bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased intragenic recombination and non-disjunction in the Rec-1 strain ofCaenorhabditis elegans
Authors: Rattray B. , Rose A. M.
Published: September 2009

The Rec-1 strain ofCaenorhabditis elegansincreases recombination frequency three-fold. In this paper, we have investigated the effect of Rec-1 on the intragenic recombination phenomena of crossing-over and gene conversion. These events were increased two- to three-fold as wasX-chromosome non-disjunction. All of the recovered recombinants were independent events, indicating that Rec-1 does not act pre-meiotically. The pattern of recombination in the Rec-1 strain resembles a meiotic pattern more than a radiation expansion. We conclude from this result that the Rec-1 enhancement of recombination is not the result of an increased number of DNA lesions randomly distributed along the chromosome. The increased recombination frequency of Rec-1 was not accompanied by any detrimental effects on growth, progeny number or spontaneous mutation rate. In this regard, the results may have implications for models which propose either selective advantage or disadvantage accompanying increased recombination.
The relationship between position and expression of genes on the kangarooXchromosome suggests a tissue-specific spread of inactivation from a single control site
Authors: Graves Jennifer A. Marshall , Dawson Garey W.
Published: September 2009

In marsupials,Xchromosome inactivation is paternal and incomplete. The tissue-specific pattern of inactivation ofX-linked loci (G6PD, PGK, GLA) has been attributed to a piecemeal inactivation of different regions of theX. We here propose an alternative hypothesis, in which inactivation of the marsupialXis a chromosome-wide event, but is differentially regulated in different tissues. This hypothesis was suggested by the relationship between the positions and activity of genes on the kangaroo paternalX. In the absence of an HPRT polymorphism, we have used somatic cell hybridization to assess the activity of the paternal HPRT allele in lymphocytes and fibroblasts. The absence of the paternalX, and of the paternal forms of G6PD or PGK, from 33 cell hybrids made by fusing HPRT-deficient rodent cells with lymphocytes or fibroblasts of heterozygous females, suggests that the HPRT gene on the paternalXis inactive in both tissues and therefore not selectable. Since HPRT is located medially on theXqnear GLA, which shares the same characteristics of activity, we suggest that the locus-specific and tissue-specific patterns of activity result from a differential spread of inactivation from a single control locus, located near HPRT and GLA, outwards in both directions to G6PD and PGK. The nucleolus organizer region on the short arm does not seem to be part of the inactivated unit.
Three newt-haplotypes ofMus musculusreveal structural similarities tot-haplotypes ofMus domesticus
Authors: Forejt Jiří , Gregorová Soňa , Jansa Petr
Published: September 2009

Three newt-haplotypes,tp 4,tp 12andtp 14, were isolated fromM. musculusmale mice captured in Central and East Bohemia, Czechoslovakia, about 400 km from the zone of hybridization betweenM. musculusandM. domesticusspecies. Complementation tests have shown that all three newt-haplotypes belong totw 73group. When compared with 5t-haplotypes fromM. domesticusthey displayed the same pattern ofBamHI restriction fragments withH-2class I genes, and they also shared thet-specific 5·2 kbTaqI fragment of the alpha globin pseudogene. However, they differed fromM. domesticus t-haplotypes at the D17Leh443 locus since they all displayed a 10·5 kbMspI fragment, labelled by the Tu443 probe, not found in wild type-chromosomes or inM. domesticus t-haplotypes. A hypothesis is proposed thatt-haplotypes inM. domesticusoriginated by a single successful introgression from a parental species during speciation.
The rate of polygenic mutation
Authors: Lynch Michael
Published: September 2009

By application of the neutral model of phenotypic evolution, quantitative estimates of the rate of input of genetic variance by polygenic mutation can be extracted from divergence experiments as well as from the response of an inbred base population to selection. The analytical methods are illustrated through a survey of data on a diversity of organisms includingDrosophila, Tribolium, mice, and several crop species. The mutational rate of introduction of genetic variance (Vm) scaled by the environmental variance (VE) is shown to vary between populations, species, and characters with a range of approximately 10−4to 5 × 10−2.Vm/VEforDrosophilaviability is somewhat below this range, while hybrid dysgenesis may temporarily inflateVm/VEbeyond 10−1. Potential sources of bias and error in the estimation ofVmare discussed, as are the practical implications of the observed limits toVm/VEfor projecting the long-term response to selection and for testing adaptational hypotheses.
Clustering of rDNA containing type 1 insertion sequence in the distal nucleolus organiser ofDrosophila melanogaster: implications for the evolution of X and Y rDNA arrays
Authors: England P. R. , Stokes H. W. , Frankham R.
Published: September 2009

