bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetical control of the anaphylactoid reaction in rats
Authors: Harris J. M. , Kalmus H. , West G. B.
Published: September 2009

1. A recessive autosomal gene, dx, preventing the anaphylactoid reaction has been discovered in a stock of Wistar albino rats from the Agricultural Research Council, Compton.

2. Segregation occurred in the F2 generation derived from crossing pure-bred reactor rats and pure-bred non-reactor rats.

3. Non-reactivity was outbred into non-albino stocks and was shown to segregate independently of the albino gene c and not to be closely linked to the colour genes, P and A.

4. The mutation from Dx to dx may have arisen a few years ago in one of the Wistar colonies before it was split into sub-lines.

5. The dx gene is fixed in several brother-sister mated sub-lines and appears to be in equilibrium with Dx in some less inbred closed-populations.
Selection using assortative mating inDrosophila melanogaster
Authors: McBride Glenorchy , Robertson Alan
Published: September 2009

The effectiveness of the assortative mating of selected individuals in increasing selection response was tested, using abdominal chaeta score inDrosophila melanogaster. Three paired comparisons were made. In two sets of lines with 10 matings per line, individual score was used for selection and as the basis for the assortative mating. In the third set with 20 matings per line an index of individual and family score, designed to maximize rate of response, was used.

The intensity of selection was one in ten in all lines. Flies were raised in vials and individual pedigrees were kept.

In all comparisons, assortative mating gave a greater selection response, this being partly due to a greater realized heritability and partly to a greater selection differential. The effect of the assortative mating was largest in the index selected lines. With random mating, the effectiveness of the index selection itself when compared to individual selection was in accordance with theory.

In two comparisons, assortative mating increased the rate of inbreeding. The highest rate of inbreeding was observed with index selection and assortative mating, even though there were here twice as many matings as in the individually selected lines.

In the individual selection lines, the effective population size was 7·4 pairs of parents, compared to the actual value of 10 and in the index lines 7·0 compared to 20. In the former, only one-half of the matings in the initial generations made any permanent contributions to the line and in the index lines only one-third. Within generations and lines, there was a significant positive correlation between the mean score of a family and its inbreeding coefficient.

It is suggested that assortative mating is a method of increasing selection response in some situations. Its particular characteristic is that it becomes more powerful when the heritability is high whereas all of the other environmental aids to individual selection are more effective when the heritability is low.
On the maximum avoidance of inbreeding
Authors: Kimura Motoo , Crow James F.
Published: September 2009

Mating systems in which the least related individuals are mated have been designated by Wright as having maximum avoidance of inbreeding. For such systems the initial rate of decrease in heterozygosity is minimum. However, some other systems have a lower rate of decrease in later generations.

Circular mating, in which each individual is mated with the one to his right and to his left, leads to an asymptotic rate of decrease in heterozygosity of 1– λ ˜ π2/(2N+ 4)2compared with 1/4Nfor maximum avoidance systems. Circular pair mating, in which for example each male progeny is moved one cage to the right, leads to 1– λ ~ π2/(N+ 12)2. Other similar systems are discussed.

For minimum gene frequency drift, a mating system should have a constant number of progeny per parent and the population should be broken up as rapidly as possible into the maximum number of lines. The gene frequency variance at generationTwithin a line is

whereNis the number in the line andHtis the proportion of heterozygotes in generationt. Although the three mating systems, circular, circular pair, and maximum avoidance (and many others) have the same amount of random drift ultimately, at any generation circular mating has the smallest drift variance,VT, and circular pair next smallest.
The interpretation of data from transduction experiments
Authors: Dawson G. W. P.
Published: September 2009

1. Data from transduction experiments withSalmonella typhimuriumcan be interpreted in terms of frequencies of recombination by accepting the arguments of Ozeki that all transduced fragments that include a particular locus are equal in length.

2. From a two-point transduction the ratio of the two classes of transductants is not a measure of the ratio of the frequencies of recombination in the two relevant regions but only provides maximum and minimum values for this ratio.

3. From three-point transductions the frequencies of recombination in the regions between the markers, and between the terminal markers and the ends of the fragment, can be estimated.

