bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regular responses to selection 3. Interaction between located polygenes
Authors: Spickett S. G. , Thoday J. M. 
Published: September 2009

1. This paper describes further investigations of the high sternopleural chaeta-number lines of Drosophila melanogaster established by directional selection by Thoday & Boam (Genet. Res. 2, 161). The lines are vg 4 with a mean of 35·6 and vg 6 with a mean of 39·2 chaetae per fly.2. Two locatable polygenes, 3a and 3b, distinguish the line third chromosomes from those of Oregon inbred (mean about 20·5, an ancestor of all the lines). These two genes are both located between the markers h and eyg and do not interact.3. There is one locatable polygene at 41·1 ± 1·7 centiMorgans distinguishing the line second chromosomes from those of Oregon. There is no evidence that this gene is a linked complex, and, if it be a linked complex, it is unlikely to occupy more than 2 map units of the second linkage group. It interacts strongly and positively with the gene 3a.4. These three genes account for 80% of the genetic variance of the vg 4 × Oregon F2.5. Two separate regions at 2·4 ± 0·5 and 50·5 ± 0·9 centiMorgans distinguish the vg 6 × chromosome from that of Oregon. They do not appear to interact. Together they interact strongly and positively with gene 3a.6. These five genes account for 87·5% of the chaeta-number difference between vg 6 and Oregon.7. The locatable polygenes on chromosomes II and III each have qualitatively distinguishable developmental effects.8. It is pointed out that, though the genetics of these lines may be unusually simple, the results indicate that attempts to locate specific genes and study their individual effects should be made more often by students of continuous variation. Since the location of the polygene in chromosome II was done using marker genes 45 map units apart, such studies may be practicable even in species whose linkage groups are much less well marked than those of Drosophila melanogaster.
Chromosomal polymorphism in western Mediterranean populations of Drosophila subobscura
Authors: Prevosti Antonio 
Published: September 2009

1. The frequency of the chromosomal types of several western Mediterranean populations of D. subobscura, distributed in a zone running north–south, is analysed and compared with that from an Edinburgh (Knight, 1961) site at a similar meridian as the Mediterranean populations.2. North–south clines are found in the frequencies of several chromosomal types. Some types are more frequent in the north, decreasing gradually southwards; others show the reverse trend of variation.3. The comparison with a similar array of populations from Central Europe and the Central Mediterranean area, indicates that the chromosomal types more frequent in the northern populations are mostly the same, i.e. the standard orders. But chromosomal types with complex inversion orders are the most frequent in southern populations: in some chromosomes, different orders are predominant in Israel, southern Italy and southern Spain.4. The Pyrenees, acting as an ecological barrier, strongly influence the diversity of the populations north and south of the range. This result and the latitudinal clines support the adaptive significance of the chromosomal polymorphism in D. subobscura.5. The index of free recombination of the population from Malaga (in the south of Spain) is higher than in the populations from the northern Mediterranean area. D. subobscura apparently supports the claims of da Cunha & Dobzhansky (1954) and Carson (1955) that a higher level of chromosomal polymorphism occurs in the central areas of the distribution of a species.
The effect of temperature on recombination frequency inNeurospora crassa
Authors: McNelly-Ingle Caroline A. , Lamb B. C. , Frost L. C. 
Published: September 2009

InNeurospora crassa, a change of 2·5°C. in incubation temperature produced highly significant changes in the second division segregation frequency ofasco(Linkage Group VI). A minimum value was found at 25°C. consistently increasing towards higher and lower temperatures over the range 15° to 30°C.Where recombination frequencies in proximal and distal marked regions in Linkage Groups I and VI showed a change, this followed the same pattern as forascowith proximal intervals usually affected; but in one cross a distal region, instead of the proximal, showed a significant change. This behaviour supports the suggestion that heritable factors influencing recombination frequency in specific regions of each chromosome may show differences in temperature sensitivity.Temperature treatments during protoperithecial development prior to meiosis as well as during meiosis had significant effects on recombination frequencies in several cases. Protoperithecia incubated at one temperature and then transferred to a different temperature after conidiation, gave second division segregation frequencies ofascointermediate in value between those obtained with continuous incubation at either of the two temperatures alone.In the present work withNeurospora, the similarity in the relationship between temperature and recombination frequency with the reported results inDrosophilais discussed and suggests that the common temperature/recombination frequency curve is indicative of a possible direct effect of temperature on the recombination processes. Present knowledge of these processes is insufficient to permit any detailed explanation of the temperature effects found but the observed negative relationship between recombination frequency and temperature over the range 15° to 22·5°C. is discussed in kinetic terms.The second division segregation frequency ofascowas found to be increased at all temperatures tested when the asci were mounted for scoring in strong sucrose solution compared to mounting in water.
Studies on the inhibition and mutation ofAspergillus nidulansby acridines
Authors: Ball C. , Roper J. A. 
Published: September 2009