The ribosomal RNAs produced by the multigene families on theXandYchromosomes ofDrosophila melanogasterare very similar despite the apparent evolutionary isolation of theXandYchromosomal rDNA.X–Yexchange through the rDNA is one mechanism that may promote co-evolution of the two gene clusters by transferringYrDNA copies to theXchromosome. This hypothesis predicts that the proximal rDNA ofXchromosomes will beY-like. Consequently, rDNA variants found only on theXchromosome (such as those interrupted by type 1 insertions) should be significantly clustered in the distalXnucleolus organizer. Proximal and distal portions of theXchromosome nucleolus organizer were separated by recombination between the inverted chromosomesIn(1)scv2(breakpoint in the centre of the rDNA) andIn(1)sc4Lsc8R(no rDNA). Molecular analyses of the resulting stocks demonstrated that rRNA genes containing type 1 insertions were predominantly located on the chromosome carrying the distal portion of theXrDNA, thus confirming a prediction of theX–Yexchange hypothesis for the co-evolution ofXandYchromosomal rDNA. Distal clustering is not predicted by the alternative hypotheses of selection or gene conversion.
Specificities of IncF plasmid conjugation genes
Authors: Willetts Neil , Maule John
Published: September 2009

The conjugation regions of IncF plasmids are closely related in that they share extensive DNA homology, and that they specify related pili. Variations between individual conjugation gene products of different IncF plasmids have, however, been noted. We have extended these observations by carrying out a systematic survey of twelve such plasmids, to examine the numbers and the groupings of the plasmid-specific alleles of several genes required for conjugation and its control.

Using vector plasmids carrying cloned origins of transfer (oriT), four different specificities were recognized, and these were correlated with the specificities of the genes with products that may act at this site (traM, traYandtraZ). ThetraYgene is the first gene of the major transfer operon, and is therefore located close to the site at which thetraJprotein acts to induce expression of the operon: correspondingly, correlation was observed between theoriT/traMYZandtraJspecificities in most of the plasmids. In turn,traJis negatively regulated by thefinOandfinPproducts acting in concert: thefinOproduct was relatively non-specific, but sixfinPalleles were identified, again with specificities correlated with those oftraJ. Our explanation for this unexpectedly large number offinPalleles derives from the concept that thefinPproduct is an RNA molecule rather than a protein. Although the conjugative pili encoded by IncF plasmids are closely related, they confer different efficiencies of plating of the various F-specific bacteriophages. We distinguished four groups on this basis, presumably resulting from differences in the primary amino-acid sequences of the pilin proteins. These groups could be related to the surface exclusion system specificities, consistent with the hypothesis that surface exclusion acts at least in part by preventing interaction between the pilus and the recipient cell surface.

From these data, information about the evolutionary relationships between the twelve IncF plasmids can be deduced.
Assaying chromosome arrangement in embryonic interphase nuclei ofDrosophila melanogasterby radiation induced interchanges
Authors: Hilliker Arthur J.
Published: September 2009

Despite recent advances in our understanding of chromatin ultrastructure, little is known of the arrangement of chromosomes during interphase, the portion of the cell cycle associated with somatic gene transcription. An experimental procedure is described which has allowed the determination of the nature of the relative arrangement during interphase of chromosomes in a specific diploid cell type of Drosophila, the salivary gland anlage of the 10–14-h-old embryo. At this stage of development the salivary gland cells have ceased mitotic divisions. Embryos of 10–14 h in age were irradiated with 12000 rads of gamma radiation and then allowed to develop into third instar larvae. The polytene chromosomes of these larvae were examined for radiation-induced interchanges. From the distribution of observed interchanges, three major features of interphase chromosome arrangement were inferred. (1) Each euchromatic chromosomal arm occupies a specific domain within the interphase nucleus which does not appreciably overlap with those of other arms. (2) Within these chromosomal domains DNA folding is very extensive. (3) The heterochromatic regions of each chromosomal arm are sequestered from the euchromatic regions. An additional point of interest concerns the nature of the interchanges observed. No reciprocal interchanges were observed – all appeared to be partial exchanges, possibly subchromatid interchanges involving only one DNA strand from each of the two exchange sites.
Effects of alleles at the agouti locus on minor skeletal variants in C57BL/6 house mice
Authors: Leamy Larry , Bradley David
Published: September 2009

In this study, five separate alleles at the agouti locus in house mice were tested for potential effects on a battery of 13 minor skeletal variants. Six genotypes (aa,ata,atat,Aa,Avya, andAya) were compared on a standard congenic background (C57BL/6). In log-linear analyses, three of the 13 characters showed significant genotype differences (another three were close to significance), and genotypes also exhibited overall significance in a multivariate randomization test. Both multidimensional scaling and clustering showed an association ofaawithata,AawithAvyaandAya, and a general separation ofatatfrom the other genotypes. Genotype differences averaged 0·63 in probit standard deviations, 0·09 when assessed by the mean measure of divergence. Since the general magnitude of effects of these major genes was quite similar to those previously estimated for presumptive polygenes from subline divergence studies, it was concluded that major genes may often act as polygenes and make important contributions to the variation in minor skeletal variants.
Fitness as a function of β-galactosidase activity inEscherichia coli
Authors: Dean Antony M. , Dykhuizen Daniel E. , Hartl Daniel L.
Published: September 2009

