which 26 were temperature-sensitive only as plasmodia, 35 only as amoebae and 13 in both stages. After a shift to the nonpermissive temperature, DNA and protein synthesis were followed in temperature-sensitive plasmodia to discover if the lesion affected functions of the nuclear cycle.
Meiotic recombination in a duplication strain ofAspergillus nidulans
Authors: Van de Vate C. , Jansen G. J. O.
Published: September 2009

The (I; II) duplication strain ofAspergillus nidulanscontains a terminal segment of chromosome I twice, one copy being in the normal position, and the other one translocated to a tip of chromosome II. We show that in selfed cleistothecia (homozygous for the duplication) crossing-over between the two segments of the duplication followed by the appropriate disjunction and distribution of the meiotic chromosomes, results in segregation of recessive markers in the duplication. Alternative segregation mechanisms like the deletion mechanism responsible for mitotic non-conformity, cannot explain the observations. The average segregation frequency of the markeryA2 is 11%. Using the mathematical model outlined in the Appendix to this paper, we estimated the recombination frequency between the translocation breakpoint and theyAlocus from the segregation frequency. The essential feature of the model is the computation of the probabilities of combinations of different tetrad types in quadrivalents. Application of the model leads to the qualitative conclusion that the meiotic recombination frequency within the duplication is increased over the normal level. Elsewhere in the genome the frequencies are either unchanged or decreased. Also in crosses heterozygous for the duplication, an increase by at least a factor of two is found. As judged from the appearance of certain recombinant classes, the quadrivalent frequency in homozygous and heterozygous crosses is 2/3 (random pairing) or slightly higher. The increased recombination is attributed to the same lesions that are responsible for the occurrence of deletions in duplication strains ofA. nidulans.
The expression of the gene asebia in the laboratory mouse: I. Epidermis and dermis
Authors: Josefowicz Wendy J. , Hardy Margaret H.
Published: September 2009

Mice homozygous for the asebia mutation (ab/ab), which have defective sebaceous glands, display abnormalities in several other aspects of the integument. Histological sections showed that hyperplasia of the cellular layers and the stratum corneum of the epidermis is apparent at birth and increases markedly with age. Enlarged intercellular spaces are also noted in the epidermis. The thicker dermal layer of the asebic mice is characterized by increased vascularity, increased cellularity and the abnormal morphology of a large proportion of the ‘fibroblast’ population. Electron microscopy demonstrated the many abnormalities in the dermal fibroblasts as well as large amounts of cellular debris in the surrounding matrix. Collagen and elastin show alterations at the light microscopic and ultrastructural levels. Many features of the asebic dermis resemble those found with mild inflammation and with the lysosomal storage diseases. Changes in the dermis of asebic foetuses were noted prior to epidermal alterations and may mediate the latter.
Sufficient conditions for polymorphism with cyclical selection in a subdivided population
Authors: Hoekstra Rolf F.
Published: September 2009

The combined effect of multi-niche selection and cyclical selection is studied in a deterministic model. Sufficient conditions for protected polymorphism are derived for diploid populations with and without dominance and for haploid populations. These conditions appear to be broader than in the cases of only multi-niche selection or only cyclical selection.
A gene unlinked to mating-type affecting crossing between strains ofPhysarum polycephalum
Authors: Dee Jennifer
Published: September 2009

Two alleles of a gene (rac) unlinked to the mating-type locus (mt) have been identified in strains ofPhysarum polycephalumfrom different laboratories. Heterothallic strains differing inmtalleles cross more rapidly if they differ also in theirracalleles. The recovery of hybrid plasmodia from crosses between apogamic (mth) and heterothallic strains is more likely to be achieved if strains of differentracgenotype are used.
Evidence for transductional shortening of the plasmid obtained by recombination between the TOL catabolic plasmid and the R91 R plasmid
Authors: White G. P. , Dunn N. W.
Published: September 2009

The previously isolated plasmid pND3, arising from recombination between the TOL catabolic plasmid and the R plasmid R91, was transduced by pf16 inPseudomonas putida. Apparent transductional shortening was evident in 25% of the transduced pND3 plasmids. Transductants were isolated which had segregated the antibiotic resistance marker, transfer ability and some of the catabolic functions of the parent plasmid.
Drosophila alcohol dehydrogenase frequencies and temperature
Authors: Gionfriddo Maria A. , Vigue Charles L.
Published: September 2009

