bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for random distribution of sequence variants inTenebrio molitorsatellite DNA
Authors: Plohl Miroslav , Borˇstnik Branko , Lucijanić-Justić Vlatka , Ugarković ÐurÐica
Published: September 2009

Tenebrio molitorsatellite DNA has been analysed in order to study sequential organization of tandemly repeated monomers, i.e. to see whether different monomer variants are distributed randomly over the whole satellite, or clustered locally. Analysed sequence variants are products of single base substitutions in a consensus satellite sequence, producing additional restriction sites. The ladder of satellite multimers obtained after digestion with restriction enzymes was compared with theoretical calculations and revealed the distribution pattern of particular monomer variants within the satellite. A defined higher order repeating structure, indicating the existence of satellite subfamilies, could not be observed. Our results show that some sequence variants are very abundant, being present in nearly 50 % of the monomers, while others are very rare (0-1 % of monomers). However, the distribution of either very frequent, or very rare sequence variants inT. molitorsatellite DNA is always random. Monomer variants are randomly distributed in the total satellite DNA and thus spread across all chromosomes, indicating a relatively high rate of sequence homogenization among different chromosomes. Such a distribution of monomer variants represents a transient stage in the process of sequence homogenization, indicating the high rate of spreading in comparison with the rate of sequence variant amplification.
Distribution and structure of cloned P elements from theDrosophila melanogasterP strain π2
Authors: O'Hare Kevin , Driver Alan , McGrath Stephen , Johnson-Schiltz Dena M.
Published: September 2009

P transposable elements ofDrosophila melanogastercloned from the strong P strain π2have been analysed. The structures and chromosomal locations of 26 of the 30–50 elements estimated to be present in π2 have been determined. At one location two elements are inserted 100 base pairs (bp) apart, and in a second location two elements are only separated by the 8 bp duplicated upon P-element insertion. In addition to 2.9 kilobasepair (kbp) elements, elements with 14 different internal deletions from 1.3 to 2.3 kbp in size have been isolated. There are 7 copies of the 2–9 kbp element, 2 copies each of 5 internally deleted elements and a single copy of 9 internally deleted elements. One of the elements found twice is the KP element, which may play a role in the regulation of hybrid dysgenesis in strains which contain many copies of this element. Apart from internal deletions the elements are extremely homogeneous in DNA sequence, with only 2 single base polymorphisms detected twice each in over 16 kbp of P-element sequence. Although transpositions are infrequent in an inbred P cytotype strain such as π2, the distribution of these cloned elements indicates that when the genomic library was made, the strain was polymorphic with respect to element location. The distribution and structures of the element are discussed with respect to models for regulation of P-element transposition.
Polymorphisms distinguishing different mouse species andthaplotypes
Authors: Horiuchi Yoshihito , Agulnik Alexander , Figueroa Felipe , Tichy Herbert , Klein Jan
Published: September 2009

Three anonymous chromosome 17 DNA markers,D17Tu36,D17Tu43, and D17Le66B, differentiate between house mouse species and/or betweentchromosomes. TheD17Tu36probe, which maps near theFulocus and to theIn(17)4ontchromosomes, identifies at least 15 haplotypes, each haplotype characterized by a particular combination of DNA fragments obtained after digestion with theTaqI restriction endonuclease. Ten of these haplotypes occur inMus domesticus, while the remaining five occur inM. musculus. In each of these two species, one haplotype is borne bytchromosomes while the other haplotypes are present on non-r chromosomes. TheD17Tu43probe, which maps near theD17Leh122locus and to theIn(17)3ontchromosomes, also identifies at least 15 haplotypes inTaqI DNA digests, of which nine occur in M. domesticus and six inM. musculus. One of the nineM. domesticushaplotypes is borne bytchromosomes, the other haplotypes are borne by non-f chromosomes; two of the sixM. musculushaplotypes are borne bytchromosomes and the remaining four by non-f chromosomes. Some of theD17Tu43haplotypes are widely distributed in a given species, while others appear to be population-specific. Exceptions to species-specificity are found only in a few mice captured near theM. domesticus-M. musculushybrid zone or in t chromosomes that appear to be of hybrid origin. TheD17Leh66Bprobe, which maps to theIn(17)2, distinguishes three haplotypes ofM. domesticus-dznved t chromosomes and one haplotype ofM. musculus-derivzd t chromosomes. Because of these characteristics, the three markers are well suited for the study of mouse population genetics in general and of t chromosome population genetics in particular. A preliminary survey of wildM. domesticusandM. musculuspopulations has not uncovered any evidence of widespread introgression of genes from one species to the other; possible minorintrogressions were found only in the vicinity of the hybrid zone. Typing of inbred strains has revealed the contribution of onlyM. domesticusDNA to the chromosome 17 of the laboratory mouse.
Dominant hemimelia andEn-1on mouse chromosome 1 are not allelic
Authors: Higgins Maureen , Hill Robert E. , West John D.
Published: September 2009

