bluuebunny/crossref_metadata_2025_split huggingface dataset:
The constraints of finite size in asexual populations and the rate of the ratchet
Authors: Gessler Damian D. G. 
Published: September 2009

SummaryAn analysis of mutation accumulation in finite, asexual populations shows that by modeling discrete individuals, a necessary condition for mutation–selection balance is often not met. It is found that over a wide parameter range (wheneverN e−μ/s< 1, whereNis the population size, μ is the genome-wide mutation rate, andsis the realized strength of selection), asexual populations will fail to achieve mutation–selection balance. This is specifically because the steady-state strength of selection on the best individuals is too weak to counter mutation pressure. The discrete nature of individuals means that if the equilibrium level of mutation and selection is such that less than one individual is expected in a class, then equilibration towards this level acts to remove the class. When applied to the classes with the fewest mutations, this drives mutation accumulation. This drive is in addition to the well-known identification of the stochastic loss of the best class as a mechanism for Muller's ratchet. Quantification of this process explains why the distribution of the number of mutations per individual can be markedly hypodispersed compared to the Poisson expectation. The actual distribution, when corrected for stochasticity between the best class and the mean, is akin to a shifted negative binomial. The parameterization of the distribution allows for an approximation for the rate of Muller's ratchet whenN e−μ/s< 1. The analysis is extended to the case of variable selection coefficients where incoming mutations assume a distribution of deleterious effects. Under this condition, asexual populations accumulate mutations faster, yet may be able to survive longer, than previously estimated.
Effect of non-random sampling on the estimation of parameters in population genetics
Authors: Tajima Fumio 
Published: September 2009

SummaryThe amount and pattern of genetic variation in a population can be estimated from genes or DNA sequences sampled from the population. Although random sampling is assumed in almost all cases, we often do not know whether sampling is random or not. Using a simple non-random sampling model, the effects of non-random sampling on the estimation of parameters in population genetics were investigated. This non-random sampling model assumes thatngenes are randomly sampled with replacement frommgenes which were randomly sampled from a large random mating population, and various degrees of non-randomness can be generated by changing the value ofm. The results obtained show that the effect of non-random sampling on the number of alleles and the number of segregating sites is substantially large whereas the effect of non-random sampling on heterozygosity and the average number of nucleotide differences is negligibly small unless non-randomness is extremely large. The effects of non-random sampling on the tests of neutrality were also investigated, and the results obtained indicate that the effect of non-random sampling is stronger on Fu and Li's tests than on Tajima's test.
Genetic variation of relative growth rates inNotonecta undulata: I. The relation of femur length to body length
Authors: Misra R. K. , Reeve E. C. R. 
Published: September 2009

This paper presents the first part of a further analysis of data collected many years ago by Clark and Hersh on allometric growth inNotonecta undulata, the water boatman. The data consist of measurements of a number of dimensions, taken each instar, on 72 individuals reared separately from egg to adult. These individuals were the progeny of nine wild females, so that a rough estimate can be made of the magnitude of genetic effects by comparing the variances within and between families. The paper examines the allometric relationship between femur length of the three legs and body length.The statistical problems in this type of analysis are discussed. There are significant deviations from linearity when the six points for femur length are plotted against body length on a double log graph, but these are small compared with the overall linear trend. The growth coefficients (k) are calculated for the three femurs against body length for each individual, and are analysed for differences between femurs, between sexes and between and within families. This analysis shows that there are significant differences between the three femurs in growth coefficient, but the growth gradient, or pattern ofkvalues between the three femurs does not vary significantly from one individual to another. On the other hand, meankfor the three femurs shows significant individual variation and also a significant variation between families. From this it appears that about one third of the phenotypic variance in mean relative growth rate of the femurs is due to genetic effects.
The pattern of mutation of an unstable gene in Delphinium ajacis
Authors: Dawson G. W. P. 
Published: September 2009