A number of acridines have been tested for ability to inhibit conidia of strains ofAspergillus nidulans. The effectiveness of any one acridine in growth inhibition and killing involves interaction of genotype and conditions of treatment such as temperature, pH, treatment medium and light intensity. Mutant alleles which confer growth resistance to acriflavine are selective in their actions towards other acridines, may differ in their dominance relationships with different acridines and are even selective with regard to the conditions under which they confer acriflavine resistance. Certain pairs of acridines, used simultaneously, show additive effects, potentiation, or annulment by one of inhibition caused by the other.Some of these findings have been applied in a study of factors affecting acridine-induced mutation inAspergillusconidia. Under conditions which permit metabolism, acriflavine induces a high frequency of unstable morphological variants. One such variant has been shown to be a disomic. Using a system of reversion from auxotrophy to prototrophy, acriflavine-induced mutation has been obtained both with high light intensities and in the absence of light. In the latter case recombination as a feature of the mutation process is excluded.
Breeding Systems in tetraploid Rubus species
Authors: Dowrick G. J. 
Published: September 2009

1. The breeding behaviour of the three tetraploid Rubus species R. caesius, R. calvatus and R. laciniatus (2n = 28) has been investigated.2. Megaspore mother cells of all three species always undergo a normal meiosis and embryo-sac formation is of the Polygonum type. Egg cells have fourteen chromosomes.3. There is no evidence for the production of either aposporic or diplosporic embryo-sacs as has previously been assumed.4. The proportion of sexual and apomictic progeny differs in the three species and, in R. laciniatus, varies according to the chromosome number of the pollinating parent.5. The apomictic progeny are produced by diploidization of the reduced egg cells. These diploidized egg cells can subsequently be fertilized in R. laciniatus.6. The versatility in the breeding behaviour of these species is explained on the basis that only one type of embryo-sac is formed and that the developmental behaviour of the egg cell is conditioned by the chromosome number of the pollinating parent. Apomixis in these species is not a consequence of a breakdown of meiosis.
Further studies on the inheritance of lymph proteins inDrosophila melanogaster
Authors: Duke E. J. 
Published: September 2009

The inheritance of three protein fractions of third instar larval lymph inDrosophila melanogasteras detected by starch gel electrophoresis is described. Each of the three is governed by a single autosomal gene. In two, the dominant allele determines presence, and the recessive absence of the respective fraction. The third protein fraction is governed by a single pair of co-dominant alleles.Comparison of the starch-gel pattern to that obtained on cellulose acetate and on polyacrylamide gel fails to show definite sub-fractionation of those protein bands of which the inheritance has been studied.
The interpretation of complementation data
Authors: Gillie Oliver J. 
Published: September 2009

The evidence for complementation maps being linear is examined by analysis of all known complementation maps in micro-organisms, and by constructing maps from mutants randomly sampled from amongst those at theleu-2locus inNeurosporawith known complementing properties. Eleven loci out of thirty-five examined in six micro-organisms have non-linear complementation maps. Two linear maps,his-3andad-3b(having 25 and 35 complementation groups respectively) have a sufficiently large number of groups for it to be likely that if they do not remain linear on testing further mutants, they will at least have a lower frequency of mutants exceptional to linearity than known non-linear loci. On the basis of maps made from mutants sampled from theleu-2data, it seemed unlikely that non-linearity would be observed with less than 24 complementing mutants or 13 complementing groups in the sample, and therefore many loci with linear maps are likely to be found to have non-linear maps when larger samples of mutants are tested. This conclusion is important in attempting to correlate the structure of complementation maps with recombination maps and with functional data concerning enzyme activities.The relationship between the number of complementing mutants, number of groups and number of units at theleu-2locus is described and a statistical method of determining the total number of groups at a locus is discussed.Known complex complementation maps have been replotted according to consistent rules, and are illustrated in a shorthand form. The form of the complex maps is discussed in relation to current hypotheses concerning the interpretation of complementation maps. In particular an interpretation of the ‘circular’leu-2map is given in terms of the theory of complementation proposed by Crick & Orgel (1964).
Genetic analysis of actidione-resistant mutants in the MyxomycetePhysarum polycephalum, Schw.
Authors: Dee Jennifer 
Published: September 2009

1. Improved methods for the culture and preservation ofPhysarum polycephalumamoebae have been developed.2. Strains of amoebae have been isolated which are stably resistant to 4, 8 or 16 μg./ml. actidione.3. Sensitivity vs. resistance to 4 μg./ml. actidione is probably controlled by a single pair of alleles at a locus unlinked to the mating-type locus.4. Plasmodia homozygous or heterozygous for the allele determining resistance at this locus are no more resistant to actidione than plasmodia homozygous for the allele determining sensitivity.
Selection for leukocyte counts in mice
Authors: Chai C. K. 
Published: September 2009

