bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural selection as the process of accumulating genetic information in adaptive evolution
Authors: Kimura Motoo
Published: September 2009

1. In the course of evolution, complicated organisms have descended from much simpler ones. Since the instructions to form an organism are contained in the nucleus of its fertilized egg, this means that the genetic constitution has become correspondingly more complex in evolution. If we express this complexity in terms of its improbability, defining the amount of genetic information as the negative logarithm of its probability of occurrence by chance, we may say that genetic information is increased in the course of progressive evolution, guided by natural selection of random mutations.

2. It was demonstrated that the rate of accumulation of genetic information in adaptive evolution is directly proportional to the substitutional load, i.e. the decrease of Darwinian fitness brought about by substituting for one gene its allelic form which is more fitted to a new environment. The rate of accumulation of genetic information is given by

where Le is the substitutional load measured in ‘Malthusian parameters’.

3. Using Le = 0·199, a value obtained from the application of the ‘principle of minimum genetic load’ (cf. Kimura, 1960 b), we get

It was estimated that the total amount of genetic information accumulated since the beginning of the Cambrian epoch (500 million years) may be of the order of 108 bits, if evolution has proceeded at the standard rate.

Since the genetic information is transformed into phenotypic information in ontogeny, this figure (108 bits) must represent the amount of information which corresponds to the improved organization of higher animals as compared to their ancestors 500 million years back.

4. Problems involved in storage and transformation of genetic information thus acquired were discussed and it was pointed out that the redundancy of information in the form of repetition in linear sequence of nucleotide pairs within a gene may play an important role in the storage of genetic information.
Genetical analysis of methionine suppressors in Coprinus
Authors: Lewis D.
Published: September 2009

Seven different genes, me-1 to me-7, controlling the steps in the synthesis of methionine in the Basidiomycete Coprinus lagopus have been tested for the production of prototrophs on minimal medium. Cultures carrying me-1 and me-7 produced prototrophs spontaneously at a rate of 2·6 × 10−5. These prototrophs were the result of mutations of suppressor genes and not due to back-mutation of the me-gene.

An intensive study of sixty-four mutants of an independent origin suppressing me-1 has revealed five different suppressor loci.

Tests for complementation between suppressor mutants and for their recessiveness to the wild allele were made in dikaryons.

All suppressor mutants were recessive to the wild allele. The five suppressor loci were all separated from one another by recombination, twenty-eight map units being the smallest distance between any two pairs. Mutants of the same locus did not complement one another, with few exceptions. Mutants of different loci, as tested in the trans-position in a dikaryon, complemented one another with the exception of pairs between sup-3, sup-4, and sup-5. Sup-3 and sup-4 are 28 units apart and are independent of sup-5 and yet they did not complement. This unique example of long-distance non-complementation is discussed in terms of gene action.
On the distribution of recessive embryonic lethals in a natural population ofCoelopa frigida(Fab.)
Authors: Burnet B.
Published: September 2009

An account is given of the habitat and ecology of a wrackbed population ofCoelopa frigida(Fab.). The spatial distribution of the third-instar larvae was found to be patchy. This is due to a preference of adult flies for oviposition sites in zones of high temperature within the wrackbed. The relationship between larval density and temperature was found to account only in part for the patchy distribution, a second factor being the formation of family aggregates within each temperature zone. The effect of this type of spatial distribution on the interpretation of genetic sampling methods for the population is discussed.

Samples of third-instar larvae from the wrackbed population have been analysed for the presence of recessive embryonic lethals in three consecutive years from 1957 to 1959. From a total of 528 gametes tested, 44 recessive embryonic lethals were isolated. Cross tests for allelism showed that certain lethals were repeated within samples taken in the same year.

The gross frequency of embryonic lethals is shown to be independent of seasonal changes in population density. Estimates of gene frequency are made for certain individual lethals and these are shown to be greater than expected on the basis of the census size of the population. Possible causes of this discrepancy are examined.
Nutritional requirements of inbred lines and crosses ofDrosophila melanogaster
Authors: Sang James H.
Published: September 2009

1. The problem of whether or not hybrids are more efficient, less variable and have less stringent nutritional needs than their parents is examined by finding the dose-responses of four inbredDrosophilalines and their crosses to casein, choline, RNA, riboflavine, nicotinic acid, pyridoxine and folic acid, under germ-free conditions.

