bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the evolutionary adjustment of spontaneous mutation rates
Authors: Kimura Motoo 
Published: September 2009

Evolutionary factors which tend to decrease the mutation rate through natural selection and those which tend to increase the mutation rate are discussed from the standpoint of population genetics. The author's theory of optimum mutation rate based on the principle of minimum genetic load is re-examined, assuming that mutation rate is adjusted in the course of evolution in such a way that the sum of mutational and substitutional load is minimized. Another hypothesis is also examined that only selection toward lowering the mutation rate is effective and the present mutation rate in each organism represents the physical or physiological limit that may be attained by natural selection.The possibility cannot be excluded that the spontaneous mutation rate is near the minimum that may be attained under the present mode of organization of the genetic material, and at the same time is not very far from the optimum in the sense of minimizing the genetic load.
The limits to artificial selection for body weight in the mouse: III. Selection from crosses between previously selected lines
Authors: Roberts R. C. 
Published: September 2009

1. Four lines selected for large size were crossed to form a base population for further selection for high 6-week weight; three small lines were crossed similarly, and the crossbred population was selected for low 6-week weight.2. In every case, a cross between two selected lines resulted in heterosis increasing body weight. This shows that all of the selected lines were differentiated with respect to genes affecting body weight.3. Further selection for large size produced a stock whose mean weight was 25% higher than the largest of the original lines at its limit. But the response to selection for small size was slow, and after twenty-four generations of selection, the low weights of two of the original lines had not been recovered.4. The evidence points to linkage of genes affecting body weight in the mouse. It is suggested that this is a particular feature of crosses between previously selected lines, rather than a general feature of mouse populations.
The limits to artificial selection for body weight in the mouse: IV. Sources of new genetic variance—irradiation and outcrossing
Authors: Roberts R. C. 
Published: September 2009

1. Two methods are examined of introducing new genetic variance into a line of mice selected for high 6-week weight which, at its limit, displayed no additive genetic variance.2. The first method—irradiation—gave largely negative results. Any further gain under selection that was achieved could not be clearly distinguished from a possible environmental trend.3. The second method—outcrossing to an unselected strain and then selecting from the cross—resulted in a clear gain over the original limit, but nine generations were required even to recover the original limit.4. Various methods of transcending selection limits are evaluated in terms of their application to livestock improvement.
Close linkage between genes which cause hairlessness in the mouse
Authors: Flanagan S. P. , Isaacson J. H. 
Published: September 2009

1. A new semi-dominant gene called shaven (Sha) causes hairlessness in the mouse and it is closely linked to naked. Homozygous shaven mice never grow a first coat and adults grow a few short hairs only. Shaven heterozygotes grow a full coat which is greasy.2. The percentage recombination between shaven and naked was found to be 0·8%. Three-point tests with naked and caracul showed that the order of the three loci is either N–Sha–Ca or N–Ca–Sha.3. The failure of homozygous shaven mice to grow a coat is due to abnormal keratinization of the hairs in the follicles. The follicles were found to be deficient in sulphydryl groups.4. The greasiness of the Sha+ coat is due to the presence of a sudanophilic fluid in the hair medullae.5. The close linkage between the two genes with similar phenotypic effects is discussed.
Effects of X-rays on response to selection for a quantitative character ofDrosophila melanogaster
Authors: Jones L. P. 
Published: September 2009

1. Lines with ten pairs of parents and selected at an intensity of 20% were exposed to 1000 r. of X-rays for 0, 2, 10 or 30 generations.Lines which received some irradiation generally gave greater response than the unirradiated controls. The phenotypic variance in the irradiated lines was much higher than in the controls. There was little difference in behaviour between lines receiving ten generations of irradiation and those irradiated every generation. Lines receiving only two generations of irradiation had lower variances than the other irradiated lines, but in one of three replicates the response was greater than the corresponding continuously irradiated line.3. Lethal frequencies were much higher in irradiated than unirradiated lines. Particular chromosome II and III lethals were at high frequencies in most of the irradiated lines but in only two out of five controls.4. On relaxation, the mean of the irradiated lines generally declined considerably, but in the unirradiated lines there was only a very small regression.5. It appears that most of the extra response and increased variance in the irradiated lines were caused by a few genes with large effect on bristle number.
Developmental genetics of leaf formation in Lolium: 1. Basic Patterns of Leaf Development in L. Multiflorum and L. Perenne
Authors: Edwards K. J. R. 
Published: September 2009