D. melanogaster imagoes were collected weekly throughout the summer and early fall of 1976. Their Adh genotypes were determined by electrophoresis. The frequency of the Adh4 isoallele fluctuated throughout the period of study. Correlation coefficients assuming no delay, one week delay, two weeks' delay, three weeks' delay, and a four-week delay of the effect of temperature on the frequency of the Adh4 isoallele were insignificant. It was concluded that temperature alone may not be a selective factor but may be selective in combination with other environmental factors.
The expression of the gene asebia in the laboratory mouse: 2. Hair follicles
Authors: Josefowicz Wendy J. , Hardy Margaret H.
Published: September 2009

Mice homozygous for the asebia mutation (ab/ab) are char1acterized by defective sebaceous glands, a short sparse hair coat from 7 days and progressive alopecia. In addition, we have found that the initial hair follicle rudiments in the skin of these mice are able to differentiate into relatively normal anagen follicles which are often excessive in length and have minor abnormalities of the inner and outer root sheath components. The inner root sheath fails to form the typical transverse corrugations at the level of the sebaceous glands and its cells apparently remain, partially undegraded, plugging the hair canal and adhering to emerging hair shafts. Defects noted in the outer root sheath may be responsible for the failure of inner root sheath degradation. With increasing age, irregularities in hair cycle duration, loss of the originally parallel arrangement of hair follicles and further abnormalities of the individual follicular components are increasingly evident. Follicles in asebic mice have a tendency to form buds and branches which occasionally begin typical follicular differentiation. The consistent failure of the asebic follicles to pass normally through the catagen stage to the telogen stage results in long twisted follicles with abnormal and often loosely anchored hair clubs. The dermal papillae are often abnormal or absent from telogen follicles, while typical germ cells are not formed. Thus the lack of multiple hair follicles, the disorganization of follicles and the progressive alopecia observed in the asebic mice are accounted for. It is suggested that the altered dermal environment and outer root sheath abnormalities may be responsible for many of the follicular defects.
The expression of the gene asebia in the laboratory mouse: 3. Sebaceous glands
Authors: Josefowicz Wendy J. , Hardy Margaret H.
Published: September 2009

Contrary to what their name asebia implies, mice homozygous for the ab gene do possess actively secreting sebaceous glands which develop normally from the follicular outer root sheath, at 18 days post-conception. However, by the 20th day post-conception, these mice exhibit the abnormal sebaceous cytodifferentiation which remains typical of the asebic glands throughout life. Nests of outer root sheath cells below the sebaceous glands also undergo atypical sebaceous differentiation. The smooth membrane system and mitochondria, which appear to be responsible for the orderly accumulation of lipid droplets and sebum production in normal mice, become increasingly abnormal in asebic mice. Fewer lipid droplets form, the smooth endoplasmic reticulum becomes distorted and dilated, and the normal transformation of mitochondria does not occur. Atypical differentiation occurs randomly and ‘differentiated’ cells often degenerate within the asebic sebaceous glands. Of the larger specialized sebaceous-type glands studied, only the Meibomian glands are similarly affected by the asebia mutation, while the anal and preputial glands appear to undergo a more normal cytological differentiation. The abnormalities seen in the asebic sebaceous glands seem to be due to defective regulation of the synthetic or degenerative processes necessary for completion of normal sebum production. Both the defects of sebaceous glands and the unusual characteristics of the epidermis and hair follicles in asebic mice may be initiated by the abnormal underlying dermis or the apparently abnormal endocrine system.
Genetic variation between mice in their metabolism of coumarin and its derivatives
Authors: Lush I. E. , Andrews Kathryn M.
Published: September 2009