1. Inheritance of flower colour in Delphinium ajacis is controlled by a locus with three stable alleles: pb (blue) is dominant to pl (lavender), which is dominant to p (pink). An unstable allele, p*, exists in a number of states, distinguished by the pattern of their mutation to pb and p during the development of the sepals.2. The rate of occurrence of blue sectors and spots in the developing sepals of p*p* plants is twice that in the sepals of p*pl plants. The rate of mutation to pb apparently falls during the development of the sepals and this is probably due to p* mutating also to the stable p allele.3. The frequency of pb and p gametes from p*p* plants is twice that from p*pl plants.4. The pb mutants from p* show no evidence of instability; the controlling element has transposed from the locus.5. Some p mutants from p* are apparently stable; others can reacquire instability, especially during sexual reproduction. The latter are tentatively interpreted as due to transpositions of the controlling element to other sites within the gene.6. The instability of p* is only shown in the presence of a dominant activator.7. Evidence is presented of transposition of the controlling element from p* to a locus controlling the colour of the foliage.
Mi-spotted: a mutation in the mouse
Authors: Wolfe H. Glenn , Coleman D. L. 
Published: September 2009

Mi-spotted (misp) is a new mutation in the mouse at the microphthalmia (mi) locus. It has no obvious visible effect in either the heterozygote (misp/+) or homozygote (misp/misp) and was discovered by virtue of its interaction with white (miwh). Mice of genotypemiwh/mispare pale yellow with white spots; yellow areas later become ‘sooty’ at the first moult.Though mice of genotypesa/a;misp/+ anda/a;misp/mispcannot be visibly distinguished from those ofa/a; +/+, the amount of tyrosine-2-C14incorporated in melanin in skins of 5-day-old mice of these genotypes differed. Assays of tyrosine incorporation were extended to include other non-agouti genotypes differing only at the microphthalmia locus. The amount of tyrosine incorporated was greatest in +/+ followed in order bymisp/+,misp/+,misp/misp,miwh/+,miwh/misp, andmiwh/miwh.Pigment granules were examined in club hairs of these same genotypes for different regions of the hair shaft. Hairs ofmisp/+,misp/misp, andmi/+ could not be distinguished from +/+ either in number, kind or arrangement of granules. Hairs ofmiwh/+ showed reduced cortical and medullary pigment, especially distally, which was even more pronounced in hairs ofmiwh/misp. Medullary granules ofmiwh/mispvaried greatly in size with a few large yellow-brown granules.
Cytological observations on a duck hybrid: Anas clypeata × Anas penelope
Authors: Slizynski B. M. 
Published: September 2009

The chromosomes of the two parental forms and those of the hybrid do not show any detectable numerical or large structural differences. The pairing in the hybrid is frequently abnormal in that both free ends (highly charged with stainable substances) of many chromosomes show strong pairing, while midsegments repel each other. This partial failure of paring suggests that in the two parental forms gene mutations rather than chromosomal structural changes are responsible for incipient divergence.It is suggested that the stainable substance of the chromosomes acts as a carrier mechanism ensuring orderly pairing, segregation and numerical constancy of bivalents in the hybrid where the partner chromosomes have become partly non-homologous.The distinction between long and short chromosomes is typical for the avian karyotype, its evolutionary significance is discussed.
The effect of dose-rate on the yield of translocations and dominant lethals following spermatogonial irradiation of mice
Authors: Phillips R. J. S. , Searle A. G. 
Published: September 2009

1. F1 (CSH♀ × 101♂) male mice were given 1200 r. 60Co Υ-irradiation over welve weeks and mated twelve weeks after the end of irradiation. The incidences of foetal and neonatal lethality and of semi-sterility in their offspring were compared with those in controls.2. Embryonic survival to 15 days in the irradiated series was 98·2% that of controls, while the incidence of semi-sterility was 0·9% compared with nil in the controls. Neither of these differences is significant.3. Comparison of these results with the significant rates of induction of dominant lethals and translocations in a previous experiment, in which a dose of 1200 r. acute x-irradiation was given to males of the same hybrid stock, show the existence of a dose-rate effect. Its magnitude cannot at present be accurately estimated.4. The reasons for this effect are discussed. It is concluded that the main cause of the lowered translocation yield is that restitution of breaks will be favoured at low dose-rates, with less opportunity for the formation of interchanges. This could partly account for the lowered rate of induction of dominant lethals as well, but a full explanation is not yet possible.
Diabetes insipidus associated with oligosyndactyly in the mouse
Authors: Falconer D. S. , Latsyzewski M. , Isaacson J. H. 
Published: September 2009