Chemostat cultures in which the limiting nutrient was lactose have been used to study the relative growth rate ofEscherichia coliin relation to the enzyme activity of β-galactosidase. A novel genetic procedure was employed in order to obtain amino acid substitutions within thelacZ-encoded β-galactosidase that result in differences in enzyme activity too small to be detected by ordinary mutant screens. The cryptic substitutions were obtained as spontaneous revertants of nonsense mutations within thelacZgene, and the enzymes differing from wild type were identified by means of polyacrylamide gel electrophoresis or thermal denaturation studies. The relation between enzyme activity and growth rate of these and other mutants supports a model of intermediary metabolism in which the flux of substrate through a metabolic pathway is represented by a concave function of the activity of any enzyme in the pathway. The consequence is that small differences in enzyme activity from wild type result in even smaller changes in fitness.
Properties of spontaneous mitotic recombination occurring in the presence of therad52-1mutation ofSaccharomyces cerevisiae
Authors: Hoekstra Merl F. , Naughton Tom , Malone Robert E.
Published: September 2009

All major recombination pathways in the yeastSaccharomyces cerevisiaerequire theRAD52gene product. We have examined the effect of therad52-1mutation on spontaneous mitotic recombination between heteroalleles, and found that prototrophs are produced at frequencies significantly above reversion. This residual recombination occurs at a relatively uniform level at all of the loci examined. To help understand the role thatRAD52plays in mitotic recombination, we examined recombination between all pairwise combinations of six mutant alleles of theLYS2gene. Therad52-1mutation decreased the variation in amount of recombination between the various pairwise combinations as well as lowering the overall frequency of recombination. The reduced variation results in a different pattern of recombination inrad52-1cells than in wild type. One interpretation of these results is that theRAD52gene product, directly or indirectly, plays a role in the formation or the resolution of mismatches in heteroduplex DNA.
A sex-linked enzyme in a reptile – association with a recent centric fusion in the common lizard
Authors: Goux Jean-Michel , Pasteur Georges
Published: September 2009

In a series ofLacerta viviparasamples from southern France's central mountains, the distribution of genotypes at the mannose phosphate isomerase (MPI) locus has only been accountable as due to sex linkage in female heterogamety, provided the W chromosome carries only one of the two observed alleles in the populations sampled. This is in perfect accordance with cytogenetical data. Reasons are presented that seem to limit acceptable hypotheses for the recent origin of this sex-linked polymorphism to three: a founder effect, a point mutation in Z chromosomes after crossover suppression, or hitch-hiking with the translocation involved.
Models of long term artificial selection in finite population
Authors: Hill William G. , Rasbash Jonathan
Published: September 2009

The effects of population size and selection intensity, which are in the breeder's control, are investigated for ranges of values of quantities outside his control, namely the number, initial distribution of frequencies and effects of genes influencing the trait. Two alleles are assumed to be initially segregating at each locus, with no linkage, dominance or epistasis. The effects are assumed to follow a gamma distribution, using a wide range of its two parameters which specify both mean gene effect or selective value and the shape of the distribution, or the ratio of Wright's effective number to actual number of genes. The initial gene frequencies (q) are assumed to be either 0·5 at all loci, uniformly distributed over the range 0–1, or to have a U-shaped distribution, proportional to [q(1 −q)]−1such as derives from neutral mutation, with gene effect and frequency distributions independent. The mean and variance of selection response and limits, in the absence of new mutation, are derived.

The shape of the distribution of effects is not usually important even up to the selection limit. With appropriate parametrization, the influence of the initial frequency distribution is small over a wide range of parameters. For reasonable choices of parameters, the effects of changing population size from those typically used in animal breeding programmes are likely to be small, but not negligible. For the initial U-shaped frequency distribution, further increases in population size are always expected to give a greater limit, regardless of present value, but not for the other distributions.
Genomic structure of phage F22, a hybrid between serologically and morphologically unrelatedSalmonella typhimuriumbacteriophages P22 andFels 2
Authors: Yamamoto Nobuto , McDonald Robert J.
Published: September 2009

Salmonella typhimuriumphage P22 can recombine with a serologically and morphologically unrelated Salmonella phageFels 2to yield the hybrid phage F22 at a frequency of about 10−12. F22 has inherited the entire late genes (protein coat and tail structural genes) ofFels 2but carries some P22 early genes. P22 genes in the F22 phage were indentified by marker rescue of various P22 mutants. The F22 genome carries thex-erf-c-18-12segment of the P22 genome. A number of P22 amber mutants were also tested to support these data. The F22 region homologous to P22 was mapped by scoring the ratio of P22 backcross recombinant types in lysates of F22 lysogens superinfected with P22c2ts12. The ratio of the distances between these markers and the ends of the homologous region was determined. Furthermore a new F22 hybrid designated F22dis, containing both P22 immunity regions (candIm), was isolated at a frequency of about 10−4by superinfecting F22 lysogens with P22. F22disphage has lost someFels 2gene(s) which have been replaced by the P22 segment containing theImregion, resulting in formation of a defective hybrid phage.
Effect of thebncAgene on the instability ofAspergillus nidulans
Authors: Pizzirani-Kleiner Aline A. , Azevedo J. L.
Published: September 2009