2. Under more or less optimal conditions, survival, development rate and weight of the hybrids are generally superior to those of the inbreds; the 4-way cross is not inferior to the 2-way crosses. Variability of the crosses is not necessarily lower than that of the inbreds, and the 4-way cross is no more variable than the 2-way crosses.

3. As measured by growth rate, the hybrids use casein more effectively than the pure lines, but their relative efficiency declines as the casein supply is decreased. There is a positive correlation between casein requirements for optimal growth and minimum requirements of pyridoxine. Hybrids also tend to be more efficient in their use of choline, but not of the other nutrients examined.

4. Deficiencies of particular nutrients (and also of excess provision of the non-vitamins) affect the lines and crosses differently, so that their relationships to one another are altered. The hybrids show no special advantage in resisting departures from the optimum. Variability is also changed significantly under sub-optimal conditions and, in some situations, the hybrids may then be more variable than the inbreds.

5. Each line and each cross is found to have its own optimal nutritional environment, and its particular reactions to departure from this. The full potential of the genotypes cannot be manifest, therefore, by tests in a single, standard environment.
The effect of initial reverse selection upon total selection response
Authors: Allan J. S. , Robertson Alan
Published: September 2009

A computer has been used to investigate the effect of an initial period of reverse selection on the subsequent response of a population to renewed forward selection with the same population size and selection intensity. As the computer was used to derive gene frequency distributions, there was no random element in the results obtained. A theoretical solution to the problem was obtained for genes with small effects.

The process can be adequately described by the duration of the reverse selection (expressed in terms of the population sizeN), the product of population size and gene effect,Ns, and the initial gene frequency. If the duration of reverse selection,t, is less thanN/2, the loss in selection advance due to the reverse selection is roughlyt/N, though slightly greater than this for genes with low frequency. The ‘point of no return’ after which it is impossible, with the same population size and selection intensity, to return even to the starting frequency is 1·4Ngenerations for genes with small effect and this declines as the gene effect increases.

Some extension of results to recessive genes is also given.
The parasexual cycle inVerticillium albo-atrum
Authors: Hastie A. C.
Published: September 2009

Genetic recombination through the parasexual cycle, or some very similar system, was demonstrated. Diploid strains were very unstable, yielding about 95% haploid conidia from three-week-old cultures This high frequency of haploid segregants was at least partly attributable to greater sporulation of haploid mycelium, but may also reflect a higher frequency of haploidization than that found inAspergillus nidulans.

Mitotic crossing-over also occurred frequently, and gave segregants homozygous for some markers but heterozygous for others. It was also detectable by changes in the phase of linked markers occurring during vegetative growth. Some heterozygous segregants were either aneuploids, or were formed by double mitotic crossovers.

Haploid segregants, derived from nuclei which had previously undergone mitotic crossing-over, were often recovered. This coincidence of mitotic crossing-over and haploidization in one nuclear lineage, together with the probable occurrence of double mitotic crossovers, makes mitotic analysis less clear cut than inAspergillus nidulans.
On one of the formulae proposed for interpreting transduction data
Authors: Dawson G. W. P.
Published: September 2009

The paper on the analysis of data from transduction experiments with Salmonella typhimurium, which was published in Genetical Research (Dawson, 1963), unfortunately contained an error on p. 419. In calculating the limiting values X/Y, the formulae for d and d′ are correctly stated, but their solutions are transposed. The last and third last lines on p. 419 should therefore be interchanged. In the arithmetic example on pp. 420 and 421, a similar interchange of the calculations of d and d′ is necessary. The maximum value of a/b is then:

and the calculation of the minimum value should be:

These values of 2·20 and 1·23 are to be compared with the values of 2·23 and 1·24 in the published paper.
Hyphal fusions in the wood-rotting fungusSchizophyllum commune: I. The effects of incompatibility factors
Authors: Ahmad Sayed S. , Miles Philip G.
Published: September 2009

