bluuebunny/crossref_metadata_2025_split huggingface dataset:
The detection of deleterious selection using ancestors inferred from a phylogenetic history
Authors: Golding G. Brain 
Published: September 2009

SummaryThe widespread use of restriction endonucleases and DNA sequencing provides a wealth of data on the genetic structure of natural populations. From such data, detailed phylogenies can be constructed and qualitatively different kinds of mutational and substitutional processes can be studied. A neutral model can be constructed to describe the frequencies of sequence haplotypes according to the haplotypes from which they arose and the types of substitution that distinguish them. One feature of such a model is that it examines the ancestors of various sequences. Deleterious selection against a character has a distinct effect on descendant sequences. Individuals containing many deleterious characters leave few or no descendants because these individuals are quickly eliminated by selection. Hence, such a model lends itself to the study of deleterious selection. It is possible to determine if selection is required by searching for any set of mutation rates that can explain an observed set of data. Simulations of artificial populations without selection suggest that this method seldom indicates selection when none is present. Furthermore, recent recombination events between the sequences do not induce false indications of deleterious selection. The method may, however, require relatively large simple sizes in order to accurately reflect the true nature of populations. The method is often very conservative and may not indicate selection when it is, in fact, present.
Changes in genetic parameters under restricted index selection
Authors: Mortimer Suzanne I. , James J. W. 
Published: September 2009

SummaryThe ability of restricted selection indices to prevent genetic change in a restricted trait over several generations of selection was studied using deterministic computer models. Four loci, two affecting each trait independently, and two pleiotropic loci, one affecting each trait in the same direction, and one with opposite effects, were modelled. In general, continued effectiveness of the restriction was achieved only when the restricted trait was affected by only one locus. In some conditions (equal gene frequencies), an independent locus and one pleiotropic locus affecting the restricted trait allowed maintenance of the restriction. The results suggest that long-term restriction may be very difficult without re-estimation of parameters.
Inheritance of a meiosis I error expressed in mouse oocytes and modulated by a maternal factor
Authors: Beermann Friedrich , Jenderny Jutta , Hummler Edith , Hansmann Ingo 
Published: September 2009

SummaryNMRI/Han mice ovulate significant numbers of diploid oocytes after gonadotrophin stimulation, most of them arrested at metaphase I. In contrast, females from other mouse strains ovulate only oocytes having completed meiosis I. We investigated the heritability of the trait Dipl I by analysing F1hybrid females from crosses between the sensitive NMRI/Han stock and two mouse strains (C3H/HeHan and BALB/c) considered as non-sensitive, and females from backcrosses to NMRI/Han males (only crosses with C3H/HeHan). The results show (1) that the trait Dipl I is inheritable; (2) that an X-chromosomal (location proximally from the X–Y pairing region) or autosomal recessive mode of inheritance is excluded; and (3) that the expression of the trait, measured as frequency of diploidy, is modulated by a maternally transmitted factor.
The accumulation of P-elements on the tip of theXchromosome in populations ofDrosophila melanogaster
Authors: Ajioka James W. , Eanes Walter F. 
Published: September 2009

SummaryLittle information exists about the mechanisms that determine the fate of mobile elements in natural populations. In this study we catalogue the distribution of 638 P-elements across 114Xchromosomes in samples drawn from three natural populations ofDrosophila melanogaster. There is an extremely high occurrence of elements at the tip relative to the rest of the euchromatic chromosome. We demonstrate that the distribution ofde novoinsertions of the P-element on a specific laboratory chromosome is markedly different; no P-elements were recovered at the tip in the 243 insertion events recorded. In contrast, insertion data for the π2chromosome suggests an elevated rate associated with the tip site although it does not appear sufficient to explain the large differential accumulation on wild chromosomes. This raises the issue of inter chromosome (or tip) variation in relative rates, as well as the possibility that rates of elimination are lower at the tip.
Genic differentiation and origin of Robertsonian populations of the house mouse (Mus musculus domesticusRutty)
Authors: Britton-Davidian Janice , Nadeau Joseph H. , Croset Henri , Thaler Louis 
Published: September 2009