The presence of a gene designatedbncAwhich produces binucleate and trinucleate conidia inA. nidulansalters the instability of disomics, diploids, and strains with chromosome duplication. In disomics, the genebncAincreases instability. In duplicate and diploid strains, thebncAgene reduces instability by acting as a partial stabilizer. In the strain with chromosome duplication, thebncAgene produces increased percentages of bi- and trinucleate conidia, a fact that may be interpreted to be due to the larger conidial volume of this strain or to the combined effect ofbncAand of the strain, which normally already exhibits a small amount of binucleate conidia.
The site of action of the asebia locus (ab) in the skin of the mouse
Authors: Pennycuik Pamela R. , Raphael Kathryn A. , Chapman R. E. , Hardy Margaret H.
Published: September 2009

In mice homozygous for the asebia mutation (abJ/abJ) the sebaceous glands were small and the sebaceous cells abnormal, the fully grown hair follicles were twice as long as those in wild-type (+ / +) mice, the catagen and telogen follicles were abnormal and, because the active phase of the hair cycle was longer than in + / + mice, the initiation of the second hair cycle was delayed. The abnormalities in the sebaceous glands and in catagen and telogen follicles were also present in abJ/abJ embryonic skin grown on a nude host but anagen of the second hair cycle commenced at about the same time in abJ / abJ and + / + grafts. When recombinants incorporating mutant or wild-type epidermis and dermis were grown on a nude host, the abnormalities in the sebaceous glands and the catagen and telogen follicles were only observed in the recombinants incorporating abJ / abJ epidermis. It was concluded that mutant activity in the epidermis was responsible for the abnormalities in the sebaceous glands and in catagen and telogen follicles and that mutant activity at some site distant from the skin was responsible for the abnormalities in the timing of the hair cycles.
An attempt to estimate the effective size of the ancestral species common to two extant species from which homologous genes are sequenced
Authors: Takahata Naoyuki
Published: September 2009

When DNA sequence data on various kinds of homologous genes sampled from two related species are available, there is a way to infer the effective size of their ancestral species, which is a simple consequence of gene genealogical considerations. This method, when applied to the common ancestral species of human and rat, human and mouse, human and bovine, or rodents and bovine estimates their effective sizes all to be of the order of 107, supporting the view that these species indeed shared, around 75 million years ago, a common ancestral species from which they are descended. The effective size thus estimated would imply that the ancestral species was abundant enough to have ample opportunity for adaptive radiation. The extent of silent polymorphism in that species might have been very large, possibly comparable to the number of silent substitutions accumulated in a gene after the mammalian divergence. Some causes that may alter these results and require a more elaborated statistical analysis are discussed.
Evidence for a new major gene influencing meat quality in pigs
Authors: Le Roy Pascale , Naveau J. , Elsen J. M. , Sellier P.
Published: September 2009

The present investigation primarily deals with the inheritance of a pigmeat quality trait, the Napole technological yield (RTN), a measure of cooked weight to fresh weight. This trait as well as lean percentage at 100 kg liveweight and fattening length from 20 to 100 kg liveweight were recorded on 3459 offspring from 67 sires and 433 dams, and 3052 offspring from 64 sires and 405 dams in Penshire (P66) and Pen Ar Lan (P77) composite lines respectively. The hypothesis of a major 2-allele locus contributing to RTN was tested by use of a segregation analysis method. Highly significant likelihood ratios (mixed vs. polygenic transmission models) lead us to conclude that a major gene RN− exerting an unfavourable effect on RTN is segregating in both lines. Maximum likelihood estimates of the parameters under the hypothesis of mixed (monogenic + polygenic) inheritance show that the difference between the means of the 2 homozygotes amounts to about 3 phenotypic standard deviations of the trait, whereas the complete dominance of RN− cannot be rejected. The frequency of RN− is about 0·6 in both lines. These results are discussed in connection with the previously reported ‘Hampshire effect’ on pigmeat quality, as the Hampshire breed is a common component of the foundation stock of the 2 composite lines under study.
Prediction of rates of inbreeding in selected populations
Authors: Wray Naomi R. , Thompson Robin
Published: September 2009

A method is presented for the prediction of rate of inbreeding for populations with discrete generations. The matrix of Wright's numerator relationships is partitioned into ‘contribution’ matrices which describe the contribution of the Mendelian sampling of genes of ancestors in a given generation to the relationship between individuals in later generations. These contributions stabilize with time and the value to which they stabilize is shown to be related to the asymptotic rate of inbreeding and therefore also the effective population size,whereNis the number of individuals per generation and μrandare the mean and variance of long-term relationships or long-term contributions. These stabilized values are then predicted using a recursive equation via the concept of selective advantage for populations with hierarchical mating structures undergoing mass selection. Account is taken of the change in genetic parameters as a consequence of selection and also the increasing ‘competitiveness’ of contemporaries as selection proceeds. Examples are given and predicted rates of inbreeding are compared to those calculated in simulations. For populations of 20 males and 20, 40, 100 or 200 females the rate of inbreeding was found to increase by as much as 75% over the rate of inbreeding in an unselected population depending on mating ratio, selection intensity and heritability of the selected trait. The prediction presented here estimated the rate of inbreeding usually within 5% of that calculated from simulation.
Analysis of lines of mice selected for fat content. 2. Correlated responses in the activities of enzymes involved in lipogenesis
Authors: Hastings Ian M. , Hill William G.
Published: September 2009