Previous studies have shown thatEn-1, a homeobox-containing gene, maps close to or at theDhlocus in the mouse. Since homeobox-containing genes are key genes in the control of development the close proximity ofEn-1to the developmentally significant geneDhraised the possibility that theDhmutation represented a mutant allele ofEn-1. A genetic analysis involvingEn-1,Dh, and other chromosome 1 markers (Emv-17,InandPep-3) shows that althoughDhandEn-1are closely linked they are separable by recombination (4/563). The likely gene order and recombination frequencies of these loci are: In (5.2±0.9)Emv-17(1.1±0.4) Dh (0.7±0.4)En-1(3.0±0.7) Pep-3. This shows thatDhis not a mutant allele ofEn-1.
The role of DNA replication and isochores in generating mutation and silent substitution rate variance in mammals
Authors: Walker Adam Eyre
Published: September 2009

It has been suggested that isochores are maintained by mutation biases, and that this leads to variation in the rate of mutation across the genome. A model of DNA replication is presented in which the probabilities of misincorporation and proofreading are affected by the composition and concentration of the free nucleotide pools. The relationship between sequenceG + Ccontent and the mutation rate is investigated. It is found that there is very little variation in the mutation rate between sequences of differentG + Ccontents if the total concentration of the free nucleotides remains constant. However, variation in the mutation rate can be arbitrarily large if some mismatches are proofread and the total concentration of free nucleotides varies. Hence the model suggests that the maintenance of isochores by the replication of DNA in free nucleotide pools of biased composition does not leadper seto mutation rate variance. However, it is possible that changes in composition could be accompanied by changes in concentration, thus generating mutation rate variance. Furthermore, there is the possibility that germ-line selection could lead to alterations in the overall free nucleotide concentration through the cell cycle. These findings are discussed with reference to the variance in mammalian silent substitution rates.
The distribution of transposable elements within and between chromosomes in a population ofDrosophila melanogaster. II. Inferences on the nature of selection against elements
Authors: Charlesworth Brian , Lapid Angela , Canada Darlene
Published: September 2009

Data were collected on the distribution of nine families of transposable elements among a sample of autosomes isolated from a natural population ofDrosophila melanogaster, by means ofin situhybridization of biotinylated probes to polytene chromosomes. There is no general tendency for elements to accumulate at the tips of chromosomes. Elements tend to be present in excess of random expectation in the euchromatin proximal to the centromeres of the major autosomes, and on chromosome four. There is considerable heterogeneity between different families in the extent of this excess. The overall abundance of element families is inversely related to the extent to which they accumulate proximally. The level of proximal accumulation for the major autosomes is similar to that on the fourth chromosome, but less than that for the X chromosome. There is an overall deficiency of elements in the mid-section of the X compared with the mid-sections of the major autosomes, with considerable heterogeneity between families. The magnitude of this deficiency is positively related to the extent to which elements accumulate proximally. No such deficiency is seen if the proximal regions of the X and autosomes are compared. There is a small and non-significant excess of elements in third chromosomes carrying inversions. There is some between-year heterogeneity in element abundance. The implications of these findings are discussed, and it is concluded that they generally support the hypothesis that transposable element abundance is regulated primarily by the deleterious fitness consequences of meiotic ectopic exchange between elements. If this is the case, such exchange must be very infrequent in the proximal euchromatin, and the elements detected in population surveys of this kind must be inserted into sites where they have negligible mutational effects on fitness.
Aspects of maximum likelihood methods for the mapping of quantitative trait loci in line crosses
Authors: Knott S. A. , Haley C. S.
Published: September 2009

Maximum likelihood methods for the mapping of quantitative trait loci (QTL) have been investigated in an F2population using simulated data. The use of adjacent (flanking) marker pairs gave improved power for the detection of QTL over the use of single markers when markers were widely spaced and the QTL effect large. The use of flanking marker loci also always gave moreaccurate and less biassed estimates for the effect and position of the QTL and made the method less sensitive to violations of assumptions, for example non-normality of the distribution. Testing the hypothesis of a linked QTL against that of no QTL is not biassed by the presence of unlinked QTL. This test is more robust and easier to obtain than the comparison of a linked with an unlinked QTL. Fixing the recombination fraction between the markers at an incorrect value in the analyses with flanking markers does not generally bias the test for QTL or estimates of their effect. The presence of multiple linked QTL bias both tests and estimates of effect with interval mapping, leading to inflated values when QTL are in association in the lines crossed and deflated values when they are in dispersion.
Electrofusion of mouse embryos results in uniform tetraploidy and not tetraploid/diploid mosaicism
Authors: James Roberta M. , Kaufman Matthew H. , Webb Sheila , West John D.
Published: September 2009