Effects of the incompatibility factors inSchizophyllum communeFries on the process of hyphal fusion are described. A role for the A incompatibility factor in hyphal fusion is indicated. Matings between strains with different mating types have higher fusion frequencies than matings between strains with the same mating types. Evidence is presented that the differences in fusion frequencies are not due to genetical factors other than mating types. When two strains of different mating types are grown in the same culture plate, but separated by a cellophane membrane, the strains are altered in some unexplained manner in such a way that even matings between strains of the same mating type have a higher fusion frequency than occurs in matings between compatible strains not so treated. Matings leading to the formation of common-B and dikaryotic mycelia have comparable fusion frequencies while those leading to the formation of common-A mycelia have a far lower frequency of fusions. It has been demonstrated that high fusion frequency is associated with heterozygosity at the A locus. It is suggested that a repression–derepression mechanism involving a cell wall degrading enzyme or enzymes may be involved in the regulation of hyphal fusion.
Lethal interactions of theeye-goneandeyelessmutants inDrosophila melanogaster
Authors: Hunt David M.
Published: September 2009

A synthetic lethal system involving homozygous combination of the non-allelic eye mutantseye-goneandeyelessis described. The major lethal crisis is towards the end of the pupal instar although a number of double homozygotes die at pupation. The pupal lethal crisis can be overcome in a number of individuals by the experimental removal of the operculum from differentiated pupae. However, only a few of the resulting enclosed double homozygotes proved fully viable, the remainder dying almost immediately after emergence. Dissection of the surviving adults revealed that the brain is located in the anterior thorax.
Gene conversion: observations on the DNA hybrid models
Authors: Paszewski Andrzej
Published: September 2009

Some features of gene conversion in fungi and their bearing on the hybrid DNA models are discussed. Available experimental data from tetrad analysis seem to give a more complex picture of polarity in intra-genic recombination and of the relations between conversion and post-meiotic segregation, and between conversion and crossing-over, than predicted by the models.

A new hypothesis of the mechanism of gene conversion with special attention given to the aspect of asymmetry in this phenomenon is proposed as an alternative to the mechanism suggested by the DNA hybrid models.
Variations in enzyme phenotypes and their underlying genotypes among wild strains of the genusNeurospora
Authors: Grindle M. , Davis R. H.
Published: September 2009

Twenty-three exotic strains of four species ofNeurospora(N. crassa, N. sitophila, N. intermediaandN. tetrasperma) were grown in minimal medium and their enzyme phenotypes were compared. The exotic strains did not differ substantially with respect to the specific activities of the biosynthetic enzymes, ornithine transcarbamylase (OTC), carbamyl phosphokinase and aspartate transcarbamylase. Exotic strains ofN. crassaandN. sitophilawere crossed with laboratory mutants ofN. crassato determine whether there were significant differences among the exotic strains in the gene complexes underlying their enzyme phenotypes. Most of the exotic strains carried similar OTC structural genes and similar genetic modifiers of OTC activity: their OTC structural genes were expressed normally in the genomes of the parent strains, in the alien genomes of standard laboratory mutants and in the mixed genomes of parent × mutant hybrids. One exoticN. crassacarried a distinctive OTC structural gene that elevated OTC activity when transferred into the genome of a standard laboratory mutant. A second exoticN. crassacarried distinctive genetic modifiers of OTC activity: two mutations,c-andhi, interacted in the exotic parent to normalize OTC activity and rate of growth, buthiled to extremely high OTC activities and to a reduction in rate of growth when separated fromc-by interstrain recombination.
The length of time required for a selectively neutral mutant to reach fixation through random frequency drift in a finite population
Authors: Kimura Motoo
Published: September 2009

Frequency distribution of the length of time until fixation (excluding the cases of eventual loss) of a selectively neutral mutant in a finite population was obtained. With 4Negenerations (Ne, effective population size) as the unit length of time, the distribution has mean μ1= 1, standard deviation σ = 0·538, skewness γ1= 1·67 and kurtosis γ2= 4·51 (see Fig. 1).
A genetic study of cold resistance in wheat
Authors: Law C. N. , Jenkins G.
Published: September 2009