Estimates of the activities (Vmax) of six enzymes involved inde novofat synthesis were made in replicated lines of mice differing in fat content. These lines had been selected high and low for 20 generations with three replicates each of Fat, Control and Lean lines and for a further eight generations high and low as an unreplicated line. The activities of ATP-citrate lyase (ACL), acetyl-CoA carboxylase (ACC), fatty acid synthetase (FAS), cytoplasmic malate dehydrogenase (MDH), malic enzyme (ME) and pyruvate kinase (PK) were determinedin vitroin both liver and gonadal fatpad tissues taken at ages five and ten weeks. The activities of ACL, ACC, FAS and ME were significantly higher in the Fat than the Lean lines, and the differences were more pronounced at the earlier age and in the gonadal fatpad where activities in the Fat lines were higher by factors of 3·5, 2·4, 2·5 and 3·5 respectively. The activity of PK was unchanged in each tissue. MDH activity was significantly lower in adipose tissue in the Fat lines than the Lean lines at age ten weeks but not at age five weeks or in liver tissue. Results from replicates indicated that random genetic drift affected enzyme activities but nevertheless significant changes in activity were associated with the direction of selection. The changes in enzyme activity reported here are similar to those known to be associated with major mutations causing obesity in mice.
The use of maternally coded gene products inDrosophila
Authors: Robbins Leonard G.
Published: September 2009

Both maternal and zygotic expression of many essential genes are required for normal development. For some of these genes, absence of maternal function yields striking embryonic defects. The experiments reported here examine two questions about such genes: (1) Are embryonic effects of maternal deficits a common property of maternally-and-zygotically active genes? and (2) Is use of the maternal products of these genes restricted to early embryogenesis? A comparison of times of lethality of mutant sons of normal and mutant-heterozygous mothers has been made for six mutations in thezeste-whiteregion of theDrosophila Xchromosome. Four of the mutations are defective in single cistrons and two are deficiencies that between them remove thirteen essential loci. All of these mutations had previously been shown to have both maternal and zygotic effects, and all of them had been tested, using homozygous germ-line clones, for the effects of complete maternal defects. For several of them, homozygous germ-line clones cause embryonic defects. Of the six, only one,Df(l)K95, shows a shift from larval to embryonic lethality when the mothers are heterozygous, and even in that case lethality occurs at the very end of embryogenesis. These results have two implications: (1) maternally-derived transcripts do not always serve a solely embryonic role; and (2) an embryonic effect of a complete maternal deficit does not by itself demonstrate an embryo-restricted function for the maternal transcript.
Assignment of the mouse desmin gene to chromosome 1 band C3
Authors: Li Zhenlin , Mattei Marie-Geneviève , Mattei Jean-François , Paulin Denise
Published: September 2009

The chromosomal localization of the mouse gene coding for desmin, one of the muscle-specific intermediate filament subunits, was determined byin situhybridization using a specific3H-labelled DNA probe. There is only one copy of the desmin gene and it is located on chromosome 1 in the band C3. This result adds an eleventh locus to a conserved gene cluster and confirms the partial homology that exists between the long arm of human chromosome 2 and chromosome 1 of the mouse.
Analysis of a rare recombination event within the multigenic Hor 2 locus of barley (Hordeum vulgare L.)
Authors: Shewry Peter R. , Parmar Saroj , Franklin Julian , Burgess Shirley R.
Published: September 2009

A rare recombinant within the multigenic Hor 2 locus of barley was detected by SD-PAGE of hordein fractions from F2 grain from the cross Bomi × P12/3. Analysis of a homozygous F4 line by 2-D IEF/SDS-PAGE showed that recombination between the class I/II and class III subfamilies of genes had occurred, indicating that they are spatially separate within the Hor 2 locus. RFLP analysis using a B hordein-related cDNA clone confirmed that recombination had occurred, while similar analysis using a genomic clone related to γ-type hordein (encoded by the Hor 5/HrdF locus) indicated the order of the two subfamilies of genes on the short arm of chromosome 5, the class I/II genes being closer to the centromere. The results are consistent with the origin of the B hordein gene family from initial duplication of a single ancestral gene to give two genes which diverged to become the ancestors of the class I/II and class III subfamilies. Subsequent cycles of duplication and divergence have resulted in the present high degree of polymorphism.
Elevated galactosyltransferase activity ont-bearing sperm segregates with T/t-complex distorter loci-2
Authors: Shur Barry D. , Scully Natalie F.
Published: September 2009

