bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in recombination and genetic disturbance on transferring theH2Lc2linkage group fromGossypium tomentosumtoG. barbadenseandG. hirsutum
Authors: Saunders J. H. 
Published: September 2009

TheH2Lc2linkage region fromG. tomentosumwas transferred through seven successive backcrosses toG. barbadenseandG. hirsutumracepunctatumin which these species were used as bulk female recurrent parents. In the last backcross, BC 7, reciprocal crosses were also made. Recombination values diminished with progressive backcrossing. Other workers have shown that values of the order of 20·0% within the pure species were to be expected. In BC 7 joint estimates forpunctatumwere 0·9% and 0·0% as female and male respectively; the corresponding estimates forbarbadensewere 5·0% and 20·1%.Selective elimination of the donor geneH2on transference topunctatumwas observed in all backcrosses, causing disturbance to the expected 1:1 backcross ratio. Disturbance of a different order was recorded for the segmentH2Lc2transferred tobarbadense. When the heterozygoteH2Lc2/h2Lc2was male andbarbadense(h2lc2/h2lc2) female 50% of theH2Lc2gametes were lost and a 1:2 backcross ratio was observed instead of the expected 1:1. The 1:1 ratio was restored when the heterozygote was the female parent. The lethal interaction of theH2Lc2tomentosumsegment with an inhibitorIBfrombarbadensewas postulated.Differences in the reaction of the genotypes ofG. barbadenseandG. hirsutumracepunctatumto the introgression ofH2Lc2fromG. tomentosumwere discussed in terms of evolutionary divergence of the species.
Natural selection and gene substitution
Authors: Kimura Motoo , Crow James F. 
Published: September 2009

Using models which describe the change, by natural selection, of the actual numbers of genes rather than their relative frequencies, it is demonstrated that the equation familiar to geneticists, i.e.dp/dt=sp(1 −p), is appropriate under a wide range of circumstances. It was pointed out that, for realistic treatment of the evolutionary process through which gene substitutions are repeated, the models must have the property such that the total population number remains constant or nearly constant throughout the process, and is not appreciably influenced by the genes being substituted.The load or cost for a gene substitution was studied assuming a haploid population and the effects on the load of such factors as epistatic gene interaction in fitness, finite population number and slow change of environment were investigated. The load may become very large under a strong ‘reinforcing’ type epistasis between advantageous genes. In a finite population, the load for one gene substitution may be inflated by about unity if the product of the effective population number (Ne) and the selection coefficient (s) is large butNesp0is much smaller than unity, wherep0is the initial gene frequency. On the other hand, slow change of environment may decrease the load somewhat. It was concluded that despite these and other complicating factors, Haldane's original formula, –logep0, for a haploid population (−2 logep0for the case of a diploid without dominance) is still useful for assessing the approximate amount of selective elimination that accompanies the process of gene substitution in evolution.
Gene-environment interactions of theeye-gonemutant inDrosophila melanogasterand a comparison witheyeless
Authors: Hunt David M. 
Published: September 2009

A comparison of the gene-environment interactions of theeygmutant in two different genetic backgrounds clearly demonstrates that the properties of the genetic background play a major role in the control of the gene-environment interactions of this mutant. Similarly, modifier background is important in the determination of the sensitive stages in eye development to a cholesterol-deficient diet.The phenotypic identity of theeyelessandeye-gonemutants suggests a close underlying metabolic and developmental relationship. Possible inter-relations of these two mutant genes are discussed in the light of their gene-environment interactions in a standardized genotype.
Manifestation of eight lethals inCoelopa frigida(F.)
Authors: Burnet B. 
Published: September 2009