The variety Chinese Spring ofTriticum aestivumis susceptible to cold treatment applied at the juvenile plant stage, while the variety Cappelle-Desprez shows resistance to such treatment. By cytological and backcross procedures single homologous pairs of chromosomes from Cappelle-Desprez were substituted for their homologues in Chinese Spring. Assay experiments carried out on each of the 21 possible substitution lines indicated that three chromosomes, 4D, 5D and 7A of Cappelle-Desprez were involved in the determination of cold resistance. The resistance expressed by the three substitution lines carrying these chromosomes was less than the reaction of Cappelle-Desprez to cold treatment. Also the magnitude of this resistance supported a hypothesis that the action of the three chromosomes was additive on the scale of measurement used. The possible relationships of the genes for cold resistance to the established genes controlling other developmental characters, also carried by these three chromosomes, are discussed.
The reduction in fitness from genetic drift at heterotic loci in small populations
Authors: Robertson Alan
Published: September 2009

In finite populations, loci maintained segregating by hétérozygote superiority will be disturbed from their equilibrium positions by genetic sampling and the mean fitness of individuals will consequently be reduced. A general expression for this reduction is obtained for the segregation of two alleles. If the probability of continued segregation at the locus is high, the reduction tends to 1/4N, irrespective of the strength of selection, whereNis the effective population size. This will always be much less than the segregation load. Ifnalleles are segregating, so that all heterozygotes have the same fitness, the reduction tends to (n−1)/4N.
Selection for a threshold character inDrosophila: III. Genetic control of variability in plateaued populations
Authors: Latter B. D. H.
Published: September 2009

An analysis of populations ofDrosophila melanogasterwhich had ceased to respond to selection for increased scutellar bristle number has disclosed the existence of an overall negative genetic correlation between replicate lines in the frequency of the two major component bristle types, viz. anteriors and posteriors. Negative phenotypic correlations among component bristle sites have also been detectedwithinpopulations. A model involving competition among sites for the available resources of a particular limiting substrate is therefore proposed. Genetic changes have been effected in exceptional populations which lead either to an increase in the rate of production of the limiting substrate, or to a lowering of the concentration of the substrate necessary for bristle initiation. The allelic substitutions concerned are recessive, and have been described asdecanalizingalleles in view of their effects on both bristle number variability and a measure of developmental regulation at individual anterior sites. Genetic variation has also been demonstrated for the mean allocation of resources to each of the four component bristle types, viz. anteriore interstitials, posteriors and apicals. A brief discussion is given of the implications of the model for breeding practice in domestic species.
A system generating spontaneous intrachromosomal changes at mitosis inAspergillus nidulans
Authors: Nga B. H. , Roper J. A.
Published: September 2009

Previous studies had shown that haploid strains ofAspergillus nidulanswhich have a chromosome segment in duplicate are unstable at mitosis. Through the study of various haploid and diploid strains, with and without translocations and with balanced and unbalanced genomes, it has been shown: (1) that imbalance of chromosome segments is responsible for instability, and (2) that the chromosomal deletions produced are confined solely or largely to the segments which provoke instability.

The term ‘mitotic non-conformity’ has been proposed for this instability phenomenon. An explanation for it has been sought in terms of attachment sites, limited in number and specific for chromosome segments, at which replication is initiated.
Genetic polymorphism and interspecific competitive ability inDrosophila
Authors: Ayala Francisco J.
Published: September 2009

A simple method is given to compare the relative fitnesses of various populations of one species when they compete with another species. Populations ofDrosophila psevdoobscurapolymorphic for the chromosomal inversions CH and AR are superior to monomorphic populations CH or AR when they compete for the available resources withD. serrata.
Effect of inhibition of DNA synthesis on u.v. sensitive Bs strains ofEscherichia coli
Authors: Green Michael H. L. , Donch John , Chung Young S. , Greenberg Joseph
Published: September 2009

The effect of nalidixic acid, a specific inhibitor of DNA synthesis, onEscherichia colistrain B (lon) and its u.v.-sensitive derivatives is examined. Strain B itself is sensitive to nalidixic acid, whereas its u.v.-resistant derivative B/r is resistant.