Adult females from 19 strains of mice were injected with either coumarin or 7-ethoxycoumarin and the urinary excretion of the umbelliferone produced by the metabolism of these substances was measured. With the exception of C57L the strains fell into three classes as follows: high metabolizers (DBA/1 and DBA/2), medium metabolizers (CBA, 129/Rr, NZB and NZW) and low metabolizers (the other 12 strains). The difference in metabolizing ability between the medium group and the low group of strains was also evident when the 4-methyl derivatives of the same two substances were used. However with the 4-methyl derivatives there was no difference in metabolizing ability between the medium group and the high group. The results are interpreted as evidence that the gene Coh on chromosome 7 comprises two closely linked genes which determine cytochrome P-450 isozymes with different substrate specificities.
The effect of finite population size on models of linked overdominant loci
Authors: Avery P. J.
Published: September 2009

Models of two linked overdominant loci in moderately large, but finite, populations are examined by looking at the variance-covariance matrix of the two gene frequencies and the linkage disequilibrium around stable deterministic equilibrium points. In particular, the effect of genetic drift is examined in cases where, in infinite populations, two stable equilibria with non-zero linkage disequilibrium,D, are maintained. Theoretical formulae are produced and checked by computer simulation. In general, the results show that unless the population size is very large indeed, genetic drift causes the values ofDto vary considerably about the equilibrium values and that for many models, where stable equilibria exist at non-zeroDvalues, a wide range of values ofDhave a high probability. Thus it is very difficult to draw conclusions about the selection regime by measuring Linkage disequilibrium in a finite population.
Genetic variation in plasma thyroxine levels and minimal metabolic rates of the mouse, Mus musculus
Authors: Stewart A. D. , Batty Jennifer , Harkiss G. D.
Published: September 2009

A study of inbred strains of the mouse using competitive protein-binding techniques revealed significant strain variation in the total plasma thyroxine levels and in the plasma-free thyroxine index. Measurements of minimal metabolic rates also showed strain variation, but the positive correlation which might be expected between the plasma-free thyroxine index and the minimal metabolic rate did not obtain. Possible explanations are discussed.
Distribution of linkage disequilibrium with selection and finite population size
Authors: Avery P. J. , Hill W. G.
Published: September 2009

The effects of finite population size, occurring either as a bottleneck in a single generation followed by a large expansion or in all generations, are considered for models of two linked heterotic loci. Linkage is assumed to be tight because it is required if there is to be stable linkage disequilibrium,Dǂ 0, in infinitely large populations. (Dis the difference between gamete frequencies and the product of the gene frequencies.)

If a substantial perturbation of frequencies occurs as a result of a bottleneck but the population is subsequently very large,Dmay take hundreds of generations to return to its stable point. In finite populations, the distribution ofDcan be ⋃-shaped, unimodal or bimodal. The correlation ofDin successive generations is higher with tight linkage and is little affected by selection or the size of the population.

The utility of infinite population studies of linkage disequilibrium and its stable points is questioned, and considerable pessimism is expressed about the possibilities of distinguishing selection and sampling effects at linked loci.
Glutamyl-γ-methyl ester acts as a methionine analogue inEscherichia coli: analogue resistant mutants map at themetJandmetKloci
Authors: Kraus Jan , Soll Dieter , Brooks Low K.
Published: September 2009

Escherichia coliK-12 mutants resistant to glutamyl-γ-methyl ester were isolated. A mutation leading to resistance of up to 1·4 mg/ml of the methionine analogue maps at min 63 and is 13% cotransducible withserAindicating an alteration in themetKgene. Another mutation leading to resistance to 3 mg/ml of the analogue and cross-resistance to other amino acid analogues maps at min 87. This mutation, which has the phenotype of MetJ−, is shown to be situated between theglpKandmetBgenes and thus indicates a different gene order from the published one.
Rate of segregation due to plasmid incompatibility
Authors: Cullum John , Broda Paul
Published: September 2009

We calculated the rates of segregation due to plasmid incompatibility under several simple models. A common feature of all the models that we considered is that incompatibility is caused by the inability of the segregation mechanism to distinguish between two incompatible plasmids.

We measured the rate of segregation due to incompatibility of a pair of ColE1 derivatives under two conditions: (1) One plasmid was introduced into cells carrying the other by conjugation. (2) Cells carrying both plasmids were maintained by selection and then selection was released.