The time of action and morphological pattern of damage of eight recessive autosomal lethals inCoelopa frigida(F.) is described. Seven embryonic lethals are phase-specific in their time of action but lethalglassymay cause death at any time from the beginning of the third instar onwards.A method for estimating the preadult viability of heterozygotes for lethals is described. Heterozygotes for lethalE/L3show some impairment of viability, whereas, under conditions of larval competition heterozygotes for lethalE/L4are superior in viability to their wild type sibs.
A search for histocompatibility differences between irradiated sublines of inbred mice
Authors: Godfrey J. , Searle A. G. 
Published: September 2009

(1) A tail-skin grafting method was used to test for histocompatibility differences between members of thirteen sublines of C3H inbred mice, kept in a 1 r./night gamma radiation field for twelve generations, on the average, and separated from each other by about thirty-four generations.(2) No homograft rejections occurred, so there was no evidence to suggest that mutations at histocompatibility loci had taken place in any of these sublines. Calculations show that this finding does not conflict with the idea that a fairly large number of loci are involved, having mutation rates similar to those already known in the mouse.
The ecological genetics of growth in Drosophila 6. The genetic correlation between the duration of the larval period and body size in relation to larval diet.
Authors: Robertson Forbes W. 
Published: September 2009

1. The low but regular positive correlation between body-size and the duration of the larval period in populations ofD. melanogasterhas been studied by selecting for large size or shorter development time on aseptic defined diets deficient in RNA and comparing the results with parallel selection on unrestricted yeast diets or on media in which RNA is not a limiting factor.2. There is a striking contrast according to the nature of the diet during selection. On unrestricted diets and where RNA is adequate there is little or no evidence of correlation between the two characters, but on low RNA media there is a striking correlation whether selection is for large body size or shorter development time.3. This contrast is accounted for in terms of particular changes in larval growth which can be divided into a first stage of growth to a critical size in the early 3rd instar and a second stage thereafter. The duration of the first stage can be greatly prolonged by inadequate diet but the duration of the later stage appears to be virtually unaffected by such variation although the amount of growth and hence final body-size, may be drastically reduced. The different diets which lead to presence or absence of correlation have enabled selection either to extend the growing period, so that the critical stage is reached later at a larger larval size, or to accelerate the growth rate in the later stage.4. Variation in the final stage of growth predominates on unrestricted diets and is responsible for the greater part of the variation in body size in unselected populations. Stabilization of body-size about an intermediate optimum refers especially to growth in this later stage.5. Lines selected for fast development on low RNA media are especially sensitive to minor nutritional variation. Probably only under rather special conditions is it possible to shorten the duration of the larval period and this is compatible with the importance of development time in fitness generally.6. There is evidence that the restriction of early growth, in the 2nd instar, reduces the size of the 3rd instar mouth-parts. Such reduction is correlated with changes in adult size probably because smaller mouth-parts restrict food intake.7. The pattern of larval growth suggests a flexible system which can be adjusted to different ecological conditions since the same body-size can be attained by adjusting the amount of growth effected before or after the critical stage. Differ ences in this respect will involve characteristic differences in reaction to environ mental variation and particular nutritional conditions are likely to influence the way in which adaptive changes are realized.
New results on the genetics of mating types inParamecium bursaria
Authors: Siegel R. W. 
Published: September 2009

1. The four mating-types I, II, III, IV known forP. bursaria, syngen 1 are determined by specific combinations of dominant and recessive alleles at two unlinked loci. Mating-type I is formed by cells with the genotypesAABB, AABb, AaBBandAaBb; type II is controlled by the genotypesaaBBandaaBb; the double recessive,aabbis type III, genotypesAAbbandAabbbring about type IV.2. Clones which are exceptions to these rules for mating-type determination occur in low frequency (2–3%) in one line of descent. All can be explained by assuming either a mutation of dominant geneBto its recessive allelebor to a loss of theBlocus. The data suggest that in four clones, themacronuclear but not themicronuclear genotype is affected; in two clones both nuclei are aberrant.3. The cytogenetic events of conjugation were verified by the use of the new genetic markers. No evidence for uniparental nuclear reorganization, autogamy, was found.
Kinetics ofF-curing by acridine orange in relation to the number ofF-particles inEscherichia coli
Authors: Stouthamer A. H. , de Haan P. G. , Bulten E. J. 
Published: September 2009