By directional selection for total leukocyte counts from a hybrid mouse stock we have gradually established two lines of mice, LLC (Low Leukocyte Count) and HLC (High Leukocyte Count), which differ both in total and in differential leukocyte counts. A randombred line (RLC) is also being concurrently maintained. Other variations between these lines of mice are in body weight, in the frequencies of coat color genes, reproductive performance, and resistance to X-irradiation. The LLC line was comparatively low in the latter two physiological parameters, and high in variation of body weight.Responses to selection for high and low leukocyte counts were asymmetrical. In the first two generations, responses were irregular; thereafter they were large in the low line (LLC) for two or three generations and then became small in comparison with those of the high line (HLC). At eleven generations of selection, the mean leukocyte count of HLC is about three times that of LLC Responses of the different cell types were proportional to their individual percentages of the total counts. There were sexual differences in the counts of total and individual cell types. Selection for total leukocyte counts affected the proportions of the individual cell types. Heritability estimates based on selection differential and response and on sib relationships yielded values ranging from 0·15 to 0·39.
Quantitative inheritance of red eye pigment inDrosophila melanogaster
Authors: Chauhan Narendra S. , Robertson Forbes W. 
Published: September 2009

1. The genetic and environmental variation of red eye pigment in individuals of a wild population ofDrosophila melanogasterhas been studied by extracting and measuring the pigment content of individual flies, which were also scored for eye and body size.2. Comparison of such variability in the wild population with the individual variation in crosses between inbred lines suggested that 60% of the phenotypic variance is genetic. About 75% of both genetic and environmental variance is due to intrinsic variation of pigment content while the remainder is correlated with eye size, which shows appreciable variation, independent of general body size, as measured by thorax length.3. Selection for high and low pigment content by both phenotypic and family selection led to 40–50% differences between high and low lines after eight genera tions. The response was asymmetrical and proceeded further and faster with selection for lower pigment content. Crosses between high and low lines showed positive departure from intermediacy, suggesting that more or less recessive effects had contributed to the selection for lower pigment content.4. There was some evidence of lower viability in the selected lines but no evidence of lower fertility or gamete viability in more extreme individuals of either sex.5. Comparison of pigment content, eye and body size at different temperatures and under different levels of crowding suggested that the pigment content per ommatidium is subject to a high degree of genetic determination.6. The average pigment content in strains derived from widely separated localities showed substantial variation, independent of both eye and body size.7. Inbred lines, derived from the same population, were found to differ greatly in pigment content. Crosses and the exchange of homologous pairs of chromosomes between two of these lines suggested that one or more completely recessive genes were fixed in both the second and third chromosome of one line, while the same second chromosome effect was also fixed in another line. The second and third chromosome difference reduced pigment content by respectively 30% and 50% and combined additively, judging by the effects of single and joint substitutions of homologous pairs.8. The possibility of combining genetic and biochemical analysis of pigment content is discussed.
Genetical analysis of proline mutants and their suppressors inAspergillus nidulans
Authors: Weglenski P. 
Published: September 2009

1.Complementation between thirteen proline auxotrophs inA. nidulanswas studied. Two groups of mutants with different complementation pattern were found. These two groups could also be distinguished on the basis of recombination tests.2. The spontaneous reversion rate of proline mutants was established. In all cases studied the reversions were due to suppressor mutations. Dominant, semi-dominant and recessive suppressors were distinguished.3. Complementation between recessive suppressors was studied. Only a few of the suppressors obtained could be located in different complementation groups.4. Three suppressor loci were mapped, two of them,su-2andsu-6in chromosome III linked to thephen-2locus, respectively 22 and 26 map units distant, and the third in chromosome I, linked to thead-9locus (1·9 map units).su-2is a mutant at theSu-4 prolocus already identified by Forbes (1956).5. The action of these suppressors is thought to consist in affecting the pathway of arginine synthesis by one of three mechanisms: (1) accumulation of an inter mediate (ornithine); (2) increased activity of ornithine δ-transaminase; and (3) a third, as yet, unclear process possibly involving feed-back regulation of arginine synthesis or the regulation of arginine breakdown to ornithine.
The limits to artificial selection for body weight in the mouse I. The Limits Attained in Earlier Experiments
Authors: Roberts R. C. 
Published: September 2009