Interpretation of the results was made more difficult by effects of the Plasmids on the host cell's growth rate. These experiments gave results in agreement with the predictions of a random pool replication model. Published results were also in reasonable agreement with this model.
Estimation of meiosis and sporulation efficiencies in the fission yeast by ascus analysis
Authors: Calleja G. B. , Zuker M. , Johnson Byron F.
Published: September 2009

Populations of linear asci are classified according to the number of spores in an ascus. The resultant five numerical classes are further classified into ten spatial classes according to the arrangement of the spores in an ascus and, by inference, into ten historical classes according to the number and origins of failures during the developmental process. An analysis of the observed frequencies of numerical classes allows derivation of the efficiencies of the first meiotic division, the second meiotic division and sporulation in a fission yeast. The analytical method may be useful in locating the site of action of sporulation inhibitors and in identifying meiosis mutants from sporulation mutants.
Variation among inbred strains of mice in adenosine 3′:5′ cyclic monophosphate levels of spermatozoa
Authors: Erickson Robert P. , Butley Martin S. , Martin Susan R. , Betlach Charles J.
Published: September 2009

Spermatozoa from inbred strains of mice were found to vary significantly for levels of cyclic AMP when extractions were performed in a reproducible manner. The F1hybrid between high and low spermatozoal cAMP strains showed spermatozoal cAMP levels typical of the low strain. An analysis of spermatozoal cAMP in individual mice from the back-cross of the F1to the high strain suggested that alleles at more than one locus determine strain differences in spermatozoal cAMP. The major histocompatibility locus of mice,H-2, which had been found to have an effect on liver cAMP levels did not seem to affect spermatozoal cAMP levels.t-Alleles, which appear to alter fertilization rates by effects on motility, had no apparent affects on spermatozoal cAMP.
Additive effects of the genestabbyandcrinkledon tooth size in the mouse
Authors: Sofaer J. A.
Published: September 2009

The semi-dominantX-linked gene tabby (Ta) in the mouse and its recessive autosomal mimic crinkled (cr) produce the same mutant syndrome involving abnormalities of the hair, teeth and certain exocrine glands. Previous work has provided some indication of interaction between these loci in terms of vibrissa number. The results of the present study demonstrate that, for tooth size, mice doubly heterozygous for tabby and crinkled show a more extreme phenotype than either heterozygotes for tabby or crinkled alone.
Intramolecular amplification of the tetracycline resistance determinant of transposon Tn1771 inEscherichia coli
Authors: Schöffl F. , Pühler A.
Published: September 2009

Strains ofEscherichia coliharbouring a conjugative plasmid that carries a transposon for tetracycline resistance (Tn1771) were found to be adaptable to very high tetracycline concentrations. The molecular analysis of plasmids isolated from strains with enhanced levels of tetracycline resistance revealed an intramolecular amplification of the resistance determinant of the tetracycline transposon.

A model for the molecular structure of the transposon is presented, which suggests that there are three repetitive DNA segments on Tn1771. This accounts for the properties both of transposition and of gene amplification.
Allelism of methionine-sensitive mutants ofSchizosaccharomyces pombeto loci involved in adenine biosynthesis
Authors: Strauss Andre
Published: September 2009

Methionine-sensitive mutants ofSchizosaccharomyces pombewere found to map at 16 loci,min1–min16, seven of which are allelic to knownadeloci involved in adenine biosynthesis. The mutantmin1–106was shown to be located within theade6locus by intragenic recombination analysis. Methionine sensitivity of these mutants is reversible by adenine supplementation and their pigmentation is similar to that of the correspondingademutants. We conclude, therefore, that theseminmutants are incompletely blocked in adenine biosynthesis. These observations further indicate that adenine biosynthesis inS. pombeis inhibited by methionine or a metabolite derived from it. For some otherminmutants showing reversibility of methionine sensitivity by leucine or proline, no allelism to knownleuorproloci was detected.
Characterization of fractional mutations inDrosophila: differential inhibition of complete and fractional mutations by inhibitors of repair synthesis
Authors: Mukherjee A. S. , Mandal S. K.
Published: September 2009