Acridine orange does not interfere with the distribution of theF-particles among the daughter cells but inhibits the multiplication of the episome.In growing cells the generation time of the episome in the presence of acridine orange is longer than the generation time of the cell.This lowers the number of episomes per cell to less than two copies at cell division.F-particles rapidly multiply after transfer until a relatively small fixed number (3–4) is reached.
The expression of ‘Hairless’ inDrosophilaand the role of two closely linked modifiers of opposite effect
Authors: Nash David 
Published: September 2009

1.Hairless(H), a dominant mutant ofDrosophila melanogaster, affects the chaetae.2. Various ‘intensities’ of effect are interpreted as representing different times in chaetal development at which deficiency of ‘+Hsubstance’ is encountered. ‘Temperature effective period’ studies confirm this view.3. The chaetae at different sites are liable to characteristically different ‘intensities’ of effect. In other words a particular site tends to be affected at a limited time in its development. If it is supposed that a single period of deficiency of +Hsubstance accounts for effects on all chaetae, then it follows that development of the various chaetae is asynchronous. Some histological observations tend to support this prediction.The implications of asynchrony with respect to pattern formation are discussed.4. It is argued that the source of +Hsubstance may be an endocrine organ, the ring-gland.5. Two modifiersSu-HandE-H, whose expression and linkage relations are described in detail for the first time, are, it is suggested, respectively ‘constitutive’ and ‘super-repressed’ mutations of a ‘regulator’ locus controlling negative feed-back on the +Hlocus.
Genetic recombination inNeurospora crassaandN. sitophila
Authors: Scott-Emuakpor M. B. 
Published: September 2009

Mutant genes in linkage groups I (mating-type chromosome), VI and VII have been transferred fromNeurospora crassatoN. sitophilaby hybridization and repeated backcrossing. Recombination between these genes has been studied from five-point crosses involving linkage group I and three-point crosses involving linkage groups VI and VII of the two species.The results show significant differences in the amount of recombination between some of the genes in the proximal regions of the mating-type chromosomes of the two species. They indicate proximal localization of crossovers in the mating-type chromosome ofN. sitophila. The results also show significant differences in recombination frequency between the genes in linkage group VI and a close similarity in linkage group VII. They further show that the centromere in the two species may not be interfering with crossing-over in its vicinity to such an extent as to be of any evolutionary significance.
Genetic discrimination by means of DNA/DNA binding
Authors: McLaren Anne , Walker P. M. B. 
Published: September 2009

Under suitable experimental conditions, short denatured DNA fragments may be bound by high molecular weight denatured DNA immobilized in agar (‘long DNA’). The proportion of fragments bound depends in part upon the degree of taxonomic relationship between the organisms from which the two DNA components are taken. Before the method can be used as a measure of genetic relationship between closely related species or between intra-specific groups, its resolving power requires to be increased. The present study explores some modifications of the method from this point of view, using the degree of binding between DNA from laboratory mice and rats as a model.Long rat DNA was less effective than long mouse DNA in binding short DNA fragments from either source. It was therefore necessary to test reciprocally, using both short mouse and short rat DNA on long DNA from each species. Combining reciprocals gives a measure of the proportion of fragments bound in within-species and in between-species combinations. With rats and mice, between-species binding was at about 70% of the within-species level. The discrepancy could be increased, and hence the discriminating power of the method improved, if the binding reaction was partially or totally ‘blocked’ with an excess of unlabelled DNA fragments in an appropriate species combination.Even when short and long DNA came from the same source, only about a third of the fragments were bound. The bound and unbound fractions were recovered, and each reincubated with a fresh sample of long DNA. The two fractions then behaved very differently, suggesting that the original DNA preparation is heterogeneous. The initially unbound DNA showed a very low binding ability in subsequent incubations and may be considered virtually ‘unbindable’.When the first incubation is a between-species one, the unbound fraction should include not only this ‘unbindable’ DNA, but also any DNA characteristic of that species alone, and not held in common by both species. If it could be isolated, this DNA fraction might be expected to discriminate maximally between the two species. By using three successive cycles of incubation, a fraction was obtained which showed considerably improved discriminating power, in that it showed only about 30% as much binding in between-species as in within-species combinations.
Maintenance of kappa particles in cells recently deprived of gene K (stock 51, syngen 4) of Paramecium aurelia
Authors: Yeung K. K. 
Published: September 2009