1. The results of some selection experiments for body weight in the mouse, conducted in the past in this laboratory, have been examined from the point of view of the limits ultimately reached.2. The limits that are apparently attained do not necessarily remain stable over prolonged periods of time; two large lines showed marked decreases despite continued selection for high body weight.3. Selection for high body weight reached a limit in the region of 30 g. at 6 weeks of age; small mice reached their limit at around 12 g.4. The time taken to reach the limit may vary from ten to thirty generations, even for this one trait.5. The total response for unidirectional selection was between two and six times the phenotypic standard deviation, or three to twelve times the additive genetic standard deviation.6. Consideration of the half-life of the selection responses excluded the likelihood of the chance fixation of alleles unfavourable to the direction of selection.7. The loci contributing to the response could each have an effect amounting to anything from one-half to one phenotypic standard deviation in the base population.8. This indicated that up to twenty loci had contributed to the response.9. The intensity of selection practised was close to the optimum for obtaining the maximum total response.10. The rule of parsimony would indicate the exhaustion of the additive genetic variance as an adequate explanation of the limits attained.
The limits to artificial selection for body weight in the mouse II. The Genetic Nature of the Limits
Authors: Roberts R. C. 
Published: September 2009

1. The effects of long-continued selection for body weight in two lines of mice, one large and one small, are described.2. The large line showed a sharp increase in weight after remaining at an apparent limit for twenty generations. A rare combinational event is suggested as the most likely explanation.3. Reversed and relaxed selection from the large line at the limit failed to yield any response. This indicates that effectively, the additive genetic variance in this line had been exhausted.4. In contrast, the small line at the limit regressed slightly towards the base population when selection was relaxed. Reversed selection yielded a ready response until a new limit was apparently reached. Loci affecting body weight in this line had therefore not been fixed by selection.5. Natural selection, operating on viability between conception and the time when the selection was made, appears to explain best the lack of fixation in the small line.6. Attention is drawn to the necessity of more experimental work to elucidate the genetic nature of the limits to artificial selection.
The general importance of disruptive selection (A comment on Waddington and Robertson's recent paper)
Authors: Thoday J. M. 
Published: September 2009

In their recent paper, Waddington & Robertson (1966) discuss the general importance of disruptive selection and make various points that call for comment.First, their statement that ‘It is most desirable that Thoday's results … should be repeated, with special attention to the strict virginity of the flies used, …’ appears to some readers as a scarcely veiled imputation that my experiments, especially that of Thoday & Gibson (1962), were executed without technical competence, though Waddington has informed me such imputation was not intended.
Recombination within theYlocus inAscobolus immersus
Authors: Kruszewska A. , Gajewski W. 
Published: September 2009

Mutants of theYlocus differed appreciably in their basic conversion frequencies (frequencies of conversion in one-point crosses) to wild type. The differences in the basic conversion frequencies in the opposite direction, i.e. from corresponding wild-type allele to mutant, were in general not pronounced. For some alleles frequencies of conversion in both directions were similar, but for the others they differed markedly. No evident correlation between the position of mutants on the map and their basic conversion frequencies was observed.In two-point crosses in repulsion, the great majority of recombinant octads were of conversion type. In these crosses symmetry or asymmetry of conversion depended mainly on similarity or differences in basic conversion frequencies of mutants crossed. In crosses between mutants from different clusters the recombination frequencies were near to the sums of their basic conversion frequencies. Such ‘mutant specificity’ makes it impossible to establish the linear order of mutants on the basis of recombination frequencies in two-point crosses.The results of two-point crosses in repulsion between mutants within clusters pointed to the influence of one allele on the frequency of conversion of another one. This ‘marker effect’ was also evident in some three-point crosses.The frequencies of simultaneous conversions in two-point crosses in coupling did not show negative correlation with the distances between the mutants involved.It seems that many of the data presented here are most easily explained by recently developed hybrid DNA models.
A genetic analysis of resistance to nystatin inSaccharomyces cerevisiae
Authors: Ahmed K. A. , Woods R. A. 
Published: September 2009

1. A number of stable nystatin-resistant mutants of the yeastSaccharomyces cerevisiaehave been isolated from platings of a sensitive wild-type strain on low concentrations of the antibiotic.2. These mutants were found to be resistant to 10, 15 or 60 units of drug/ml.3. Analysis of meiotic segregants from crosses of these mutants to wild-type indicate that resistance is determined by two types of genes; resistance genes and modifiers.4. Functional analysis of the mutants demonstrated the existence of three recessive resistance genes,nys-l,nys-2 andnys-3 and thatnys-1 andnys-2 were linked.5. Genetic analysis showed thatnys-1 was affected by two modifiers,Mnys-1 andMnys-2, but that onlyMnys-2 affectednys-2 andnys-3.6. The modifiersMnys-1 andMnys-2 are dominant.7. An investigation of the effects of temperature and medium on resistance demonstrated marked interactions between genotype and environment for both the resistance genes and the modifiers.8. Second-step mutants have been isolated by plating first-step mutants on higher concentrations of the drug. Some of these are resistant to 800 units/ml.9. Some possible mechanisms of nystatin resistance are discussed.