Some previous attempts to produce tetraploids experimentally have resulted in a proportion of treated embryos becoming 2n/4n mosaics at a frequency which may be as high as 20%, when using cytochalasin B as a fusigenic stimulus and cytogenetic techniques to identify putative tetraploid embryos. To investigate the possible occurrence of 4n/2n mosaicism, tetraploid embryos were produced by electrofusion, a process which allows adjacent blastomeres at the 2-cell stage to fuse following exposure to electric field pulses. Embryos used for electrofusion were hemizygous for a transgene consisting of approximately 1000 copies of the mouse β-globin gene. Afterin situhybridization, one hybridization signal is expected per diploid genome. Tetraploid cells in 7·5-, 8·5-, 9·5- and 10·5-day-old conceptuses were distinguished from diploid cells by performingin situhybridization on histological sections. The frequency of nuclei with two hybridization signals in the ‘hemizygous’ tetraploid embryos was compared to diploid embryos which were either hemizygous or homozygous for the β-globin transgene. Comparison of the frequency of nuclei with two hybridization signals between tissues of ‘hemizygous’ tetraploid conceptuses and homozygous diploid conceptuses showed no significant difference, which implies that the tissues in the tetraploid conceptuses were uniformly tetraploid. No evidence was found to suggest that electrofusion results in 2n/4n mosaicism.
Studies of linkage in populations. X. Altitude and autosomal gene arrangements inDrosophila robusta
Authors: Levitan Max , Scheffer Sonja J.
Published: September 2009

Data are presented concerning the gene arrangements in the second and third chromosomes ofDrosophila robustain eight altitudinal transects. A consistent change is the increase in the arrangement 2L-3, particularly in the linkage combination2L-3.2R, with increasing altitude. The reciprocal decrease with increasing altitude affects several different 2-left arrangements, most consistently 2L-1. The arrangements of 2-right show no significant variation with altitude, and those of 3-right do so only in a few samples of the two northern transects studied, none in any of the southern ones. These results confirm previous evidence for the significant role of the arrangements of the left arm of the second chromosome in the adaptations of this species to altitude and suggest further that interactions of linked arrangements are involved in these adaptations. The data also indicate that the factors responsible for the altitudinal adaptations of this species are in many cases not the same ones that are responsible for variations in its gene arrangements with latitude.
Mitochondrial DNA analysis of introgression between adjacent taxa of rock-wallabies,Petrogalespecies (Marsupialia: Macropodidae)
Authors: Bee C. A. , Close R. L.
Published: September 2009

Simple, inexpensive techniques were used to analyse the mtDNA of nine chromosomally distinct populations ofPetrogale. Eight of these populations occur in sequence along the Great Dividing Range of eastern Australia; six have been described as species. Diagnostic mtDNA morphs were found throughout the latitudinal ranges of four of the described species. A fifth morph spanned the ranges of two described species and three additional taxa which have been designated chromosome races. These five mtDNA morphs, and others with local distributions, were used to assess interactions between the taxa. Limited introgression was indicated across the chromosomal boundaries ofP. penicillata/P. herbertiandP. inornata/P. assimilis; atypical mtDNA morphs were found within theP. herbertiandP. inornatachromosomal distributions. No introgression was detected betweenP. herbertiandP. inornata, whose distributions are separated by the Fitzroy River. Nor was there evidence of recent contact betweenP. assimilis,P. herbertiandP. purpureicollis, despite the late occupancy of parts of the intervening area by unidentifiedPetrogale. These data, considered in the light of information obtained from previous studies on chromosomes, allozymes and parasites, have contributed to the decision to consider all the eastern representatives of thelateralis-penicillatagroup ofPetrogaleas being specifically distinct from each other.
The role of growth hormone in lines of mice divergently selected on body weight
Authors: Hastings Ian M. , Bootland Lorna H. , Hill William G.
Published: September 2009

An understanding of the physiological and genetic changes which determine the response to selection is critical for both evolutionary theory and to assess the application of new molecular techniques to commercial animal breeding. We investigated an aspect of physiology, growth hormone (GH) metabolism, which mighta priorihave been expected to play a large part in the response of mouse lines selected for high or low body weight. Disruption of endogenous GH or addition of exogenous GH had similar proportionate effects on body weight in both lines of mice (although differences in body composition arose) suggesting that neither the production of GH nor receptor sensitivity to GH had been altered as a result of selection. This supports a ‘pleiotropic model’ of the response to selection: that many genes with diverse metabolic roles all contribute to the divergent phenotype. This result has significant commercial implications as it suggests that artificial selection, transgenic technology and environmental manipulation may be synergistic rather than antagonistic strategies.
Spontaneous mutation for a quantitative trait inDrosophila melanogaster. I. Response to artificial selection
Authors: López María A. , López-Fanjul Carlos
Published: September 2009