1. A mild diabetes insipidus is associated with the oligosyndactyly caused by the dominant gene Os. No recombinants were observed between the diabetes and the oligosyndactyly so the diabetes is probably a pleiotropic effect of the Os gene.2. There are one or more modifying genes which in combination with Os enhance the manifestation and cause a severe diabetes insipidus. This affects both sexes and becomes progressively worse in older animals, the average water intake reaching 50–60 ml. per 24 hours, or 1·7 times the body weight.3. The modifying gene or genes, in the absence of the Os gene, themselves produce a mild diabetes insipidus, which becomes severe in some old females.4. The severe diabetes insipidus associated with Os and the modifying genes together is probably renal in origin.
Changing the relative size of the body parts ofDrosophilaby selection
Authors: Robertson Forbes W. 
Published: September 2009

1. Mass selection for both high- and low-ratio of wing to thorax length has been carried out on a population ofDrosophila melanogaster. The response to selection was immediate and sustained. When the experiment was stopped after ten generations, the wing area in the two selected lines differed by about 30%. The heritability estimate worked out at 0·56 ± 0·08.2. Thorax length remained comparatively unchanged during selection nor was there any change in wing shape. There was some evidence of assymetry of response since there was a relatively greater change in favour of smaller rather than larger size.3. The tibia length of all pairs of legs showed correlated changes so that the lines with larger or smaller wing sizes had also larger and smaller legs.4. The normal allometric relation between wing and thorax length, associated with variation in body-size, apparently also changed, so that for a given change in thorax length there was a greater or smaller proportional change in wing size in the high- or low-ratio lines.5. The changes in relative wing size are due to changes in cell number.6. It is suggested that the genetic changes due to selection act in the early pupal period when the imaginal discs are undergoing differentiation and proliferation to form imaginal hypoderm and appendages.7. Tests of genetic behaviour failed to show any departure from additivity in crosses which involved the unselected population and the high-ratio line. But highly significant departures existed in the cross to the low-ratio line. Relatively smaller wing size behaves as largely recessive. Stability of the normal wing/thorax ratio involves dominance and probably also epistasis. The genetic properties of the relative size of the appendage are apparently similar to those which characterize body-size as a whole.8. It is suggested that selection provides a valuable tool for studying the constancy or lability of the growth patterns which determine morphology.
Transfer delay and chromosome withdrawal during conjugation inEscherichia coli
Authors: De Haan P. G. , Gross J. D. 
Published: September 2009

Chromosome transfer has been studied in mating pairs formed during a 5-minute interval, under conditions that prevent the formation of new pairs. It has been found that, despite restriction of the period of effective contact formation, there is a considerable spread in the time at which transfer is initiated in the different mating pairs. In some pairs there is a delay of as much as 15 minutes before transfer commences.The presence of broth in the medium in which transfer takes place leads to a marked reduction in the stability of pairs involving some Hfr strains, but has little or no effect on pairs involving others. The action of broth can be ascribed to the effect of a complete mixture of amino-acids on the metabolic activity of the donor cells.A segment of chromosome which has penetrated from the Hfr into the F−cell may be subsequently withdrawn. Withdrawal may take place in more than half of the mating pairs, and probably occurs at the time when the donor and recipient cells separate. It is prevented if the chromosome breaks when conjugation is interrupted.
The kinetics of chromosome transfer in Escherichia coli: a mathematical treatment
Authors: Symonds N. 
Published: September 2009

A mathematical treatment has been presented of the ideas of de Haan & Gross concerning transfer delay and chromosomal withdrawal during conjugation In Escherichia coli. The calculations involve three parameters: (i) the maximum delay, λ, which can occur between the formation of effective contact in mating pairs and the initiation of chromosomal transfer, (ii) the probability, b, that mating pairs separate with the withdrawal of that segment of the Hfr chromosome which has entered the female cell, and (iii) the probability, c, that mating pairs separate with the breakage of the Hfr chromosome at the point where it enters the female cell, leaving the injected fragment in the female.A comparison of the theory with the experimental results of de Haan & Gross obtained when chromosomal transfer occurs either in minimal medium or in broth shows good agreement under the following conditions:(i) the value of λ is the same under both growth conditions,(ii) the value of b is the same under both growth conditions,(iii) the value of c is much greater during transfer in broth than it is in minimal medium.
Insights into X chromosome inactivation from studies of species variation, DNA methylation and replication, and vice versa
Authors: Migeon Barbara R. 
Published: September 2009