It is shown that in allexr Astrains, in which u.v.-induced filamentation is suppressed, resistance to nalidixic acid is increased. Amongexr Astrains, Bs4 is exceptionally resistant to nalidixic acid. This is because nalidixic acid kills only growing cells and strain Bs4, atryauxotroph, may grow poorly under the conditions used to test nalidixic acid.

Theuvrgenes of the HCR strains Bs1, Bs8 and Bs12 do not suppress u.v.-induced filamentation nor do they affect the response to nalidixic acid. Theuvrgene of strain Bs3 is unusual in increasing the tendency to filament and also sensitivity to nalidixic acid.

Strains Bs1, Bs3 and Bs8 are all doubly mutated from strain B, the second mutation (notuvr) being responsible for their increased resistance to nalidixic acid as well as partially or completely suppressing filamentation.

It is concluded that the cell division mechanism of (lon) strain B is sensitive to inhibition of DNA synthesis. Mutations which suppress the tendency of strain B to filament reduce its sensitivity to inhibition of DNA synthesis.
The induction of gene mutation and chromosome aberration inChlamydomonas eugametosby a phenylalanine analog
Authors: McBride A. C. , Gowans C. S.
Published: September 2009

Evidence is presented which indicates that the phenylalanine analog 2-amino-3-phenylbutanoic acid (APBA) induces mutation to APBA, streptomycin, and neamine resistance in the green algaChlamydomonas eugametos. Apparent chromosome abnormalities (reciprocal translocations and inversions) were also found among some clones recovered after APBA treatment. The two, mutation and chromosome aberration, are separable.
Chromosomal basis of dosage compensation inDrosophila: I. Cellular autonomy of hyperactivity of the maleX-chromosome in salivary glands and sex differentiation
Authors: Lakhotia S. C. , Mukherjee A. S.
Published: September 2009

Morphology and the rate of RNA synthesis of theX-chromosome inXX/XOmosaic larval salivary glands ofDrosophila melanogasterhave been examined. For this purpose the unstable ring-Xwas utilized to produceXXandXOnuclei in the same pair of glands. The width of theX-chromosome and the left arm of the 3rd chromosome (3L) of larval salivary glands was measured and the rate of RNA synthesis by them was studied upon the use of [3H]uridine autoradiography in suchXX(female) andXO(male) nuclei developing in a female background (i.e. otherwise genotypicallyXX). In such mosaic glands the width of the singleX-chromosome of male nuclei is nearly as great as that of the paired twoX's of female nuclei, as is also the case in normal male (X Y) and female (XX). The singleXof male nuclei synthesizes RNA at a rate equal to that of the paired twoX's of female nuclei and nearly twice that of an unpairedXofXXnuclei. Neither the developmental physiology of the sex nor the proportion ofXOnuclei in a pair of mosaic salivary glands of anXXlarva has any influence on these two characteristics of the maleX-chromosome.

It is suggested that dosage compensation inDrosophilais achieved chiefly, if not fully, by a hyperactivity of the maleX, in contrast to the singleXinactivation in female mammals, that this hyperactivity of the maleXis expressed visibly in the morphology and metabolic activity of theX-chromosome in the larval salivary glands of the male, and that this hyperactivity and therefore dosage compensation inDrosophilain general is not dependent on sex-differentiation, but is a function of the doses of theX-chromosome itself.
Correlated meiotic and mitotic maps inAspergillus amstelodami
Authors: Lewis L. A.
Published: September 2009

Thirteen markers inAspergillus amstelodamiwere mapped through meiotic and mitotic recombination, resulting in good correlation of the two linkage groups established by each method. Mapping via mitotic analysis proved the more efficient of the methods because of the long distances between some of the markers established in this organism.