Sperm bearing completet-haplotypes are preferentially transmitted during fertilization from heterozygous +/tmales, often in excess of 95% relative to their +-bearing meiotic partner. Sperm fromt-bearing males have an approximate two- to fourfold increase in β1, 4-galactosyltransferase (GalTase) activity, a cell surface protein that mediates sperm binding to the egg zona pellucida. The elevated GalTase activity strictly correlates with the preferential transmission oft-sperm from +/tmales, since eight other enzymes show normal levels of activity ont-sperm. Furthermore, sperm bearing proximal partialt-haplotypes, which are no longer favoured during fertilization, have normal levels of GalTase activity. Nevertheless, it has been unclear whether the elevated sperm GalTase activity ont-sperm is due to specific loci in the distal segment of the T/t-complex, or rather, is an indirect consequence of the abnormal sperm function characteristic of +/tandtx/tymales. In this study, it is shown that the elevated sperm GalTase activity is due specifically to factors that reside within the distal segment of the T/t complex, which also containsTcd-2, the strongest of the distorter loci. Since the structural locus for GalTase is located on mouse chromosome 4, these results also show that T/t-complex alleles on chromosome 17 are regulatory in nature and affect the expression of sperm surface components critical for normal fertilization. Models are presented to explain how elevated GalTase activity could contribute to sperm transmission distortion.
The effect of biased conversion on the mutation load
Authors: Bengtsson Bengt O.
Published: September 2009

The mutation load is sensitive to changes in the segregation ratio caused, for example, by biased conversion. If the distortion, measured by the force of conversion, is greater than the loss of fitness in the mutation heterozygotes, then the mutation load will be far away from its normal value. Examples are given where a small positive bias together with realistic fitness parameters increase the mutation load by more than two orders of magnitude.

In practical terms this implies that great restrictions should be placed on the use of substances and treatments that may induce mutations associated with a positive conversion bias.
Selection response in traits with maternal inheritance
Authors: Lande Russell , Kirkpatrick Mark
Published: September 2009

Maternal inheritance is the non-Mendelian transmission of traits, from mothers to their offspring. Despite its presence in virtually all organisms, acting through a variety of mechanisms, the evolutionary consequences of maternal inheritance are not well understood. Here we review and extend a model of the inheritance and evolution of multiple quantitative characters with complex pathways of maternal effects. Extensions of the earlier model include common family environmental effects not associated with maternal phenotype, sexual dimorphism, and paternal effects (non-Mendelian influence of the father on offspring traits). We find that, in contrast to simple Mendelian inheritance, maternal inheritance produces qualitatively different evolutionary dynamics for two reasons: (1) the response to selection on a set of characters depends not only on their additive genetic variances and covariances, but also on maternal characters that influence them, and (2) time lags in the response to selection create a form of evolutionary momentum. These results have important implications for evolution in natural populations and practical applications in the economic improvement of domesticated species. We derive selection indices that maximize either the economic improvement in a single generation of artificial selection or the asymptotic rate of improvement in long-term selection programmes, based on individual merit or a combination of individual and family merit. Numerical examples show that accounting for maternal inheritance can lead to considerable increases in the efficiency of artificial selection.
Mutation-selection balance and the evolutionary advantage of sex and recombination
Authors: Charlesworth Brian
Published: September 2009

Mutation-selection balance in a multi-locus system is investigated theoretically, using a modification of Bulmer's infinitesimal model of selection on a normally-distributed quantitative character, taking the number of mutations per individual (n) to represent the character value. The logarithm of the fitness of an individual withnmutations is assumed to be a quadratic, decreasing function ofn. The equilibrium properties of infinitely large asexual populations, random-mating populations lacking genetic recombination, and random-mating populations with arbitrary recombination frequencies are investigated. With ‘synergistic’ epistasis on the scale of log fitness, such that log fitness declines more steeply asnincreases, it is shown that equilibrium mean fitness is least for asexual populations. In sexual populations, mean fitness increases with the number of chromosomes and with the map length per chromosome. With ‘diminishing returns’ epistasis, such that log fitness declines less steeply asnincreases, mean fitness behaves in the opposite way. Selection on asexual variants and genes affecting the rate of genetic recombination in random-mating populations was also studied. With synergistic epistasis, zero recombination always appears to be disfavoured, but free recombination is disfavoured when the mutation rate per genome is sufficiently small, leading to evolutionary stability of maps of intermediate length. With synergistic epistasis, an asexual mutant is unlikely to invade a sexual population if the mutation rate per diploid genome greatly exceeds unity. Recombination is selectively disadvantageous when there is diminishing returns epistasis. These results are compared with the results of previous theoretical studies of this problem, and with experimental data.
A newt-complex embryonic lethal (tcl0) has arisen in theThpchromosome of the mouse and is allelic tot0
Authors: Sanchez Edwin R. , Hammerberg Craig
Published: September 2009

Complement testing of aThpline revealed a failure of survival ofThp/t0embryos. The genetic factor responsible for this lethality maps between Brachyury (T) and tufted (tf) on the murine seventeenth chromosome. This lethal factor permits recombination betweenTandtfand does not affect the transmission of its seventeenth chromosome. Its effect upon embryonic development is similar to that of thet0haplotype. It would appear to represent a point mutation of a single gene,t-complex lethal zero(tcl0).
Cattanach's translocation [Is(7:X)Ct] corrects male sterility due to homozygosity for chromosome 7 deletions
Authors: Erickson Robert P.
Published: September 2009