The ‘maxy’ technique was used for scoring the frequencies of whole body and fractional mutations in the progeny of males ofDrosophila melanogasterthat had been irradiated with 2000 R, irradiation being followed or preceded by treatment with caffeine or acriflavine. Three 2-day broods were used, and males irradiated without subsidiary chemical treatment were used as controls. Both chemicals whether given as post- or pre-treatment strongly reduced the frequencies of fractional mutants in all broods. The frequency of whole-body mutants was unaffected in the first two broods and suffered a moderate reduction in the third. These results are discussed in relation to the hypothesis that repair processes regulate the development of a primary lesion into either a whole-body or a fractional mutant and that the functioning of the repair enzymes depends on the state of maturity of the male germ cell.
Genetic structure of a natural population of Coriolus versicolor (L. ex Fr.) Quél.
Authors: Todd N. K. , Rayner A. D. M.
Published: September 2009

Experiments were carried out to investigate genetic relationships within a population of Coriolus versicolor (a polyporaceous basidiomyceto causing white rot of wood) present in a birch stump. The population consisted of individual dikaryons occupying longitudinally continuous columns of decay separated from one another by narrow, dark, relatively undecayed interaction zones. These dikaryons were shown to be genetically homogeneous throughout their respective decay columns by dedikaryotization procedures. They were mutually antagonistic when paired in culture, but monokaryons derived from their fruit-bodies were interfertile. Experiments using synthesized dikaryons indicated that antagonism is inevitable between genetically distinct mycelia, but that the intensity of interaction diminishes with increased relatedness. Results of pairings between synthesized dikaryons and monokaryons varied according to the relatedness of the isolates. Antagonism invariably occurred when the monokaryon contained a nucleus differing from both nuclei in the dikaryon, but this did not necessarily prevent dikaryotization. Often in this situation dikaryotized sectors developed in the monokaryon visibly separated by zones of antagonism (‘tracks’). Where the monokaryon contained the same nucleus as one of the components of the dikaryon, antagonism usually occurred initially, but normally the colonies eventually fused.
Mechanism of infertility in t-complex mice
Authors: Archer J. R. , Self S. J. , Winchester B. G.
Published: September 2009

Sperm from mice heterozygous (t/+) for many t-lethal haplotypes show segregation distortion. More offspring inherit the t-haplotype than the normal wild haplotype. In contrast males heterozygous (tx/tv) for two t-lethal haplotypes are sterile although they produce normal-looking sperm. The experiments were undertaken to show whether sperm from tx/tv mice are the same as t-fertile sperm from t/+. Female albino mice were persuaded to mate first with coloured sterile tx/tv heterozygotes and then with normal white +/+ males. With the exception of one litter (from a t-heterozygous male which proved to have been misidentified) all the progeny were derived from the mating with the normal father. We conclude that t-bearing sperm from t-lethal (tx/tv) heterozygotes are inviable, and different from t-sperm in t/+ heterozygotes.
Herbicide-tolerant tobacco mutants selected in situ and recovered via regeneration from cell culture
Authors: Radin David N. , Carlson Peter S.
Published: September 2009

The herbicides Bentazone and Phenmedipharm kill the leaves of intact tobacco plants but do not affect callus cultures. Tolerant mutants were isolated by treating leaves of previously γ-irradiated haploid plants with herbicide then excising and culturing the green herbicide-resistant cell clones on the otherwise yellowed leaves. Among plants subsequently regenerated were a total of ten stable independently isolated mutants. Sexual crosses show these ten represent four Bentazone and two Phenmedipharm loci; all mutants were recessive to wild type.
Genetic analysis of the mutationFemale-lethalinDrosophila melanogaster
Authors: Marshall Terri , Whittle J. R. S.
Published: September 2009

A genetic analysis was made of theFemale-lethal(Fl) locus ofDrosophila melanogaster. This is anX-linked mutation which causes lethality only in females. Other alleles do not complementFland are either lethal or sterile when homozygous in females. Complementation studies onFlalleles demonstrate that there is no simple ranking of these alleles in terms of severity of phenotypic effect. Dosage manipulation ofFlalleles indicates that the sex-specificity is not a consequence of gene dosage effects. Viability studies on males carryingFlalleles show thatFlalleles have no effect on viability regardless of the presence or absence of aYchromosome. TheFllocus is therefore sex-specific. The hypothesis thatFl+ is involved in the establishment of imaginal phenotypic sex cannot be substantiated on the basis of experiments utilizing sex-change mutations.