Visual selection of haploid segregants from mitotic recombination was aided by the ability to recover conidia which differed in colour from the haploid parents. These contained pairs of conidial colour markers which were not epistatic to each other.
Mitotic non-conformity inAspergillus: successive and transposable genetic changes
Authors: Azevedo J. L. , Roper J. A.
Published: September 2009

Strains ofAspergillus nidulanswith, a duplicate chromosome segment are mitotically unstable; in addition to phenotypically improved variants, arising following deletions in either duplicate segment, they give morphologically deteriorated types, some with, enhanced stability. In one isolate, deterioration and increased instability were determined by mutation in a duplicate segment; a more stable derivative no longer had this mutation but had one in another linkage group. Another variant, too unstable for analysis, gave derivatives whose single, new mutations were in different linkage groups. It is proposed that deterioration and increased instability result from tandem duplications on either duplicate segment; transposition of these to non-duplicated regions reduces instability. Another 17 variants had a single new mutation each; mutations, possibly clustered, occurred in all linkage groups. In these strains perhaps transposition preceded analysis. Deteriorated variants gave lineages of types with morphological changes caused by further, superimposed mutations. This continued instability is explained as interaction, in fidelity of replication, of non-homologous chromosome segments.

Instability inA. nidulansstems from chromosome imbalance. As imbalance is known or suspected in other cases of instability it may be possible to show common mechanisms for apparently diverse phenomena.
Genetic loads at a polymorphic locus which is maintained by frequency-dependent selection
Authors: Kimura Motoo , Ohta Tomoko
Published: September 2009

If a polymorphic locus is maintained in finite populations by frequency-dependent selection with selective neutrality at equilibrium, it is generally accompanied by two genetic loads, i.e. the dysmetric and the drift loads. The former arises because the fitness of the population may not be at a maximum at the equilibrium gene frequency and the latter because genetic drift in small populations displaces the gene frequency from its equilibrium value.

In some simple models of frequency-dependent selection considered, the drift load is independent of selection coefficients and is approximately equal to (n−1)/(2Ne), wherenis the number of alleles andNeis the effective population size.
Transfer characteristics of two resistance determinants in a wild strain ofKlebsiella aerogenes(V9A)
Authors: Reeve E. C. R.
Published: September 2009

Klebsiella aerogenesstrain V9A carries determinants AKand TK, giving resistance to ampicillin and tetracycline, and a plasmid FKlac, but no active sex factor. F− and I-type sex factors were able to transfer TKfrom V9A toEscherichia coliK12 and between strains of K12, and TKbehaved as a separate plasmid with its own replicon. AKcould not be transferred, except possibly by a sex factor carrying its own A determinant, but the evidence for such transfer was inconclusive. It is suggested that AKis either a chromosomal gene or is in a plasmid with a cell attachment inKlebsiellanot represented inE. coliK12. AKproduces a β-lactamase.
Derepression of F-lacinSalmonella typhimuriumby a determinant for kanamycin resistance
Authors: Smith H. R. , Grindley June N. , Grindley N. D. F. , Anderson E. S.
Published: September 2009

When a determinant for neomycin-kanamycin resistance (K) was transferred by an F-lacfactor intoSalmonella typhimurium, the resulting KF-lacstrain was sensitive to the male-specific phage μ2and F-lacwas derepressed. However, F-lacalone is repressed inS. typhimurium. When kanamycin resistance is spontaneously lost fromS. typhimuriumKF-lacan element persists which derepresses F-lacinS. typhimurium. The results are consistent with the hypothesis that a locusder, for derepression of F-lacinS. typhimurium, lies on the K plasmid. The R factor Rldrd19 is derepressed in K12 but is repressed inS. typhimurium. It also is derepressed byder. In contrast to F-lacand R1, another R factor, R136drdH8, is derepressed in both K12 andS. typhimurium, so that the intervention ofderis unnecessary for its derepression in the salmonella host.
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.
Exclusion, superinfection immunity and abortive recombinants in I + × I + bacterial crosses
Authors: Meynell G. G.
Published: September 2009

I + × I + crosses were studied, using various Coll plasmids. Exclusion due to presence of Coll in recipients was removed by starvation, with production of I – phenocopies. Superinfection immunity prevented normal replication of transferred genes: thus,Itrp+ donated to an I +trp– recipient led to formation of abortive recombinants.
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.
The estimation of generation interval in experimental populations ofDrosophila
Authors: Barker J. S. F.
Published: September 2009