Mice carrying particular deletions of chromosomal material at and around the colour (C) locus on chromosome 7 (c3H/c6H) are viable but sterile. An insertional translocation of chromosome 7 into theX(Cattanach's) has been previously used to rescue females carrying deletions of chromosome 7 which are ordinarily lethal. We studied the ability of this translocation to correct the sterility found in the presence of the two partially complementing deletions. We predicted that the sterility would be corrected in females who would be mosaics because of X-inactivation. The result in males was uncertain since the sterility had been shown to be due to defective spermatogenesis, and the X chromosome is inactivated early in the course of spermatogenesis. Thec3H/c6Hmale and female deletional sterility were rescued by Cattanach's translocation.
Variation in the shape of the mouse mandible: 1. Effect of age and sex on the results obtained from the discriminant functions used for genetic monitoring
Authors: Lovell D. P. , Totman P. , Johnson F. M.
Published: September 2009

The shape of the mandible of the mouse can be described by a series of discriminant functions which have been used to discriminate between and investigate relationships among strains of mice. The effect of sex and variation in age of the animal on the results obtained from these functions has been investigated. Significant sex differences in mandible shape were detected, but these were considerably smaller than the differences found between two inbred strains. A simple correction for expressing each measure as a proportion of the sum of the measures on each bone removes the effects of overall size. Significant age effects were found, but these were only large in animals under seven weeks of age where considerable changes are taking place in the relative lengths of bone measurements. Routine testing for genetic authenticity using the shape of the mandible is possible over a wide age range and may be an efficient method for monitoring genotypes at the end of long-term experiments.
Two locally acting genetic controls of gene conversion,ccf-5andccf-6, inAscobolus immersus
Authors: Howell W. M. , Lamb B. C.
Published: September 2009

Two new conversion control factors (ccfs),ccf-5andccf-6, have been characterized in the Pasadena strains ofAscobolus immersus. Both are monogenic, with two known allelic forms (calledAandB) of each factor, and affect the frequency of meiotic gene conversion at awhite(w) ascospore locus closely linked to it,ccf-5affectingw-9andccf-6affectingw-BHj. Theccfs appear to be specific to their own target site, with no effect on at least nine unlinkedwmutations. Conversion of thewlocus affected was studied in + ×wcrosses with all four possibleccfarrangements: for example, for + ×w-9, withccf-5(A) in both parents, withccf-5(B) in both parents, withccf-5(A) in +,Binw-9, and withccf-5(B) in +,Ainw-9. For bothccfs, there were slight differences between crosses homozygous forAand those homozygous forB, and also slight differences between the two forms of heterozygous cross,A/BandB/A, but the major effect was for heterozygosity for the control factor to depress conversion frequency of thewlocus, compared with either homozygous state. These twoccfs are compared with other sites affecting recombination in fungi and higher eukaryotes. Two possible modes of action ofccfs5and6are (i) on pairing closeness before hybrid DNA initiation, and (ii) on later stages such as the spread of hybrid DNA from an initiation point.
Genetic and environmental modification of gene expression in thebrlA12variegated position effect mutant ofAspergillus nidulans
Authors: Clutterbuck A. J. , Spathas D. H.
Published: September 2009

ThebrlA12variegated position effect mutant is particularly suited for tests of environmental and genetic influences on variegation, but out of a large number of substances added to the medium, only salts at high concentrations and methylamine significantly increased expression of this gene. Medium shifting experiments showed thatbrlA12activity could be switched on late, but once active, was rarely switched off again during conidiation. SeparatebrlA12clones in heterokaryons were activated independently. SomebrlA12-specific suppressor mutants, including those at loci giving almost complete suppression, have been studied. One class of suppressors also confers inability to utilize galactose as carbon source and comparison with other, pre-existing mutants showed that thebrlA12phenotype was either suppressed or enhanced by mutants with complex phenotypes involving galactose utilization, molybdate resistance, acid phosphatase production and sulphur metabolism. Tests for the involvement of DNA methylation inbrlA12expression gave negative results.
AnSD(Segregation Distribution) –MR(Male Recombination) chromosome isolated from a natural population ofDrosophila melanogaster
Authors: Bencze Gábor , Slatko Barton E.
Published: September 2009

A second chromosome line ofDrosophila melanogaster(S-90), isolated from a northern California natural population, is able to induce (1) an increased frequency of X-chromosome visible mutations, (2) male recombination activity subject to reciprocal cross suppression, and (3) strong meiotic drive from heterozygous males. Based upon several lines of evidence (including the response to suppressor chromosomes of both systems) we conclude thatS-90contains bothSD(Segregation Distortion) andMR(PorI) chromosome activity. The two systems appear to behave independently and simultaneously, and a small centromeric region of theS-90chromosome appears to contain the major genetic elements of both systems.
The DNA transposition system of hybrid dysgenesis inDrosophila melanogastercan function despite defects in host DNA repair
Authors: Slatko Barton E. , Mason James M. , Woodruff R. C.
Published: September 2009