SummaryThis paper examines the relation between chromosomal and nuclear-gene divergence in 28 wild populations of the house mouse semi-species,Mus musculus domesticus, in Western Europe and North Africa. Besides describing the karyotypes of 15 of these populations and comparing them to those of 13 populations for which such information was already known, it reports the results of an electrophoretic survey of proteins encoded by 34 nuclear loci in all 28 populations. Karyotypic variation in this taxon involves only centric (or Robertsonian) fusions which often differ in arm combination and number between chromosomal races. The electrophoretic analysis showed that the amount of genic variation within Robertsonian (Rb) populations was similar to that for all-acrocentric populations, i.e. bearing the standard karyotype. Moreover, divergence between the two types of populations was extremely low. These results imply that centric fusions in mice have not modified either the level or the nature of genic variability. The genetic similarity between Rb and all-acrocentric populations is not attributed to the persistence of gene flow, since multiple fusions cause marked reproductive isolation. Rather, we attribute this extreme similarity to the very recent origin of chromosomal races in Europe. Furthermore, genic diversity measures suggest that geographically separated Rb populations havein situand independent origins. Thus, Rb translocations are probably not unique events, but originated repeatedly. Two models are presented to explain how the rapid fixation of a series of chromosomal rearrangements can occur in a population without lowering variability in the nuclear genes. The first model assumes that chromosomal mutation rates are between 10−3and 10−4and that populations underwent a series of transient bottlenecks in which the effective population size did not fall below 35. In the second model, genic variability is restored following severe bottlenecks, through gene flow and recombination.
Correlation between genetic distances based on single loci and on skeletal morphology in inbred mice
Authors: Festing Michael F. W. , Roderick Thomas H. 
Published: September 2009

SummaryGenetic and morphometric distances between 12 inbred strains of mice ranging from closely related substrains to a sub-species were estimated using published data on single locus polymorphisms, and on the basis of up to 44 measurements on seven different bones, respectively. Simulation was also used to investigate sampling effects for the single loci. There were strong and statistically highly significant correlations among all measures of genetic distance ranging from 0·58 for the comparison of single loci with the logarithm of the Mahalanobis distance based on 24 measurements on four bones, to 0·72 for estimates of genetic distance based on single loci and the morphology of the mandible. These findings are in sharp contrast with those of Wayne & O'Brien (1986) who claimed that ‘structural gene and morphometric variation of mandible traits are uncoupled between mouse strains’. Their failure to find such a correlation is probably because their sample of inbred strains included only a single pair of closely related substrains, and no substrains separated for less than 40 years, and because they failed to correct for non-linearity between morphometric and single-locus measurement scales. Simulations and regression analysis suggested that genetic distances could be estimated with approximately equal precision using morphological data on bone measurements or about 10 cladistically informative single loci, which would usually involve sampling about 50 loci. Data based on single-gene markers is usually more informative than morphometric data for studying the similarity of independently-derived strains. However, similarities among closely related populations such as sublines of an inbred strain can usually be studied more efficiently using morphometry.
Effects of identity disequilibrium and linkage on quantitative variation in finite populations
Authors: Tachida Hidenori , Cockerham C. Clark 
Published: September 2009

SummaryIdentity disequilibrium, ID, is the difference between joint identity by descent and the product of the separate probabilities of identity by descent for two loci. The effects of ID on the additive by additive (a * a) epistatic variance and joint dominance component between populations and in the additive, dominance and a * a variance within populations, including the effects on covariances of relatives within populations, were studied for finite monoecious populations. The effects are formulated in terms of three additive partitions, ηb, ηa and ηd of the total ID, each of which increases from zero to a maximum at some generation dependent upon linkage and population size and decreases thereafter. ηd is about four times the magnitude of the other two but none is of any consequence except for tight linkage and very small populations. For single-generation bottleneck populations only d is not zero. With random mating of expanded populations ηb remains constant and ηa and ηd go to zero at a rate dependent upon linkage, very fast with free recombination. The contributions of joint dominance to the genetic components of variance within and between populations are entirely a function of the η's while those of a * a variance to the components are functions mainly of the coancestry coefficient and only modified by the η's. The contributions of both to the covariances of half-sibs, full-sibs and parent-offspring follow the pattern expected from their contributions to the genetic components of variance within populations except for minor terms which most likely are of little importance.
The influence of the Robertsonian translocation Rb(X.2)2Ad on anaphase I non-disjunction in male laboratory mice
Authors: Adler I.-D. , Johannisson R. , Winking H. 
Published: September 2009

SummaryA Robertsonian translocation in the mouse between theXchromosome and chromosome 2 is described. The male and female carriers of the Rb(X.2)2Ad were fertile. A homozygous/hemizygous line was maintained. The influence of theX-autosomal Robertsonian translocation on anaphase I non-disjunction in male mice was studied by chromosome counts in cells at metaphase II of meoisis and by assessment of aneuploid progeny. The results conclusively show that the inclusion of Rb2Ad in the male genome induces non-disjunction at the first meoitic division. In second metaphase cells the frequency of sex-chromosomal aneuploidy was 10·8%, and secondary spermatocytes containing two or no sex chromosome were equally frequent. The Rb2Ad males sired 3·9% sex-chromosome aneuploid progeny. The difference in aneuploidy frequencies in the germ cells and among the progeny suggests that the viability of XO and XXY individuals is reduced. The pairing configurations of chromosomes 2, Rb2Ad andYwere studied during meiotic prophase by light and electron microscopy. Trivalent pairing was seen in all well spread nuclei. Complete pairing of the acrocentric autosome 2 with the corresponding segment of the Rb2Ad chromosome was only seen in 3·2% of the cells analysed in the electron microscope. The pairing between theXand theYchromosome in the Rb2Ad males corresponded to that in males with normal karyotype. Reasons for sex-chromosomal non-disjunction despite the normal pairing pattern between the sex chromosomes may be seen in the terminal chiasma location coupled with the asynchronous separation of the sex chromosomes and the autosomes. The Rb2Ad chromosome can be useful for studies ofXinactivation, as a marker for parental derivation of theXchromosome and for mapping loci byin situhybridization.
Genetic studies on nucleolus organizer regions (NORs) in cattle
Authors: Mayr B. , Gruber K. , Brem G. , Mayrhofer G. 
Published: September 2009