4. The difficulties of interpreting data from experiments in which a single factor is transduced are briefly discussed.
Cellular damage associated with multiple mating inE. coli
Authors: Gross J. D.
Published: September 2009

In crosses in which the ratio of Hfr to F- cells was varied it was found that with one group of Hfr strains the yield of recombinants increased linearly with donor concentration until the number of donor and recipient cells were approximately equal. With other Hfr strains marked deviations from linearity were observed at Hfr: F−ratios greater than 1:5 and in crosses with one particular F−strain the yield of recombinants actually decreased progressively as the Hfr concentration was raised beyond this value. The deviations from linearity observed with this group of strains have been shown to be due to damage to F−cells which mate simultaneously with several Hfr cells.
A genetic analysis of CRM negative mutants at the td locus ofNeurospora crassa
Authors: Kaplan S. , Suyama Y. , Bonner D. M.
Published: September 2009

The possibility that primary CRM−isolates at the td locus ofNeurospora crassaare multisite lesions has been examined. By comparing the behavior of primary CRM−mutants to known multisite CRM−mutants in the genetic tests of recombination and reversion, it can be concluded that primary CRM−mutants are not multisite. The genetic implications of a CRM−and CRM+mutant have been discussed.
The effect of inbreeding on temperature acclimatization inDrosophila subobscura
Authors: Bowler K. , Hollingsworth M. J.
Published: September 2009

1. Rates of gain and loss of acclimatization to temperature of males from two inbred lines and the hybrids between them were measured by recording their survival times in dry air at a lethal temperature (34°C).

2. All hybrid males lost acclimatization to temperature more quickly than did inbred males. B/K males gained acclimatization to temperature more quickly than any other group, but the K inbred males gained acclimatization more quickly than did either the K/B males or the B males. In all cases acclimatization is gained more quickly than it is lost.

3. The extent of acclimatization to temperature, as measured by the difference in survival times of 15°C. and 25°C. acclimatized flies in a range of lethal temperatures, was not found to be different in inbreds and hybrids.

4. The results suggest that hybrids can produce the enzymes necessary for acclimatization to temperature more rapidly than inbreds and confirms the hypothesis that hybrids are biochemically more versatile than inbreds.

5. The difference between the rates of gain and loss of acclimatization to temperature suggests that the processes involved in the enzyme changes are temperature dependent.

6. The absence of a difference in the extent of acclimatization to temperature indicates that both inbred and hybridD. subobscuraare capable of producing those enzymes necessary for temperature acclimatization.

7. The high values of the temperature coefficients for heat death indicate that this process involves protein (enzyme) denaturation.

8. An ageing effect was observed in inbred flies.
A developmental-genetic study on panicle characters in rice, Oryza sativa L.
Authors: Sakai Kan-Ichi , Shimamoto Yoshiya
Published: September 2009

By comparing genetic correlations between an X-rayed and a control population of rice, parameters for the strength of pleiotropic effects of quantitative genes have been estimated. It is evident that the gene-set which is responsible for main rachis formation and is therefore of primary importance for panicle formation, is pleiotropically controlling the development of rachillas and basal internode. It is found that the pleiotropic control over the development of higher rachillas is very powerful but less strong over the lower ones and basal internode.

Developmental relationships among these characters have also been investigated by measuring the genetic correlations between their developmental instabilities. The basis of our inference is the hypothesis that if two characters which are found to be pleiotropically controlled by the same set of genes take their own developmental paths from a very early stage, they will show only slight correlation between their developmental instabilities. If, on the contrary, they are taking the same developmental path and their differentiation sets in late, the correlation coefficient will be high.
Induced mitotic crossing-over in relation to genetic replication in synchronously dividing cells ofUstilago maydis
Authors: Holliday Robin
Published: September 2009

A method is now available for synchronizing the division of populations of cells of the smut fungusUstilago maydis. In two experiments carried out with a diploid strain heterozygous for several biochemical markers, samples of cells were removed at intervals through the synchronized division cycle and treated with a constant dose of ultra-violet light. Cell survival and the frequency of the various recombinants resulting from induced mitotic crossing-over were recorded. In addition the period of DNA synthesis in the unirradiated population has been measured. During this period the cells are very sensitive to ultra-violet light and those that survive contain the highest proportion of induced recombinants. In so far as the markers make it possible to locate the position of cross-overs, cells which are irradiated early in the period of genetic replication show most crossing-over towards the ends of the chromosome arms, whilst cells which are treated late in this period show crossing-over near the centromeres. The data are most easily interpreted by supposing that chromosome replication begins at the ends of the arms and proceeds to the centromere, and that the temporary interruption of this process by ultra-violet light can result in pairing and crossing-over in the vicinity of the points of interruption.
The breakdown of the restriction mechanism in zygotes of Escherichia coli
Authors: Glover S. W. , Colson C.
Published: September 2009