Genetic traits associated with the hybrid dysgenesis syndrome were quantified in strains deficient in two major host-coded DNA repair pathways, post-replication and excision repair. A defect in either (or both) pathway(s) fails to influence the frequency of male recombination or sex-linked recessive lethal mutations associated with hybrid dysgenesis, suggesting that the DNA transposable elements associated with this syndrome act independently of these cellular functions. However, when the post-replication repair pathway is blocked, the recovery of second chromosomes containing factors associated with hybrid dysgenesis activity is reduced. The decrease in recovery is associated with zygotic lethality.
Two-way within-family and mass selection for 8-week body weight in different mouse populations
Authors: von Butler Ines , Willeke Henning , Pirchner Franz
Published: September 2009

Two mouse populations, randombred albino mice and a cross of four inbred strains, were divergently selected for high (H8) and low (L8) 8-week body weight over 18 generations using within-family and individual selection. The crossbreds showed asymmetry of selection response and realized heritabilities (H80·29 ± 0·01; L80·17 ± 0·01). In the randombred population realized heritabilities were symmetrical (H80·23 ± 0·01; L80·22 ± 0·02). Over the first nine generations individual selection was nearly 40 per cent better than within-family selection, as was expected from the full sib correlation in both populations. As selection progressed, within-family selection reached 82% and 61% of the responses obtained with individual selection in the crossbreds and randombred respectively. Correlated responses for 3-week (weaning) and 5-week body weights agreed with observations made on direct responses, but selection for L8did not reduce weaning weight. Selection for L8decreased and selection for H8increased first litter size at birth. However, mass-selected L8-pairs had a higher life-reproduction and life-span than H8-pairs.
Potential for hitchhiking in theeda-edd-zwfgene cluster ofEscherichia coli
Authors: Dykhuizen Daniel E. , De Framond Jean , Hartl Daniel L.
Published: September 2009

The locieda, eddandzwfform a tightly linked cluster inE. colithat functions in the metabolism of galacturonate, gluconate and glucose. This cluster has been transferred from six natural isolates into the genetic background ofE. coliK12 and examined with regard to effects on growth rate in chemostats. Although the naturally occurringedaandzwfalleles are selectively neutral, theeddalleles are not. Theeddalleles fall into three functional classes distinguished by their effects on growth rate in gluconate medium, the most common classes differing in fitness by approximately 1% per hour. This extensive non-neutral genetic variation ofeddis discussed in light of the evident rarity of gluconate as a natural substrate. We propose that gluconate selection is intermittent in space or time, providing the population an opportunity to accumulate non-neutral genetic variants during periods of relaxed selection. Such genetic variants will eventually be sorted out by the intermittent periods of gluconate selection, and during these periods the linkededaandzwfalleles will experience pronounced hitchhiking effects.
Variance-effective population number: the effects of sex ratio and density on the mean and variance of offspring numbers in the flour beetle,Tribolium castaneum
Authors: Wade Michael J.
Published: September 2009

I report the results of an experimental study of the effects of sex ratio and density on the mean and variance in offspring numbers in both sexes of the flour beetle,Tribolium castaneum. The variance-effective number is estimated from the observed variance in offspring numbers using the methods of Crow & Morton (1955).

Both the mean and the variance in offspring numbers were found to vary with sex ratio and density; as was found in previous studies (Wade, 1980), males were generally more variable in offspring numbers than females. The ratio of variance to mean progeny numbers in each sex was approximately unity at all sex ratios.
Effects of a temperature-sensitiveMinutemutation on gene expression inDrosophila melanogaster
Authors: Sinclair Donald A. R. , Grigliatti Thomas A. , Kaufman Thomas C.
Published: September 2009

Minute(M) lesions exhibit a striking propensity for interacting with many different mutations. In the past, few attempts have been made to explain these diverse phenomena. This study describes a variety of temperature-sensitive (ts) interactions exhibited by the ts third chromosomeMinutemutationM(3)LS4Q-III(Q-III). Most of these interactions (i.e. those involvingvg, cp, Dl, DfdorLy) reflectQ-III-induced enhancement of the respective mutant phenotypes at the restrictive temperature. However,Q-IIIalso suppresses the extra-sex-comb phenotypes ofPcandMscat 29 °C and evokes lethal and bristle traits when combined withJ34eat the restrictive temperature. All of these interactions are characteristic of non-tsMinutelesions and thus they appear to be correlated with general physiological perturbations associated with theMsyndrome. In addition, our findings show that mutations that affect ribosome production and/or function, namelysu(f)ts67gandbbts−1, exhibit interactions comparable to those elicited byQ-III. Hence, in accordance with previous findings, we argue that most of theQ-IIIinteractions can be attributed to reduced translational capacity at the restrictive temperature. Finally, reciprocal temperature shift studies were used to delineate TSPs for interactions betweenQ-IIIandvg(mid to late second instar),cp(about mid-third instar),Dfd(early third instar) andDl(late second to mid third instar). We believe that these TSPs represent developmental intervals during which the respective gene products are utilized.