bluuebunny/crossref_metadata_2025_split huggingface dataset:
Background selection and patterns of genetic diversity inDrosophila melanogaster
Authors: Charlesworth Brian 
Published: September 2009

SummaryTheoretical models of the effects of selection against deleterious mutations on variation at linked neutral sites (background selection) are used to predict the relations between chromosomal location and genetic variability at the DNA level, inDrosophila melanogaster. The sensitivity of the predictions to variation in the mutation, selection and recombination parameters on which they are based is examined. It is shown that many features of the observed relations between chromosomal location and level of genetic diversity inD. melanogastercan be explained by background selection, especially if the weak selective forces acting on transposable elements are taken into account. In particular, the gradient in diversity in the distal portion of the X chromosome, and the lack of diversity on chromosome 4 and at the bases of the major chromosomes, can be fully accounted for. There are, however, discrepancies between predicted and observed values for some loci inD. melanogaster, which may reflect the effects of forces other than background selection.
The effect of population size on effective population size: an empirical study in the red flour beetleTribolium castaneum
Authors: Pray Leslie A. , Goodnight Charles J. , Stevens Lori , Schwartz James M. , Yan Guiyun 
Published: September 2009

SummaryDespite the increasing number of studies on the magnitude ofNe/Nratios, much remains unknown about the effects of demographic and environmental variables onNe/N. We determinedNe/Nfor seven population size treatments, ranging fromN= 2 toN= 960, in the red flour beetle Tribolium castaneum.Ne/Ndecreased with increasingN, as evidenced by a significant negative relationship between logNandNe/N. Our results are consistent with other published data on the relationship betweenNe/NandN. Effective population sizes in large populations may be much smaller than previously recognized. These results have important implications for conservation and evolutionary biology.
Doublefoot: a new mouse mutant affecting development of limbs and head
Authors: Lyon Mary F. , Quinney R. , Glenister P. H. , Kerscher S. , Guillot P. , Boyd Y. 
Published: September 2009

SummaryThe mutant doublefoot, Dbf, of the mouse arose spontaneously, and was shown to be inherited as an autosomal dominant, mapping 9–13 cM proximal to leaden, ln, on chromosome 1 and showing no recombination with the microsatellite markers D1Mit24 and D1Mit77. In heterozygotes the phenotype includes many extra toes on all four feet, and the tibia and fibula may be reduced and bowed. The head is shortened and broad and the eyes are held half-closed, and some animals develop hydrocephalus. The tail is kinked and abnormally thick, and the soles of the feet are swollen. Growth is retarded, viability is reduced, and reproduction is impaired in both sexes. Only about 30 % of males are normally fertile, and testis weights and sperm counts may be reduced, although this appears not to be the main cause of poor fertility. In females vaginal opening is delayed and oestrous cycles are irregular, although the animals appear to respond to gonadotrophic hormones. Crosses of Dbf/ + × Dbf/ + are very poorly fertile. Prenatally, Dbf/ + heterozygotes can first be recognized at 11½ days gestation by abnormally broad fore limb buds. Putative Dbf/Dbf homozygotes at 12½ days have similar limbs defects and also split face, due to failure of the maxillae to fuse in the midline. Some homozygotes and a few putative heterozygotes have cranioschisis. At 13½ days, the heads of homozygotes tend to bulge in the frontal region and a bleb of clear fluid is visible medially. At 14½ days Dbf/Dbf fetuses may have oedema and some are dead. From 15½ days onwards no live Dbf/Dbf fetuses have been found. The gene maps close to the locus of Pax3, but crossovers between Dbf and Pax3 have been found, ruling out the possibility that a gain-of-function mutation in Pax3 might be involved.
Deviation from Hardy–Weinberg proportions in finite populations
Authors: Wang Jinliang 
Published: September 2009