1. Repeated measurements on the growth of individual leaves in seedlings and young plants of ryegrass combined with dissections of the apex of the shoot and of very young leaves have shown that the basic pattern of leaf formation is very similar in Lolium multiflorum and L. perenne.2. The initial growth rate of a leaf primordium is low but increases suddenly at a point when the primordium is somewhat longer than the apex and about 1 mm. in length. After this transition, which I have called the unfolding of the leaf, the rate of elongation is faster and more or less linear until the leaf is nearly mature.3. The time of unfolding of a leaf is very closely associated with the time of maturity of the next older leaf on the same side of the apex. Thus a leaf ceases growth when the next younger leaf immediately above it starts elongating rapidly, though which is cause and which is effect is it not possible to say.4. This close relationship between duration of leaf elongation and rate of unfolding of successive leaves holds for both species in two seasons. It leads one to predict that selection for increased leaf size, in so far as it is a result of greater duration of leaf elongation, is likely to be accompanied by a slower rate of leaf appearance, and conversely that selection for rate of leaf appearance is likely to result in smaller leaves.
Developmental genetics of leaf formation in Lolium: 2. Analysis Of Selection Lines
Authors: Edwards K. J. R. 
Published: September 2009

Detailed measurements of leaf growth and leaf dimensions in the seedling stage were made on lines which had been selected either for large or small leaf size or for fast or slow rates of leaf appearance within one population of Lolium multiflorum (Italian ryegrass) and two populations of L. perenne (Irish perennial and Hunsballe perennial ryegrass).Selection for either character had no effect on the rate of initiation of primordia at the apex, but did change the rate at which successive primordia became leaves. This rate of unfolding was very highly correlated with the rate of visible appearance of leaves and in all cases showed a parallel response to selection for the latter, as did also the rate of maturation of leaves. All three rates showed a negative correlated response to selection for leaf size.Selection for increased leaf size in all cases led to a longer duration of the elongation of an individual leaf, but selection for faster rate of leaf appearance always reduced this duration. The rate of elongation of individual leaves increased under selection for larger leaf size but showed irregular changes under selection for faster leaf appearance, going down in Irish but up in Hunsballe.Data for dimensions of cells from the lower epidermis showed that changes in leaf length under selection were sometimes associated with changes in cell length, some-times in cell number and sometimes with both.Selection had in no case disrupted the close association between the maturation and cessation of growth of a leaf on the one hand, and, on the other, the unfolding from the apex and onset of rapid growth of the next younger leaf on the same side of the apex. Thus in all lines only two leaves (one on each side of the apex) were elongating rapidly at any one time, and an increase in the rate of unfolding was associated with a decrease in the duration of elongation and vice versa.This association was the basis of the observed negative correlated responses between leaf size and rate of leaf appearance. But the fact that the rate of elongation could change independently of the duration opened up the possibility of setting up a selection criterion which would increase the total rate of leaf area formation.The value of this kind of analysis of a character complex in a plant-breeding programme is suggested to lie in discovering physiologically or developmentally limiting processes rather than merely identifying morphological components.
Behavior of three colicine factors and an R (drug-resistance) factor in Hfr crosses inSalmonella typhimurium
Authors: Dubnau Eugenie , Stocker B. A. D. 
Published: September 2009