1. Heterozygous (K/k) killer paramecia containing kappa particles from stock 51, syngen 4 of Paramecium aurelia were passed through autogamy, and the kk offspring tested for killing ability and for presence of stainable kappa particles at various fission stages.2. After eight fissions, a small proportion of the paramecia were non-killers, and a few lacked stainable particles. After the 12th fission nearly all cells lacked kappa.3. Mild starvation of the kk kappa-bearing paramecia resulted in complete loss of kappa and conversion to non-killers, even when applied to animals only one fission after the loss of gene K at autogamy.4. The results obtained here show some discrepancy with data obtained earlier, both with kappa, and with mu particles in stock 540, syngen 1. The reasons for this discrepancy are at present not clear.
Mutagen specificity among reversions of ultraviolet-inducedadenine-1mutants ofSchizosaccharomyces pombe
Authors: Clarke C. H. 
Published: September 2009

Ten U.V.-induced mutants at theadenine-1 locus ofSchizosaccharomyces pombediffer not only in their intragenic location but also in their spontaneous, HNO2- and U.V.-induced frequencies of reversion to adenine-independence. Seven mutants reverted with HNO2and of these only two reverted also with U.V.; the other three did not revert with either HNO2or U.V.Genetic analysis of revertants showed that they could be due to suppressor mutations at a locus or loci far from theadenine-1locus, or to events extremely close to, if not identical with, the original site of mutation. Many distant suppressors were found among spontaneous revertants of someadenine-1andadenine-7allles, but such suppressors appear to be less frequent among the fiveadenine-8mutants tested. There are large differences between different sites at the same locus in the proportion of their spontaneous revertants due to distant suppressor mutations. Nitrous acid-induced revertants ofadenine1-,adenine-7, andadenine-8mutants were almost all of a type containing no detectable suppressor mutation. In the three cases studied, U.V.-induced revertants could be either predominantly of a suppressor or non-suppressor type, depending on the particular mutant examined.Striking examples of mutagen specificity were found in which a particular mutant gave mostly suppressor-type revertants with one mutagen, while with another mutagen revertants were mainly of a type containing no detectable suppressor mutation.
Genetic divergence in M. Vetukhiv's experimental populations ofDrosophila pseudoobscura3. Divergence in Body Size
Authors: Anderson Wyatt W. 
Published: September 2009

1. Six initially identical populations ofDrosophila pseudoobscurahave been maintained in population cages for 7 years. Two populations have been kept at 16°C, two at 25°C, and two at 27°C.2. One and a half years after the start, there was no significant genetic divergence in body size among the populations. When the populations were about 6 years old, a striking genetic divergence in body size was found. The genetic difference between the populations having the smallest and the largest mean sizes is over half the total phenotypic change in size between the two extreme temperatures at which the populations were kept. The populations kept at the lower temperature have genetically larger flies than the populations kept at the higher temperatures.3. Accompanying the changes in body size were changes in the time of develop ment from egg to adult, the faster developers being the larger flies.4. The F1hybrids from crossses between Vetukhiv's populations showed non-additivity of the genes for body size, the F1's in most cases being significantly larger than the midparent. There was no change in variability of body size in the F1or F2hybrids.5. The temperature-directed selection for body size found in Vetukhiv's experimental populations may well be similar in kind to that which has produced temperature-oriented geographic gradients for body size in natural populations of several species ofDrosophila.
Selection for developmental canalisation
Authors: Waddington C. H. , Robertson E. 
Published: September 2009