SummaryFor a finite diploid population with no mutation, migration and selection, equations for the deviation of observed genotype frequencies from Hardy–Weinberg proportions are derived in this paper for monoecious species and for autosomal and sex-linked loci in dioecious species. It is shown that the genotype frequency deviation in finite random-mating populations results from the difference between the gene frequencies of male and female gametes, which is determined by two independent causes: the gene frequency difference between male and female parents and the sampling error due to the finite number of offspring. Previous studies have considered only one of the causes and the equations derived by previous authors are applicable only in the special case of random selection. The general equations derived here for both causes incorporate the variances and covariances of family size and thus they reduce to previous equations for random selection. Stochastic simulations are run to check the predictions from different formulae. Non-random mating and variation in census size are considered and the applications of the derived formulae are exemplified.
Modifiers of mutation-selection balance: general approach and the evolution of mutation rates
Authors: Kondrashov Alexey S. 
Published: September 2009

SummaryA general approach is developed to estimate secondary selection at a modifier locus that influences some feature of a population under mutation-selection balance. The approach is based on the assumption that the properties of all available genotypes at this locus are similar. Then mutation-selection balance and weak associations between genotype distributions at selectable loci and the modifier locus are established rapidly. In contrast, changes of frequencies of the modifier genotypes are slow, and lead to only slow and small changes of the other features of the population. Thus, while these changes occur, the population remains in a state of quasi-equilibrium, where the mutation-selection balance and the associations between the selectable loci and the modifier locus are almost invariant. Selection at the modifier locus can be estimated by calculating quasiequilibrium values of these associations. This approach is developed for the situation where distributions of the number of mutations per genome within the individuals with a given modifier genotype are close to Gaussian. The results are used to study the evolution of the mutation rate. Because beneficial mutations are ignored, secondary selection at the modifier locus always diminishes the mutation rate. The coefficient of selection against an allele which increases the mutation rate by υ is approximately υδ2/[U(2−ρ)] = υŝ, where υ is the genomic deleterious mutation rate, δ is the selection differential of the number of mutations per individual in units of the standard deviation of the distribution of this number in the population, ρ is the ratio of variances of the number of mutations after and before selection, and ŝ is the selection coefficient against a mutant allele in the quasiequilibrium population. However, the decline of the mutation rate can be counterbalanced by the cost of fidelity, which can lead to an evolutionary equilibrium mutation rate.
Effective population size/adult population size ratios in wildlife: a review
Authors: Frankham Richard 
Published: September 2009

SummaryThe effective population size is required to predict the rate of inbreeding and loss of genetic variation in wildlife. Since only census population size is normally available, it is critical to know the ratio of effective to actual population size (Ne/N). Published estimates ofNe/N(192 from 102 species) were analysed to identify major variables affecting the ratio, and to obtain a comprehensive estimate of the ratio with all relevant variables included. The five most important variables explaining variation among estimates, in order of importance, were fluctuation in population size, variance in family size, form ofNused (adults υ. breeders υ. total size), taxonomic group and unequal sex-ratio. There were no significant effects on the ratio of high υ. low fecundity, demographic υ. genetic methods of estimation, or of overlapping υ. non-overlapping generations when the same variables were included in estimates. Comprehensive estimates ofNe/N(that included the effects of fluctuation in population size, variance in family size and unequal sex-ratio) averaged only 0·10–0·11. Wildlife populations have much smaller effective population sizes than previously recognized.
A genetic linkage map for the domesticated silkworm,Bombyx mori, based on restriction fragment length polymorphisms
Authors: Shi Jinrui , Heckel David G. , Goldsmith Marian R. 
Published: September 2009