A method for the experimental estimation of generation interval is presented together with results obtained at 25° C. forD. melanogasterOregon-R-C maintained in population cages and in population bottles, and forD. simulans vin population bottles. Although there is significant variation between the replicate estimates obtained in population bottles, and although a number of potential sources of error have been discussed, it is suggested that this method provides useful operational estimates of the parameter, which may be taken as 23 days forD. melanogasterOregon-R-C in population cages, 14 days for the same stock in population bottles, and 16 to 18 days forD. simulans vin population bottles.
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.
Test for sex-linked lethals in irradiated mice
Authors: Auerbach C. , Falconer D. S. , Isaacson J. H.
Published: September 2009

Tabby males were irradiated with 500 r and mated toBn Mobr♀♀. Daughters conceived during the first 3 weeks after irradiation were tested for the presence of sex-linked recessive mutations in their progeny, each daughter representing one irradiated gamete. One visible, but no lethal, was found in theBn–Mobrsegment among 154 tested gametes; one gamete was proved free of lethals or visibles in theBn–Tasegment, and 21 gametes in theTa–Mobrsegment. Among the whole 176 tested gametes there was no indication of a lethal in the adjoining segments.
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.
Non-additive combining abilities
Authors: Gilbert Neil
Published: September 2009

An additive-multiplicative model is found to describe diallel cross data rather well. Estimates of the model's parameters are highly correlated from generation to generation.
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.
Non-disjunction and maternal age inD. melanogaster
Authors: Kelsall P.
Published: September 2009

The frequencies of non-disjunction at first and second meiotic division, in both male and female ofDrosophila melanogaster, are estimated. Numbers of exceptional individuals scored in several broods of increasing parental age are also presented. These results fail to show any evidence of an age-effect. Work claiming to demonstrate the existence of an age effect inDrosophilais reinvestigated. The importance of these results and their relevance to human studies are discussed.
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 induction of dominant lethal mutations in rats by alkane sulphonic esters
Authors: Partington M. , Jackson H.
Published: September 2009

Sterility resulting from treatment of male rats with methyl ethane sulphonate and ethyl methane sulphonate was found to be due to the induction of dominant lethal mutations in spermatozoa and spermatids. Spermatids in the acrosome phase of development were found to be the most sensitive cells and at low doses of both compounds the majority of deaths occurred after implantation. The earlier cell stages, i.e. spermatogenia and spermatocytes, were the most sensitive to isopropyl methane sulphonate and Busulphan (Myleran). The action on spermatogonia was confirmed by spermatid counts and the time of occurrence of oligospermia or aspermia was calculated. Pre-implantation deaths occurred mainly in the early cleavage stages after both isopropyl methane sulphonate and Busulphan; at least part of these losses can be attributed to the induction of dominant lethal mutations in spermatocytes and early spermatids. Isopropyl methane sulphonate appears to be the more effective of the two drugs in this respect.
The genetics of bacterial blight resistance in cotton Further evidence on the gene B6m
Authors: Saunders J. H. , Innes N. L.
Published: September 2009

A study of the gene B6m, previously described as a modifier, revealed that it is a recessive resistance gene of moderate effect when homozygous. Its value in enhancing resistance to bacterial blight when in combination with other genes, in particular B2, is emphasized. The symbol for the gene is simplified to B6.
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.
Quantitative genetic analysis inPhalaris tuberosaI. The statistical theory of open-pollinated progenies
Authors: Latter B. D. H.
Published: September 2009

The present series of papers is concerned with the variation shown by date of ear emergence, seed weight, and measures of seedling growth rate in the Australian Commercial population ofPhalaris tuberosaL. In this first communication, the statistical theory necessary for the interpretation of the available experimental observations is developed. The treatment involves a consideration of the effects of partial self-fertilization under open-pollination, of phenotypic assortative mating, and of maternal effects, on the expectations of the observed covariances among relatives.