An LT2 Hfr strain,his metC gal, was crossed to a multiply marked LT2 F−line. Analysis of recombinant yields, segregation of unselected markers and interrupted matings indicated injection of the Hfr chromosome in the sequenceThe introduction into the Hfr of the colicine factorscolI, colE1andcolE2and the R factorR2had little or no effect on its fertility. All four factors were transmitted at low frequency to the F−population, and to recombinants at higher frequencies (colI5–30%,colE130–80%,colE25–30%,R20–9%). Transfer ofcolE1occurred before 20 min., that ofcolE2andcolIlater than 100 min. Segregation data did not reveal close linkage of any factor to any chromosomal locus, but recombinants with a long stretch of donor chromosome were more likely than others to have acquiredcolE2andcolI. Nearly all recombinants andF−cells which acquiredcolIorcolE2acquired both, andcolE1also. Most cells which acquiredR2acquired one or more colicine factors. These plasmid associations can be formally represented by transfer of plasmids, independently of the chromosome, in the sequencecolE1—(colI, colE2)—R2. Phage P22 grown on the Hfr carrying the four plasmids transduced thetet-rtrait ofR2at very low frequency, and thesul-r str-rcharacters, together, at low frequency. Some of each sort of drug-resistance transductant, but no transductants in respect of chromosomal characters, acquiredcolEl or colE2by co-transduction.
Two-way selection for body weight in Tribolium on two levels of nutrition
Authors: Hardin R. T. , Bell A. E. 
Published: September 2009

Parameters necessary for predicting direct and correlated responses for large and small 13-day larval weight in T. castaneum on two levels of nutrition were estimated in the base population. Larval weight in the GOOD environment was approximately twice that observed in POOR. Heritabilities (estimated from the ratio of sire component to total phenotype variance) of larval weight on the two rations were similar, 0·21 ± 0·06 and 0·19 ± 0·05 for GOOD and POOR, respectively. Heritabilities based on dam-offspring covariances were similar to these, but those obtained from full-sib covariances were much larger (0·97 ± 0·07 for GOOD and 0·69 ± 0·07 for POOR). This suggested that considerable dominance rather than maternal effects were present. The genetic correlation between growth on GOOD and growth on POOR was estimated as + 0·60 ± 0·21.The selection experiment was replicated four times with each replication extending over eight generations. Good agreement between predicted and observed values for direct selection was observed for large selection in both environments and small selection in POOR. However, response to small selection in GOOD was significantly greater than predicted in all four replications and was associated with increased selection differentials. Realized heritabilities were approximately the same for both directions in GOOD yet asymmetrical responses occurred for all replications due to unequal selection differentials. On the other hand, realized heritabilities were asymmetrical in POOR. Those observed for small selection were more than twice the size of those calculated for large lines. However, the responses in POOR were symmetrical since the selection differentials varied inversely with the realized heritabilities.Because of the asymmetry observed for heritabilities and selection differentials, correlated responses were poorly predicted. The average effective genetic correlation between growth in GOOD and growth in the POOR environment agreed remarkably well with the base estimate, yet asymmetry of the genetic correlation was a consistent phenomenon with values for the large lines being less than the base parameter while small lines were uniformly larger.Asymmetries of the various genetic parameters were not anticipated from base estimates. They were not caused by sampling or chance fluctuations since all four replications were remarkably consistent. Asymmetry for any one genetic parameter (e.g. heritability) was associated with a particular environment or direction of selection while other genetic parameters reacted asymmetrically in populations exposed to a different set of environmental treatments.For maximum performance in a single environment, these results show that selection should be practiced in that environment. With regard to mean performance in GOOD and POOR environments, selection for large size in POOR gave some 25% more gain than selection in GOOD. Selection for small size in either environment was equally effective in obtaining minimum size in both environments.
Gene action in the mammalian X-chromosome
Authors: Grüneberg Hans 
Published: September 2009