In zygotes from matings between Hfr, F′ or F+ donors of E. coli K and F− recipients of E. coli B the restriction of λ. K and λ.C is 100 times less than in unmated B cells. This decrease in the capacity of zygotes to restrict phage λ is transient and is not related to the transfer of genes controlling host-induced modification during the cross.
The production of recessive lethals by calf-thymus DNA in Drosophila
Authors: Mathew C.
Published: September 2009

Calf-thymus DNA was mixed with the larval food of Drosophila melanogaster and complete and mosaic lethals were scored in both the X- and 2nd chromosomes. There was a decided mutagenic effect on the 2nd chromosome in both sexes. No complete sex-linked lethals were produced in males, but the production of a moderate number of complete lethals in females and of mosaic lethals in both sexes suggests that, in the absence of germinal selection, the X-chromosome is not completely refractory to the treatment.

The extension of the 2nd chromosome test to later generations showed that mosaics often gave rise to further mosaic progeny. Tests for allelism showed that lethals in the same mosaic line formed series of overlapping deficiencies, indicating that the primary effect in these cases was a transmitted instability of a narrow chromosomal region. Cases in which several mosaics arose out of one mosaic parent show that this instability must have replicated as instability.
Transferrin and post-albumin polymorphism in East African cattle
Authors: Ashton G. C. , Lampkin G. H.
Published: September 2009

The serum transferrin and post-albumin phenotype distributions of 228 Sahiwal, 138 Nganda, 265 Boran, 114 Tanganyika Shorthorned Zebu, 72 Teso and 267 Ankole cattle from East Africa were determined.

Five transferrin alleles, TfA, TfB, TfD, TfE, and TfF were present in all the breeds examined, and a sixth allele, TfG, was present in three of the Borans. TfE and TfF were the most frequent alleles, except in the Nganda cattle where TfA was the most frequent. TfB had a frequency of less than 0·1 in each breed. Two post-albumin alleles, PaF and Pas, were present in each breed. In each breed except Sahiwal PaF was two to three times more frequent than Pas. In the Sahiwal PaF and Pas had about the same frequency. It was concluded that both transferrin and post-albumin gene frequencies in East African cattle differ significantly from the corresponding frequencies in European cattle.

There was no evidence of an excess of heterozygotes in the post-albumin system other than that expected from the use of relatively small numbers of bulls in these herds. However, allowing for the same factor in the transferrin system, there appeared to be an excess of transferrin heterozygotes in the cattle populations sampled although the extent of this excess could not be calculated accurately.
The two-way selection of mutants and revertants in respect of acetate utilization and resistance to fluoro-acetate in Aspergillus nidulans
Authors: Apirion David
Published: September 2009

An extension of two-way selection (i.e. selection of mutant from wild-type and vice versa within the same locus and with the same efficiency) to four different mutational or segregational situations was made possible by using acetate, fluoro-acetate and other substances related to their metabolism.

Two types of mutants resistant to fluoro-acetate were selected, the first of which (designated fac) cannot grow on acetate as the sole carbon source, while the second (designated fan) can.

Commencing with either a fac or a fan strain a double fac fan strain may be isolated, which is much more resistant to fluoro-acetate than either single mutant strain. Such double mutant strains may also be obtained by crossing a fac to a fan strain. Various characteristics of growth response of these strains on various media were observed.

fac mutants are recessive and map in three meiotically unlinked loci, one in linkage group V and two in linkage group VIII.

fan mutants are recessive and map in five loci, one in each of the linkage groups V, VII and VIII, and two linked in linkage group VI.

Most fac mutants isolated did not revert and this failure is considered genuine. Of the revertants tested, most resulted from extra-cistron suppressors, while revertants of two fac mutants resulted from very closely linked or intra-cistron suppressors.

It is argued that the findings indicate the existence of two pathways for acetate utilization in Aspergillus nidulans, a major and a minor; fac mutants are blocked in the major pathway, fan mutants in the minor pathway.
The effects of mating systems and selection on pupa weight inTribolium
Authors: Wilson S. P. , Kyle W. H. , Bell A. E.
Published: September 2009

An experimental evaluation of the effect of mating systems and selection upon an additive trait thought to be highly heritable was made. There were two similar replications. Each consisted of a mass selected and randomly selected group, with five mating systems within each group.