SummaryI am indebted to Mary Lyon as her X-inactivation hypothesis stimulated my mentor, Barton Childs, and in turn, myself, to think about the consequences of X-inactivation in heterozygous females. I often reread her original papers setting forth the single active X hypothesis, and still marvel at the concise and compelling exposition of the hypothesis and the logical predictions which seemed prophetic at my first reading, and have survived the test of time.My contribution to this Festschrift reviews evidence derived from studies of DNA methylation, species variation and DNA replication that reveals an important role for methylated CpG islands and suggests a role for late DNA replication in propagating X inactivation from one cell to its progeny. These studies also show that X inactivation is a powerful research tool for identifying the factors which program and maintain developmental processes.
The search for the mouse X-chromosome inactivation centre
Authors: Rastan S. , Brown S. D. M. 
Published: September 2009

SummaryThe phenomenon of X-chromosome inactivation in female mammals, whereby one of the two X chromosome present in each cell of the female embryo is inactivated early in development, was first described by Mary Lyon in 1961. Nearly 30 years later, the mechanism of X-chromosome inactivation remains unknown. Strong evidence has accumulated over the years, however, for the involvement of a major switch or inactivation centre on the mouse X chromosome. Identification of the inactivation centre at the molecular level would be an important step in understanding the mechanism of X-inactivation. In this paper we review the evidence for the existence and location of the X-inactivation centre on the mouse X-chromosome, present data on the molecular genetic mapping of this region, and describe ongoing strategies we are using to attempt to identify the inactivation centre at the molecular level.
Illegitimate pairing of the X and Y chromosomes in Sxr mice
Authors: Cattanach B. M. , Rasberry C. , Burtenshaw M. D. , Evans E. P. 
Published: September 2009

SummaryX/Y male mice carrying the sex reversal factor, Sxr, on their Y chromosomes typically produce 4 classes of progeny (recombinant X/X Sxr ♂♂ and X/Y non-Sxr ♂♂, and non-recombinant X/X ♀♀ and X/Y Sxr ♂♂) in equal frequencies, these deriving from obligatory crossing over between the chromatids of the X and Y during meiosis. Here we show that X/Y males that, exceptionally, carry Sxr on their X chromosome, rather than their Y, produce fewer recombinants than expected. Cytological studies confirmed that X-Y univalence is frequent (58%) at diakinesis as in X/Y Sxr males, but among those cells with X-Y bivalents only 38% showed normal X-Y pseudo-autosomal pairing. The majority of such cells (62%) instead showed an illegitimate pairing between the short arms of the Y and the Sxr region located at the distal end of the X, and this can be understood in terms of the known homology between the testis-determining region of the Y short arm and that of the Sxr region. This pairing was sufficiently tenacious to suggest that crossing over took place between the 2 regions, and misalignment and unequal exchange were suggested by indications of bivalent asymmetry. Metaphase II cells deriving from meiosis I divisions in which the normal X-Y exchange had not occurred were also found. The cytological data are therefore consistent with the breeding results and suggest that normal pseudo-autosomal pairing and crossing over is not a prerequisite for functional germ cell formation. The data support the concept that Y short arm-Sxr pairing and crossing over may be the mechanism responsible for the occurrence of the Sxr variants reported in the literature.
Sex chromosome configurations in pachytene spermatocytes of an XYY mouse
Authors: Tease Charles 
Published: September 2009