Starting from a genetically variable stock homo- or hemi-zygous for Bar two selection lines were set up, one selected for decreased sensitivity to the effect of larval temperature on eye size (‘canalization line’), the other for increased sensitivity (‘anti-canalization line’). In each generation a sample of larvae was grown at 25°C. throughout life and another sample at 25°C. for the first 48 hours, followed by 18°C. until emergence. In the canalization lines a selection was made of individuals (five males and five females out of 100) least affected by the temperature treatment and the anti-canalization line for a similar number most affected by the treatment. These ten males and females were allowed to mate at random and from the eggs produced random samples were then treated in the next generation in a similar manner in the two temperatures. Precise counts of facet numbers on the right eyes were made at generations 4 and 9 and it was clear that selection had been effective both in decreasing and increasing temperature sensitivity.The whole canalization line can be regarded as a population which has been subjected to disruptive selection for two different criteria: one (small eyes) being regarded as adaptive to the low-temperature regine or habitat; the other (large eyes) being regarded as adaptive to the high-temperature habitat. A similar type of analysis can be applied to the anti-canalization line in which, however, the selective values of the phenotype are regarded as reversed in value in the two habitats. The experimental procedure employed involved not only random mating between individuals selected according to these two criteria but also random allocation of the offspring of this panmictic population to the two habitats of the next generation. This corresponds to a natural population in which there is disruptive selection exerted by two different habitats but no habitat preferences exhibited by members of the population. Under these circumstances, in our experiments, disruptive selection produced only rather slight increases in phenotypic variance, which were rather larger in the anti-canalization than in the canalization lines. Possible reasons for the difference between this result and those reported by Thoday and Gibson are discussed, and it is suggested that an important reason may be the slowness of the response to selection in the first few generations in our lines.
A super-suppressor on the thirteenth linkage group inSaccharomyces
Authors: Oshima Yasuji , Oshima Ikue 
Published: September 2009

It has been proved that the suppression of seven different auxotrophic mutant alleles is brought about by a single super-suppressor allele designatedS.Super-suppressorSis allele-specific rather than locus-specific and is dominant to its wild-type allele.Suppressible mutant alleles show no linkage relationships either among themselves or with the suppressorS.Super-suppressorShas been shown to be closely linked (about 5 stranes) to one of the centromeres other than those of linkage groups I to XII. This establishes a new thirteenth linkage group.The possible mechanism of action of the super-suppressor is discussed.
Compatibility and stability of diploids inCoprinus lagopus
Authors: Casselton Lorna A. , Lewis D. 
Published: September 2009

Artificially selected diploids ofCoprinus lagopuswhen mated in compatible combinations, either together or with haploids, produce dikaryotic mycelia which are typical of normal haploid-haploid dikaryons. In a diploid-haploid dikaryon, the diploid nucleus is not as stable as when alone in a monokaryon but it can persist through repeated sub-culturing into a fruiting body and eventually through meiosis into the basidiospores. In a diploid–diploid dikaryon either one or the other nucleus becomes haploid so that fruiting bodies with two diploid nuclei are never formed. This fact constitutes a restriction on diploidy in nature and a useful method of reducing diploids to the haploid state.Matings that might be considered to be incompatible at theBmating gene show a significant difference which is related to the number ofBalleles common to the mating colonies. Matings with oneBallele in common, e.g.B3B6+B2B3produce fully compatible and normal dikaryons. Matings with twoBalleles in common, e.g.B3B6+B3B6have, at first while the diploid nuclei still persist, the appearance of an incompatible commonBhaploid heterokaryon. This indicates that theBincompatibility system is based not on a complementary action between differentBalleles but on an oppositional action between the same alleles neutralizing theBgene product which is necessary for dikaryon formation.