Realized heritabilities in the mass selected lines were considerably less than was expected prior to the initiation of the experiment, and averaged approximately fourteen percentage points less than heritability estimated from the zero generation. This in turn resulted in smaller correlations between the genotypes of mates than had been previously expected in the assortatively and disassortatively mated lines.

The average response of the mass selected, assortatively mated lines was slightly more than the mass selected, randomly mated lines, though not statistically significant. This result seems to conform to theoretical expectations.

In the mass selected lines, estimates of phenotypic and genetic variance declined regardless of mating systems. There was a tendency for phenotypic variances to decrease in the randomly selected lines, but this was not the case for estimates of genetic variance.

As an aid to selection, it seems that assortative mating would be of little value with traits of low or intermediate heritability but might be useful if the trait is highly heritable.
Genetic analysis of liver catalase activity in two substrains of C57BL mice
Authors: Heston W. E. , Hoffman Harold A. , Rechcigl Miloslav
Published: September 2009

The level of liver catalase activity in substrain C57BL/6 mice is only approximately half that in substrain C57BL/He. That this difference was due to a single major gene with low level of activity dominant to high was indicated by analysis of the F1, F2, and backcross hybrids and confirmed by progeny tests of first back-cross male segregants. The gene symbolCeis suggested.

The absence of any difference between reciprocal hybrids indicated no extra-chromosomal maternal influence.

There was no evidence that this gene controlling liver catalase had any influence on the level of kidney catalase activity for this did not vary between the two parent substrains or the hybrid groups.

Males consistently had higher liver and kidney catalase activity than females. The difference was more pronounced in respect to kidney catalase, males having about twice the activity found in females.
The replication of metagons and mu particles from Paramecium in another cell—Didinium
Authors: Gibson Ian
Published: September 2009

1. The maintenance of mu particles and metagons from Paramecium aurelia (stock 540, syngen 1) in another ciliate protozoan Didinium nasutum has been shown to occur.

2. It has been shown that mu particles could not be supported in Didinium without metagons. One particular strain of Didinium has, however, never been able to support mu even when metagons were present.

3. The continued production of metagons in Didinium was shown to take place even when the Didinium was fed on killer Paramecium of genotype m1m1m2m2.

4. After destruction of the metagons in Didinium by ribonuclease there was no subsequent reappearance of metagon activity.

5. Metagons and mu particles were eliminated from Didinium during encystment.

6. It is considered that the increase of metagons in Didinium is due to self-replication. In Paramecium the metagons replicate only slowly or not at all.

7. It is concluded that the metagon is a gene product in Paramecium which takes on at least one other property, replication, when introduced into Didinium.
Mapping of purine markers inEscherichia coliK 12
Authors: Stouthamer A. H. , de Haan P. G. , Nijkamp H. J. J.
Published: September 2009

A number of mutants ofE. coliK 12, deficient in purine biosynthesis, have been isolated and the biochemical blocks have been determined. The mutations were mapped in conjugation experiments. In some cases the differences in penetration times were too small to determine the exact order of the loci by interrupted mating experiments. In these cases the recombination frequencies were determined in four factor crosses. In this way the location of eleven different purine markers has been determined. The loci are scattered over the chromosome. Only two groups of linked genes were found.
Low recombination frequency for markers very near the origin in conjugation inE. coli
Authors: Low Brooks
Published: September 2009

By performing matings using various Hfr strains having different origins of transfer, it has been observed that male chromosomal markers located very near the origin of transfer in conjugation inE. coliappear in recombinants with a lower frequency than expected from an extrapolation of the transfer gradient. The effect is greatest for markers closest to the origin, and becomes negligible for markers transferred more than 4–5 min. after the origin. The results suggest that in the zygote a random cross-over between male and female genomes is necessary somewhere between the origin and any male marker in order for that marker to appear in a viable recombinant. It was also deduced that the entry time for the origin itself occurs after a 3–5 min. delay after mixing male and female cells together.
Mutagenesis with light and proflavine in phage T4 II. Properties of the mutants
Authors: Ritchie D. A.
Published: September 2009