SummaryKaryotypic investigation of a phenotypically normal but sterile male mouse showed the presence of an XYY sex chromosome constitution. The synaptic behaviour of the three sex chromosomes was examined in 65 pachytene cells. The sex chromosomes formed a variety of synaptic configurations: an XYY trivalent (40%); an XY bivalent and Y univalent (38·5%); an X univalent and YY bivalent (13·8%); or X, Y, Y univalence (7·7%). There was considerable variation in the extent of synapsis and some of the associations clearly involved nonhomologous pairing. These observations have been compared with previously published information on chromosome configurations at metaphase I from other XYY males.
Conserved loci on the X chromosome confer phosphate homeostasis in mice and humans
Authors: Scriver Charles R. , Tenenhouse Harriet S. 
Published: September 2009

SummarySeveral genes expressed in kidney and other tissues determine phosphate homeostasis in extracellular fluid. The major form of inherited hypophosphatemia in humans involves an X-linked locus (HPDR, Xp22.31-p21.3). It has two murine homologues (HypandGy) which map to closely-linked but separate loci (crossover value 0·4%–0·8%). Both murine mutations impair Na+-phosphate cotransport in renal brush border membrane; an associated renal disorder of 1, 25-dihydroxyvitamin D3(1, 25(OH)2D) metabolism has been characterized inHypmice. Whereas experiments with culturedHyprenal epithelium indicate that the gene is expressed in kidney, studies showing the development of the mutant renal phenotype in normal mice parabiosed toHypmice implicate a circulating factor; these findings can be reconciled if the humoral factor is of renal origin. The gene dose effect of HPDR,HypandGyon serum phosphorus values is consistently deviant and heterozygotes resemble affected hemizygotes. The deviant effect is also seen on renal phosphate transport; all mutant females(Hyp/HypandHyp/+) have similar phenotypes. On the other hand, there is a normal gene dose effect of HPDR in mineralized tissue; tooth PRATIO (pulp area/tooth area) values for heterozygotes are distributed between those for affected males and normals. The tooth data imply that the X chromosome locus is expressed in both renal and non-renal cells. The polypeptide product of the X chromosome gene(s) is still unknown.
Localization of the properdin factor complement locus Pfc to band A3 on the mouse X chromosome
Authors: Evans E. P. , Burtenshaw M. D. , Laval S. H. , Goundis D. , Reid K. B. M. , Boyd Y. 
Published: September 2009

SummaryThe locus for properdin (properdin factor complement, Pfc), a plasma glycoprotein, has been mapped to band A3 of the mouse X chromosome by in situ hybridization to metaphase spreads containing an X;2 Robertsonian translocation. The X-linkage of the locus has also been confirmed by analysis of Mus musculus x Mus spretus interspecific crosses. The XA3 localization for Pfc places it in the chromosomal segment conserved between man and mouse which is known to contain at least six other homologous loci (Cybb, Otc, Syn-1 Maoa, Araf, Timp).
Hst-3: an X-linked hybrid sterility gene
Authors: Guénet Jean-Louis , Nagamine Claude , Simon-Chazottes Dominique , Montagutelli Xavier , Bonhomme François 
Published: September 2009

SummaryA gene, Hst-3, responsible for sterility in F1 males from crosses between Mus spretus and laboratory strains of mice such as C57BL/6, has been localized on the distal part of the X chromosome, using both DNA probes and biochemical markers on a panel of Fl(C57BL/6 × SEG) × C57BL/6 backcross males. This gene may be a model for studying mammalian hybrid sterility.
The hairy ears (Eh) mutation is closely associated with a chromosomal rearrangement in mouse chromosome 15
Authors: Davisson Muriel T. , Roderick Thomas H. , Akeson Ellen C. , Hawes Norman L. , Sweet Hope O. 
Published: September 2009

SummaryThe mouse mutation hairy ears (Eh) originated in a neutron irradiation experiment at Oak Ridge National Laboratory. Subsequent linkage studies withEhand other loci on Chr 15 suggested that it is associated with a chromosomal rearrangement that inhibits recombination since it shows tight linkage with several loci occupying the region extending from congenital goiter (cog) distal to caracul (ca). We report here (1) linkage experiments confirming this effect on recombination and (2) meiotic and mitotic cytological studies that confirm the presence of a chromosomal rearrangement. The data are consistent with the hypothesis of a paracentric inversion in the distal half of Chr 15. The effect of the inversion extends over a minimum of 30 cM, taking into account the genetic data and the cytologically determined chromosomal involvement extending to the region of the telomere.