SummaryExperimentally produced monozygotic twins, natural opposite sex blood chimeras (freemartins), and several pedigrees were used to evaluate the genetic influences on the nucleolus organizer region (NOR) patterns in cattle. In monozygotic twins, the NOR patterns of both twins are extremely similar. In chimeras, NOR patterns of genetically identical, peripheral blood lymphocytes (PBL) from the two partners resemble each other. In contrast, genetically different PBL (sib organ) differ significantly in the same environment. A high heritability of the individual NOR patterns is also demonstrated in our 23 pedigrees. In conclusion, our data demonstrate that variation in NOR expression is predominantly due to genetic factors.
Analysis of lines of mice selected for fat content. 1. Correlated responses in the activities of NADPH-generating enzymes.
Authors: Asante Emmanuel A. , Hill William G. , Bulfield Grahame 
Published: September 2009

SummaryEstimates of the activities (Vmax) of four enzymes that generate the coenzyme NADPH, an absolute requirement for tissue fatty-acid synthesis, and of the concentration of NADP plus NADPH were made in lines of mice differing in fat content. These lines had been selected from the same base population for 20 generations, and 3 high, 3 low replicates and 1 unselected control were used. Analyses were performed on liver and gonadal fat pad (GFP) of males at 5 and 10 weeks of age. In both the liver and the GFP, measurable activities of the four enzymes: glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), isocitrate dehydrogenase (IDH) and malic enzyme (ME) expressed per mg soluble protein were, with minor exceptions, higher in the Fat (F) than in the Lean (L) lines at both ages; the highest ratio being 2–2 for ME in the GFP. The relationships between these measurable activities (Vmax) andin vivolipogenesis are not however known. When expressed per gram tissue, the ratios for F to L in the GFP were less than 1 in most cases, presumably because of the very different adipocyte numbers and/or sizes between the lines. There were no significant differences between the lines in the concentration of NADP plus NADPH per gram tissue in liver or GFP, suggesting that F lines converted NADP to NADPH faster than L lines. It is predicted that selection on the enzyme activities would be less efficient than direct selection at changing fat content.
Reconstruction of allopolyploid Brassicas through non-homologous recombination: introgression of resistance to pod shatter inBrassica napus
Authors: Prakash Shyam , Chopra V. L. 
Published: September 2009

SummaryPod shattering of rapeseed (Brassica napus) causes serious yield loss. Genetic resistance to shattering has been introgressed intoB. napusfromB. juncea. This followed from allosyndetic pairing between chromosomes of B and C genomes in the interspecific F1 hybrid,B. juncea×B. napus(2n= 37, AABC). The reconstitutedB. napusplant showed regular meiosis with 19 bivalents and had pollen and seed fertility of 84 and 23% respectively. An approach is suggested for achieving introgression from monogenomic diploids to digenomic allopolyploids that exploits non-homologous recombination.
Are responses to artificial selection for reproductive fitness characters consistently asymmetrical?
Authors: Frankham R. 
Published: September 2009

SummaryNon-linear offspring-parent regressions and heritabilities are expected for characters showing genetic asymmetry due to directional dominance and/or asymmetrical gene frequencies. Since reproductive fitness characters exhibit these characteristics, they should show consistently nonlinear heritabilities, with greater heritabilities in the direction of lower fitness. As a consequence, responses to bi-directional selection on fitness traits should be asymmetrical in the same direction. This prediction has been tested by an analysis of published bi-directional selection experiments for reproductive fitness traits. Significant asymmetry (24 of 30 studies) in the predicted direction was found. For studies reporting realized heritabilities, the means were 0·173 and 0·259 for lines selected for higher and lower reproductive fitness, respectively, the high lines being 33% less than the low lines. Asymmetry was evident for studies reporting realized heritabilities and for those with random mating controls of the same size as the selection lines. Consequently, it is argued that the asymmetry results from genetic asymmetries. This asymmetry has important implications in the improvement of reproductive fitness traits in plant and animal breeding.
Time-dependent changes in gene conversion inAscobolus immersus
Authors: Helmi Shacker , Lamb Bernard C. 
Published: September 2009