SummaryWe present data for the initial construction of a molecular linkage map for the domesticated silkworm,Bombyx mori, based on 52 progeny from an F2 cross from a pair mating of inbred strains p50 and C108, using restriction fragment length polymorphisms (RFLPs). The map contains 15 characterized single copy sequences, 36 anonymous sequences derived from a follicular cDNA library, and 10 loci corresponding to a low copy number retrotransposon, mag. The 15 linkage groups and 8 ungrouped loci account for 23 of the 28 chromosomes and span a total recombination length of 413 cM; 10 linkage groups were correlated with established classic genetic maps. Scoring data from Southern blots were analysed using two Pascal programs written specifically to analyse linkage data in Lepidoptera, where females are the heterogametic sex and have achiasmatic meiosis (no crossing-over). These first examine evidence for linkage by calculating the maximum lod score under the hypothesis that the two loci are linked over the likelihood under the hypothesis that the two loci assort independently, and then determine multilocus linkage maps for groups of putatively syntenic loci by calculating the maximum likelihood estimate of the recombination fractions and the log likelihood using the EM algorithm for a specified order of loci along the chromosome. In addition, the possibility of spurious linkage was exhaustively tested by searching for genotypes forbidden by the absence of crossing-over in one sex.
Allelic variation at the Gli-A1m, Gli-A2m and Glu-A1m loci and breadmaking quality in diploid wheat Triticum monococcum
Authors: Saponaro C. , Pogna N. E. , Castagna R. , Pasquini M. , Cacciatori P. , Redaelli R. 
Published: September 2009

SummaryFifty-six accessions of Triticum monococcum and one accession each of T. beoticum and T. sinskajae were analysed for their storage protein compositions and breadmaking quality as determined by the SDS-sedimentation test. In total 30 different alleles at the Glu-A1m locus coding for high-molecular-weight glutenin subunits (HMW-GS), 25 alleles at the Gli-A1m locus coding for ω- and γ-gliadins and 45 alleles at the Gli-A2m locus controlling the synthesis of α/β-gliadins were detected. Most accessions contained one x-type and one y-type HMW-GS and two genotypes were null for both types of subunits. Two polypeptides within the mobility range of HMW-GS in SDS-PAGE were shown to be ω-type gliadins encoded by genes on the short arm of chromosome 1 A. T. sinskajae and several ‘monococcum’ accessions were shown to share the same alleles at Gli-A1m, Gli-A2m and Glu-A1m, confirming sinskajae as a subspecies of T. monococcum. The SDS-sedimentation volumes of most accessions were very low (11–35 ml), a few accessions showing mean sedimentation volumes as high as 90–93 ml. Through the comparison between biotypes occurring in some accessions of ‘monococcum’, good bread-making quality was found to be associated with the presence of alleles y, c and i at the Gli-A1m locus. All accessions were resistant to leaf rust and rich in protein (≥ 16·5%), and most of them showed resistance to powdery mildew.
Chloride channel 2 gene (Clc2) maps to chromosome 16 of the mouse, extending a region of conserved synteny with human chromosome 3q
Authors: Lengeling Andreas , Gronemeier Monika , Ronsiek Melanie , Thiemann Astrid , Jentsch Thomas J. , Jockusch Harald 
Published: September 2009

SummaryTheClc2gene of the mouse codes for the ubiquitously expressed chloride channel ClC-2, a member of a family of at least seven voltage gated chloride channels, some of which are implicated in hereditary diseases. Using a mouse interspecies back-cross panel, we have mappedClc2to Chr 16, proximal to the somatostatin geneSmst, extending a region of documented conserved synteny to human Chr 3q.
Does monozygotic twinning occur in mice?
Authors: McLaren Anne , Molland Paul , Signer Esther 
Published: September 2009

SummaryPublished reports suggest that the incidence of monozygotic twinning in women is increased after hormonally induced ovulation. Since some statistical evidence exists to indicate that monozygotic twinning may also occur in mice, we attempted to devise a mouse system in which the incidence of such twinning could be compared after spontaneous versus hormonally induced ovulation, in order to analyse the developmental basis of such an effect. We used phenotypic identity in litters segregating for ten genetic loci (not all independent) to indicate possible twin pairs. DNA fingerprinting using three human minisatellite probes was then performed blind on these pairs and on sibling controls. From a total of over 2000 mice born, 40 apparently identical pairs were identified, on which DNA finger-printing was successfully carried out on 35 pairs. All proved to be derived from different zygotes. We conclude that monozygotic twin pairs are either extremely rare in the stock of mice that we studied, or have such reduced viability that their chance of surviving to weaning is low.
Response to selection from new mutation and effective size of partially inbred populations. II. Experiments withDrosophila melanogaster
Authors: Merchante Montserrat , Caballero Armando , López-Fanjul Carlos 
Published: September 2009