Contrary to opinions expressed by various authors, the phenotype of heterozygotes for mammalian sex-linked genes gives no support for the Lyon hypothesis (L.H.). Evidence, mainly from the mouse, shows that in such heterozygotes, both alleles act together as in autosomal genes.In the present paper, it is shown that neither the behaviour of double heterozygotes for sex-linked genes nor that of X-autosome translocations provides independent evidence in favour of the L.H.: in each case, the interpretation depends on that of the behaviour of single heterozygotes and hence fails to discriminate. Moreover, new facts from both types of situation are also contrary to the L.H. In particular, a unified interpretation which fits the behaviour of genes in all known types of X-autosome translocations in the mouse requires the assumption that partial inhibition of gene action happens in both X-chromosomes of mouse females, and presumably the females of other mammals. The new hypothesis is consistent with all relevant genetical facts and, like the L.H., it also accounts for dosage compensation.
Genetic analysis by means of the parasexual cycle inAspergillus niger
Authors: Lhoas Pol 
Published: September 2009

An investigation of mitotic segregation and recombination inA. nigergave the following results:1. Thirty-one non-allelic markers have been assigned to six linkage groups (containing 11, 9, 6, 3, 1 and 1 markers respectively) by the analysis of haploid mitotic segregants from synthesized diploids.2. The sequence of nine markers in one linkage group was determined and some of the map intervals were estimated by the analysis of haploids, recombinants for linked markers.3. Almost all the haploid segregants were obtained on medium supplemented with the aminoacid analogue,p-fluoro-phenylalanine, the action of which is interpreted as an induction of chromosome losses.4. The rates of mitotic crossing-over and haploidization are much higher than in the sexual speciesA. nidulansand the data support Pontecorvo's (1958) suggestion that the parasexual cycle can be a substantial alternative to the sexual cycle.
The effects of inbreeding on the components of litter size in mice
Authors: McCarthy J. C. 
Published: September 2009

Twenty-four lines were bred from a base population of outbred Q mice by continued full-sib mating. Inbreeding depression in litter size at birth was observed. This decline in litter size was analysed in terms of ovulation rate, the incidence of preimplantation mortality and the incidence of postimplantation mortality. Pregnant females were dissected at 17½ days' gestation and the numbers of corpora lutea, or eggs, and of live and dead embryos were counted. Matings were arranged so that separate estimates of the effects of inbreeding in the mother and in the litter on the components of litter size could be obtained.In the first generation of inbreeding when the inbreeding coefficient of the litter was raised from 0 to 25% decline in litter size was attributable to an increased incidence of preimplantation mortality.In the second and fourth generations decline in litter size was attributable to (1) a reduction in the number of eggs ovulated by the inbred mothers, (2) an increased incidence of preimplantation mortality which resulted from inbreeding in the mother. No evidence of significant effects on mortality of inbreeding in the litter was obtained in the later generation of inbreeding.These findings are discussed in the context of previous work on the effects of inbreeding and crossing on litter size and its components in mice and pigs.
Inversion heterozygosity and selection for wing length inDrosophila subobscura
Authors: Prevosti Antonio 
Published: September 2009

1. Selection for long or short wings was carried out in three pairs of lines of which two were started from the same basic population. At the end of the selection experiment the frequencies of the chromosomal arrangements were determined in each line and compared with the corresponding original frequencies to see if the chromosomal polymorphism ofDrosophila subobscurais related to the genetic variation of size in a regular way.2. The three pairs of lines show an asymmetrical response to selection. Selection for long wings is less effective in changing the mean of the population than selection for short wings.3. Heritability is lower in the lines selected for long wings, especially in the later generations of selection.4. Viability shows a very small decrease during selection in most selected lines.5. In no case does the coefficient of variability show statistically significant changes, but there is a general tendency for it to decrease.6. Selection for long wings favours combinations heterozygous for the standard chromosome orders and specific complex inversion orders. Selection for short wings generally fixes in homozygous combination specific complex inversion orders.7. The heterozygous combinations of the standard chromosomal orders, which are most frequent in northern populations, when combined with the complex inversion orders which are most frequent in southern populations, have a heterotic effect on size.8. The complex inversion orders usually fixed in homozygous combinations in the lines selected for short wings are those most frequent in southern populations which have a smaller mean size than northern populations.9. The blocks of genes integrated in ‘supergenes’ in the inverted segments of the chromosomes ofD. subobscuradiffer in genetic composition with respect to the control of wing length.
A serum esterase variation inMicrotus agrestis(L.)
Authors: Russell M. A. , Semeonoff R. 
Published: September 2009