SummaryThe stability of conversion frequencies with time was investigated inAscobolus immersus. There were usually marked reductions in gene conversion frequencies at locuswlas crosses matured, to about one third of the initial values. This applied to all sixwlalleles tested, irrespective of their molecular nature, and at all temperatures used. Asci dehiscing early from an apothecium had much higher conversion frequencies than those dehiscing late, but there were no differences between apothecia maturing at different times within a cross. Alleles at four loci unlinked towlwere also tested. All four showed significant changes, though not in all crosses; three loci showed decreases in conversion frequency with time, while one showed an increase. The relative frequencies of different conversion classes often changed with time. These changes appear to result from alterations in locus-specific recombination initiation and in repair of base mispairs in hybrid DNA, not from differential maturation rates of different ascal segregation classes. These effects could cause misinterpretation of quantitative tests of recombination models from gene conversion data.
A mutation resulting in increased triosephosphate isomerase activity inMus musculus
Authors: Merkle Siegbert , Reitmeir Peter , Pretsch Walter 
Published: September 2009

SummaryA mutation resulting in increased triosephosphate isomerase (TPI) activity in blood was recovered in offspring of procarbazine hydrochloride-treated male mice. Breeding experiments indicated a codominant mode of expression. Compared to the wild type, heterozygous and homozygous mutants have mean erythrocyte TPI activities of approximately 140 and 190%, respectively. Besides blood and erythrocytes the increased activity is expressed to a similar degree in spleen, and to a lesser degree in liver, lung, kidney, muscle and brain. Enhanced activity was absent in the heart. Heterozygous and homozygous mutants are viable, fully fertile and exhibit no significant differences in haematological or other physiological traits studied. Biochemical investigations of TPI in both mutant genotypes revealed neither physicochemical nor kinetic differences compared to the wild type. Moreover, immunoinactivation studies showed no difference in the amount of antiplasma required to inactivate a constant amount of TPI activity in all three genotypes, strongly suggesting that the differences in enzyme activity are attributable to differing amounts of enzyme protein expressed per cell. Mapping studies indicated that the mutation is closely linked to theGapdlocus and consequently is located either adjacent to or within theTpi-1structural locus. It is hypothesized that the mutation affected a regulatory element contiguous to theTpi-1structural locus which acts by increasing the amount of TPI expressed.
Nucleolus organizer-suppressed position-effect variegation inDrosophila melanogaster
Authors: Spofford Janice B. , DeSalle Rob 
Published: September 2009

SummaryThewhitelocus is inactivated in a cell-by-cell variegated pattern when juxtaposed with the proximal or distal parts of the nucleolus organizer region (NO) by X chromosome inversion. Recombinants for two such inversions,wm51bandwm4, were obtained and randomized for genetic background.Whitelocus activity was much higher in thewm4recombinant duplicated for most of theNOand much lower in thewm51brecombinant deficient for it. Although there may be other molecular differences between the heterochromatic regions of the recombinants, the most obvious is the dosage ofNO.Suppression of aNOregion-evoked variegated phenotype by additionalNOdoses is discussed in relation to four different classes of models for position-effect variegation (PEV): chromatin structure, nuclear geometry, incomplete transposition of mobile elements, and heterochromatin promoter-driven transcription. A corollary of the structural model is functional subdivision of heterochromatin, which would enable the use of PEV as a tool for its study.
Population genetics of the Y chromosome ofDrosophila melanogaster: rDNA variation and phenotypic correlates
Authors: Clark Andrew G. , Szumski Frances M. , Lyckegaard Eva M. S. 
Published: September 2009

SummaryOne means of examining the evolutionary significance of molecular variation on the Y chromosome is to identify phenotypes specifically affected by Y-linked genes, and to quantify the phenotypic variation and its correlation to the molecular variation. The functional importance of the Y-linked array of rRNA genes is demonstrated by the ability of Y chromosome to rescue X-linkedbobbedlethal alleles, whose lethality is seen in homozygous females. Because low numbers of X-linked rDNA gene copies result in increased developmental time and shortened bristles, and because there is considerable natural variation in Y-linked copy number, a careful examination of Y-linked variation in these two traits may uncover a mode of selection acting on the multigene family. In this study, 36 Y-chromosome replacement lines were tested to detect subtle variation in bristle phenotypes and developmental rates. Correlations among these traits, rDNA gene copy number, and intergenic sequence length were quantified. The absence of significant correlations between phenotypic characters and rDNA copy number or intergenic sequence length suggests that the extant molecular variation in Y-linked rDNA can have at most very small selective effects.