SummaryDivergent artificial selection for abdominal bristle number inDrosophila melanogasterhas been carried out starting from a genetically homogeneous base population. Lines with two different systems of mating, random (Plines) or between full sibs whenever possible (about 50%), random otherwise (Ilines) were compared. Responses after 40 generations of selection were mostly due to one or two mutations of large effect (0·2 to 2 phenotypic standard deviations) per line. Ten mutations affecting the selected trait were individually studied (five lethal and five non-lethal, these being predominantly additive). These mutations satisfactorily explain the response attained, although some minor mutations may also be involved. No evidence of epistasis for bristle number was found. The average final divergence was 57% larger in thePlines, but it was mostly due to lethals or highly deleterious mutations. Thus, after relaxation of selection, the ranking reversed and the mean divergence became significantly larger in theIlines (14%). Analysis of inbreeding showed that the very small amount of variation created by spontaneous mutations (a heritability for the selected trait of about 3%) was responsible for a reduction in the effective size of about 50% in theIlines (relative to the case with random selection), but only about 10% in thePlines. Mutational heritabilities estimated from the response to selection (0·05–0·18%) were within the range usually found for this trait in previous experiments. REML estimates account for correlations between relatives, and were much larger in those lines where the response was due to lethal mutations, as these do not contribute to response after reaching maximum frequency.
Using marker-maps in marker-assisted selection
Authors: Whittaker J. C. , Curnow R. N. , Haley C. S. , Thompson R. 
Published: September 2009

SummaryA method of using information on the location of markers to improve the efficiency of markerassisted selection (MAS) in a population produced by a cross between two inbred lines is developed. The method is closer to mapping QTL than the selection index approaches to MAS described by previous authors. We use computer simulations to compare our method with phenotypic selection and two selection index approaches, simulations being performed on three genetic maps. The simulations show that whilst MAS can be considerably more efficient than phenotypic selection differences between the three MAS methods are slight. Which of the MAS methods is best depends on a number of factors: in particular the genetic map, the time scale under consideration and the population size are of importance.
Recombination frequency and wild-type ancestry in linkage group I ofNeurospora crassa
Authors: Lavigne Stella , Frost L. C. 
Published: September 2009

A selection of single and double mutant strains was backcrossed repetitively at least four times to each of the wild-types Abbott 4A, Abbott 12aand Lindegren 1A, and then re-isolated. Twelve crisp progeny isolated from the fifth backcross to Abbott 4Awere heterogeneous for recombination frequency in the interval betweencrandme-6while thirteen crisp progeny from the fifth backcross to Lindegren 1Awere homogeneous for recombination frequency in this interval. Thirteen crisp strains from the fifth backcross to Abbott 12awere homogeneous for recombination frequency betweencrandnic-1loci. However, mutant strains which had been backcrossed independently to Lindegren 1Awere heterogeneous for recombination frequency in the intervalscr-aurandaur-nic-1.In general, recombination frequencies in crosses between strains of the same wild-type ancestry including Abbott 4 and Abbott 12 were significantly higher than those in crosses of Lindegren × Abbott 4 or Lindegren × Abbott 12 ancestry but exceptions were found. Recombination frequencies between the same markers usually, but not always, increased on inbreeding and the changes in frequency were non-uniform in the marked region in some crosses.The limitations of backcrossing as a means of transferring a mutant marker into a wild-type genome were discussed. It was concluded that inducing marker mutations anew in a given wild strain, preferably Lindegren 1A, might be more successful in obtaining constancy of map distance.
Elements of theS-gene complex
Authors: Pandey Kamla Kant 
Published: September 2009