In summary,rII mutations induced by exposure of T4 phage particles to either visible light or proflavine are acridine revertible. In both cases mutation occurs without inactivation. TherII mutations induced by the photodynamic action of proflavine on T4 phage particles are equally divided between the acridine revertible and base analogue revertible classes. It is proposed that photodynamic action induces base analogue mutations and that the acridine revertible category arises from the separate effects of light and proflavine.
Effect of inhibition of DNA synthesis on mating inEscherichia coliK12
Authors: Hollom Susan , Pritchard R. H.
Published: September 2009

From studies involving inhibition of DNA synthesis in Hfr strains ofEscherichia coliK12, either by thymine starvation (Pritchard, 1963) or amino-acid starvation (Suit, Matney, Doudney & Billen, 1964), during mating withF−strains, it has been concluded that transfer of DNA from males to females can occur in the absence of DNA synthesis. This conclusion is at variance with the hypothesis (Jacob, Brenner & Cuzin, 1963) that the energy required for transfer is derived from the process of DNA replication. On the other hand, a second prediction from this hypothesis, that one polynucleotide chain of the DNA transferred during mating will have been synthesized during transfer, is strongly supported by recent experiments (Ptashne, 1965; Blinkova, Bresler & Lanzov, 1965; Gross & Caro, 1965).
Some observations on asymmetrical correlated responses to selection
Authors: Bohren B. B. , Hill W. G. , Robertson A.
Published: September 2009

The pattern of changes of the genetic covariance between two characters on selection was examined in an effort to explain the asymmetry of correlated responses in two traits, or of the same trait in two environments, frequently observed in experimental results.

The algebraic conclusions were further examined by model selection experiments using a computer. The computer was programmed to calculate the change in gene frequency from generation to generation and to calculate from it the expected changes in genetic variances and covariance as selection proceeded. This procedure was carried out with several models of gene effects and gene frequencies.

Asymmetry of the genetic covariance, and consequently of the correlated responses, resulted when the relative change in gene frequency at the loci contributing positively and negatively to the covariance depended on the trait selected. The conditions necessary for the development of asymmetry were examined and the results suggest that any symmetry found in an experiment is perhaps more surprising than asymmetry. Probably the most frequent contribution to asymmetry in practice will be from loci contributing negatively to the covariance and having frequencies other than 0·5.

Accurate prediction of correlated response over many generations is therefore not possible without prior knowledge of the composition of the genetic covariance, as well as its magnitude. The validity of existing theory for the prediction of correlated responses is likely to be much poorer than for the prediction of direct responses. Predictions would then have to be based on the genetic parameters estimated in each generation.
Curtailed, a new dominant T-allele in the house mouse
Authors: Searle A. G.
Published: September 2009

Curtailed (Tc) is a new T-allele which leads to complete or near-complete absence of the tail in heterozygotes, apart from a small caudal filament. Other heterozygous defects include absence of the axis odontoid process and of the nuclei pulposi, a tendency to have rib and vertebral fusions and a slight decrease in the average number of presacral vertebrae. Tc is lethal when homozygous, causing similar but more extreme defects than T, with absence of all limb-buds and non-closure of the neural folds. A comparison of Tc with other mutants suggests that the anomalies are mainly the result of more severe effects on the notochord-mesoderm system than in T. Differences between the genetic behaviour of T, Tc and Th are discussed.
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.
The relation of resistance transfer factors to the F-factor (sex-factor) ofEscherichia coliK12
Authors: Meynell Elinor , Datta Naomi
Published: September 2009

The genetic elements promoting conjugation associated with transmissible drug resistance are of two or more kinds. Experiments with phage specific for F+bacteria have shown that one large class differs from F essentially only in the production of a cytoplasmic repressor which limits the synthesis of the specific F pilus, whether by the RTF itself or by F when this is present in the same cell.
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.
‘Grizzled’, a mutant in linkage group X of the mouse
Authors: Bloom Joyce L. , Falconer D. S.
Published: September 2009

Grizzled (gr) is a recessive gene with complete penetrance but reduced viability. It is linked with waltzer (v) in linkage group X, the recombination frequency being 14·6 ± 2·6%. Its visible effect is to dilute the yellow pigment of the hairs. Body weight is reduced by about 25% atbirth and remains at about 10–20% below that of non-grizzled litter mates. Viability up to the time of classification is about 50–60% of that of non-grizzled litter mates. The mortality of grizzled homo-zygotes occurs at all stages from about 10 days of gestation up to the time of classification. No specific cause of the mortality was evident.
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.
A direct determination of nuclear distribution in heterokaryons ofAspergillus nidulans
Authors: Clutterbuck A. J. , Roper J. A.
Published: September 2009