1. An investigation of the serum esterases of the field-vole,M. agrestis, has been carried out by the method of starch-gel electrophoresis.2. A total of 254 animals, mainly from Carron Valley, near Stirling, have been examined.3. Evidence is presented for a system of four enzymes controlled by two genetic loci, which it is proposed to call Es-3C and Es-3R.4. Each locus specifies one polypeptide sub-unit of the E3enzyme, which is a dimer.5. The two loci each have two alleles present at high frequencies in the population examined.
A comparative genetical study on DDT resistance in adults and larvae of the mosquitoAedes aegyptiL
Authors: Wood R. J. 
Published: September 2009

Inheritance of DDT resistance has been studied in crosses between the highly resistant ‘T’ strain ofA. aegypti(constituted by inbreeding from the TRINIDAD DDT-resistant stock) and the ‘64’ susceptible strain.Larval DDT resistance derives from a major geneRDDT1on linkage group II, the order beingRDDT1–s–y. Linkage group III may also contribute to larval resistance. Linkage group I makes no contribution.Adult DDT resistance derives from a major geneRDDT2, 18·2 ± 2·1 units from the marketblton linkage group III. Linkage group II has no influence on adult resistance.Selection with DDT to retain onlyRDDT1/+ segregants in larvae of backcrossesRDDT1/+×+/+ did not increase resistance in resulting adults, confirming the difference in genetic mechanism at the two stages.The F1progenies from reciprocal crosses between ‘T’ and ‘64’ differed slightly but significantly in larval resistance, modifying the influence of the major geneRDDT1in the heterozygote.The early developmental stages of theRDDT1/+ phenotype (up to the fourth larval stage) were more viable than the +/+ phenotype in backcross segregation. The difference in mortality probably exceeded 30%.
Aromatic amino acid biosynthesis and para-fluorophenylalanine resistance inAspergillus nidulans
Authors: Sinha Umakant 
Published: September 2009

1. Five additional phenylalanine (PHE)-requiring mutants have been isolated but they do not add to the number of loci already known which have been designatedphenA(phen2and its alleles) andphenB(phen6).2. Two pathways for tyrosine (TYR) synthesis inA. nidulanshave been proposed: the well-known one by the transamination ofp-hydroxyphenylpyruvic acid and an alternative one, as in animals, by the hydroxylation of PHE.3. Ten allelic partial TYR-requiring mutants (tyrA), presumably blocked in the transamination pathway, have been isolated after N-methyl-N′-nitro-N-nitrosoguanidine (NTG) treatment ofbil;phenA3 conidia.4. Four partial TYR requirers (at another locus—tyrB) have been isolated after NTG treatment oftyr A7, bi1conidia. They are presumably blocked in an alternative pathway for TYR synthesis, i.e. in the PHE-hydroxylation pathway.5.tyrAmutants have been found to bep-fluorophenylalanine (FPA)-resistant and allelic to mutants at thefpAlocus.tyrBmutants have been found to be very leaky and FPA-sensitive.tyrA;tyrBdouble mutants have been found to be exacting TYR requirers.6. Mutants at locifpA(tyrA) andfpE(anthranilic acid-requiring) have been interpreted to bep-fluorophenylalanine-resistant due to an oversynthesis of PHE.
Genetic control of maturity inTetrahymena pyriformis
Authors: Bleyman Lea K. , Simon Ellen M. 
Published: September 2009

A new mutation,Em, is described forT. pyriformis, syngen 1. This dominant mutation eliminates the normal immature period in heterozygotes but is lethal in the homozygous state.This paper is dedicated to Dr. Ralph Cleland in honor of his 75th birthday.