Cultivated plants ofNicotiana alataare self-incompatible and are of two kinds: normal (N); and exceptional (M). N plants are reciprocally compatible withN.langsdorffii; M plants are compatible only as males. M plants contain an unusual allele,SFI, which has a dual action in the style: it rejects both self-pollen, andSfpollen fromN. langsdorffii. The overall results agree with the assumption that theSFIgene produces two kinds of specificity in the style:primaryspecificity, which is responsible for the rejection ofSfpollen; andsecondaryspecificity, which is responsible for the rejection of self-pollen as inSIalleles generally. The genetic sub-units concerned must be closely linked; there was no evidence for their dissociation in the 599 plants studied.In both compatible and incompatible pollinations,SFIpollen grows more slowly thanSIand, in addition, appears to depress the normal rate of growth ofSIpollen. In consequence, crossesSfSf×SISFI♂ yielded significantly fewer S.I. plants than the 50% expected. The two kinds of pollen grew at comparable rates, however, when F1(M × M) plants involving parents from different original sources were backcrossed toSfSf♀. Progenies then showed the expected 1:1 ratio of S.I. to S.C. plants. These results are assumed to be due to differential behaviour of theSFIallele according to its genetic background. The change in background would be from a degree of homozygosity, in plants from the same source, to a degree of heterozygosity, in crosses between plants from different sources.The high incidence of theSFIgene inN. alatais considered to be due to the advantage it confers on a self-incompatible population when it is overlapping with a related self-compatible population (having theSfgene). Plants carrying anSFIallele, by rejecting the Sfpollen, will restrict the spread of inbreeding and so be favoured by selection.The origin of theSFIandSfalleles are discussed in relation to the author's hypothesis ofS-gene structure.
The effects of X-rays on quantitative characters
Authors: Clayton G. A. , Robertson Alan 
Published: September 2009

1. The rate of production by X-rays of new genetic variation in two quantitative characters inDrosophila melanogaster(sternital and sternopleural bristles) has been investigated, using ‘plateaued’ populations which had reached the limit under artificial selection and, for sternital bristles only, populations which had been made genetically invariant by inbreeding. The genetic variation was always measured by the response of the population to selection. The X-rays dose given in any generation was always 1800 r. to adults.2. Seven plateaued lines had eight cycles of alternate irradiation and selection, each with its non-irradiated control. All the responses were small but in three lines they were significantly greater after irradiation.3. Selection was applied to three different inbred lines, genetically marked to detect contamination, after varying periods of irradiation. At the same time, the inbred lines and lines derived from them which had been mass mated in bottles were selected. The irradiated populations showed a greater response. The new genetic variance produced by the irradiation was approximately 10−5units/r. The estimate of the dose required to introduce new variation equal to that in a standard outbred population was 500,000 r.4. The effective population size was an important factor in the interpretation of some of these results on the long-term effects of radiation. By observing the variation between replicate lines in the frequency of a gene with a visible effect under these culture conditions (i.e. in a single culture bottle) the effective population size was estimated at sixty. Outbred populations kept under these conditions for many generations showed a reduction of genetic variability in agreement with this value.5. To investigate the possibility that the deleterious genes produced by irradiation would interfere with the response to artificial selection, a standard outbred population was irradiated and selected. In spite of the observed high frequency of recessive lethals produced, the response to selection was very similar to that of the standard population.
Nutritional studies with Scaleless chickens: I. The Sulphur-Containing Amino Acids
Authors: Abbott U. K. , Asmundson V. S. , Shortridge K. R. 
Published: September 2009

Young birds homozygous for the recessive gene,sc, had a significantly lower requirement than their normally feathered siblings for the sulphur-containing amino-acids, methionine and cystine. When fed a synthetic diet lacking in methionine, feathered birds showed the expected abrupt decrease in weight gain while Scaleless birds grew at a rate equivalent to feathered birds receiving the full diet. Scaleless birds receiving the full diet exceeded feathered birds in weight gain during the first part of the feeding trial but they required more food per gram of gain. Between Scaleless groups those fed the deficient diet dropped behind those on full diet in gain after 3 weeks but even after 6 weeks these did not differ in other respects. On the other hand among normal birds those receiving the deficient diet were higher in heat output and had relatively larger thyroid and adrenal glands than those receiving the full diet.Differences between the two phenotypes are accounted for by (1) the difference in nutritive requirements determined by feather growth, and (2) the resultant differences in heat loss which accounted for the increase in heat output, packed cell volume and heart, thyroid and adrenal gland size of Scaleless birds.The use of mutants such as Scaleless in studies concerned with requirements for specific physiological or growth purposes is suggested.