A cytological study has been made, inAspergillus nidulans, of haploid and diploid homokaryons and of heterokaryons formed between them. The effective region of growth was shown to extend about 600 μ behind the growing edge of the colony and to correspond largely with the tip cells. Acridine fluorescence gave unselective staining of all nuclei; projected nuclear areas, and their distributions in individual hyphae, were determined for the homokaryons and heterokaryons. Diploid and haploid nuclei differ in mean projected area but the overlap of their size distributions precluded unequivocal classification of individual nuclei in diploid–haploid heterokaryons. However, it was shown that the hyphae of a heterokaryon differ in nuclear ratios. This, and other evidence, strongly support the suggestion that heterokaryon maintenance and adaptation occur through interhyphal rather than intrahyphal selection.
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.
The effect of various physiological conditions on host-controlled restriction inEscherichia coliK(P1)
Authors: Schell J. , Glover S. W.
Published: September 2009

Growth of K(P1) bacteria under conditions which lead to a reduction in the level of nucleases also leads to a reduction of their ability to restrict the growth of λ.C. Experiments designed to estimate the time after adsorption at which restriction takes place indicate that phage DNA is probably restricted by a nuclease while passing through the periplasm.
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.
Differences in bristle-making abilities in scute and wild-typeDrosophila melanogaster
Authors: Young S. S. Y. , Lewontin R. C.
Published: September 2009

Difference in bristle-making abilities in extreme scute and in wild-typeDrosophilawere investigated using flies mosaic for the two kinds of tissues. It was found that both wild-type and scute tissues were autonomous with respect to bristle differentiation. From the experimental evidence it was postulated that the differences in bristle-making abilities between the two genotypes might be due to differences in tissue competence rather than differences in pre-pattern or in level of bristle-making substances.
Induction of invertant males inE. ColiK12
Authors: Espardellier-Joset F. , Fournier R.
Published: September 2009

A number of Hfr strains have been studied as to the action of radiations on the transmission of their genetic material to female cells. They form two classes, one in which irradiation produces only lesions that prevent transfer, and one in which new modes of chromosome transfer seem to be induced. One group of strains, derived from a common F+male, appears to give rise to the same induced mode of transfer, while no correlation could be found in the other Hfr's 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.
Amino acid deprivation and its effect on mating ability inEscherichia coliK12
Authors: Fisher K. W.
Published: September 2009

The conclusion by Suit, Matney, Doudney & Billen (1964) that Hfr donor cells ofEscherichia coliK12, starved of required amino acids can mate, has been re-examined. It appears that their conclusion is not valid and that apparent fertility of amino-acid starved cells is due to cross-feeding by the F−cells. The relationship of this result to the alternative mechanisms for chromosome transfer inE. coliis discussed.
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.
Lack of evidence that inactivation of the mouse X-chromosome is incomplete
Authors: Lyon Mary F.
Published: September 2009

The fact that the X-linked genes scurfy (sf) and sparse-fur (spf) of the mouse do not produce a mosaic effect in heterozygotes had been taken, by other workers, together with results from X-Autosome translocations, as evidence that inactivation of the mouse X was incomplete. In this paper it is argued that absence of a mosaic effect is not adequate evidence that a gene is not inactivated. The argument was backed by an experiment in which thespfgene was introduced heterozygously into females carrying an X-linked translocation resulting in non-random X-inactivation with the same X active in all cells. When the mutant (spf) allele was on the active X its effect was fully expressed, indicating that the normal allele on the structurally normal inactive X was undergoing inactivation. Argument is further presented that results from X-Autosome translocations do not indicate the degree of completeness of inactivation in a structurally normal X. Hence, there is no evidence that inactivation of the mouse X is incomplete, although evidence from XO females does suggest that it may be incomplete in man.
Selection in natural populations V. Indian Rats (Rattus Rattus)
Authors: Valen Leigh Van , Weiss Robin
Published: September 2009

In samples of sixteen populations of Rattus rattus from southern India, the oldest individuals have less variable molar widths than the younger ones. This is probably due to stabilizing selection by mortality. There is no detectable heterogeneity between sexes or teeth or among populations in this selection. Although there is no average difference between age classes in mean tooth width, the difference between age classes is heterogeneous among populations. This heterogeneity may reflect heterogeneity in directional selection or in direct environmental effects. The selection intensity on the variance is about 0·04.