Divergent selection for abdominal bristle number was carried out for 47 generations, starting from a completely homozygous population ofDrosophila melanogaster. All lines were selected with the same proportion (20%) but at two different numbers of selected parents of each sex (5 or 25). A significant response to selection was obtained in 25 lines (out of 40). In most cases, it could be wholly attributed to a single mutation of relatively large effect (> 0·3 phenotypic standard deviations). A total number of 30 mutations were detected. In agreement with theory, larger responses in each direction were achieved by those lines selected at greater effective population sizes. A large fraction of mutations were lethals (10/30). Thus, the observed divergence between lines of the same effective size selected in opposite directions was smaller than expected under neutrality. The ratio of new mutational variance to environmental variance was estimated to be(0·52±0·09)×10−3.
Genetic structure and differentiation inMetrosideros polymorpha(Myrtaceae) along altitudinal gradients in Maui, Hawaii
Authors: Aradhya K. M. , Mueller-Dombois D. , Ranker T. A.
Published: September 2009

The level and distribution of genetic variability within and amongMetrosideros polymorphapopulations along altitudinal gradients on the island of Maui, Hawaii were examined to assess the extent of genetic differentiation. Sixteen loci encoding 11 enzymes were scored in 17 populations along the NE wet slope of Mt. Haleakala and Kipahulu Valley in East Maui and six populations along the Puu Kukui trail in West Maui. On average, 50% of the loci were polymorphic within populations with an overall mean of 2·15 alleles per locus. The observed heterozygosities for different populations were moderate (0·108–0·220) and conformed to panmixia except for one of the mid-elevation populations. The distribution of allozyme variation indicates that very little differentiation has occurred along altitudinal gradients. Approximately 90% of the total variation resides within populations in East Maui while 95% was found within West Maui populations. The mean populational pair-wise genetic identities (Nei's I) ranged from 0·909 to 0·998. The UPGMA cluster analysis on genetic identity matrices and PCA on allele frequencies revealed marginal altitudinal differentiation. Twenty one alleles out of a total 63 showed statistically significant correlations with environmental variables.
Mapping and characterization ofP-element-induced mutations at quantitative trait loci inDrosophila melanogaster
Authors: Lai Chaoqiang , Mackay Trudy F. C.
Published: September 2009

Xchromosomes derived from crosses of inbred P and MDrosophila melanogasterstrains that had extreme effects on abdominal and/or sternopleural bristle number in males, were further analyzed to determine their effects in females and to map the loci at which the mutations occurred. Seven lines that had on average 3.9 fewer sternopleural bristles than wildtype in males had average homozygous sternopleural bristle effects of −2·2. The bristle effects were partially recessive, with an average degree of dominance of −0·60. Physical mapping of the sternopleural bristle effects of these lines placed them all at approximately 24·7 cM. These mutations are apparently allelic on the basis of a complementation test, and deficiency mapping indicates they occur within chromosomal bands 8A4; 8C6.In situhybridization analysis of the sites ofPelement insertions of these lines suggests that mutations probably resulted from excision ofPelements at 8C on the original inbred P strain chromosome. Two additional lines, NDC(19) and DP(146), had reduced numbers of sternopleural and abdominal bristles. NDC(19) males had 9·7 fewer abdominal and 8·6 fewer sternopleural bristles than wildtype. The corresponding homozygous abdominal and sternopleural bristle number effects were −5·8 and −3·8, respectively; with the abdominal bristle effect completely recessive and the sternopleural bristle effect nearly additive. DP(146) males had 6·2 fewer abdominal and 4·1 fewer sternopleural bristles than wildtype, with homozygous abdominal bristle effects of −4·3 and sternopleural bristle effects of −2·0. Abdominal bristle effects of this line were partially recessive whereas the sternopleural bristle effects were additive. Physical mapping showed effects on both bristle traits segregated jointly in these two lines, with the NDC(19) mutation closely linked toyand the DP(146) mutation 0·17 cM from it. Complementation tests and deficiency mapping also indicate the mutations in lines NDC(19) and DP(146) are at closely linked but separate loci within chromosomal bands 1B2; 1B4–6 and 1B4–6; 1B10 respectively, with some epistatic effects.In situhybridization analysis of sites ofPelement insertion suggest that the NDC(19) mutation, which may be ascuteallele, was probably caused by aPelement insertion in the IB region; the DP(146) mutation is also associated with an insertion at IB.
Evolution of the mitochondrial ATPase 6 gene in Drosophila: unusually high level of polymorphism in D. melanogaster
Authors: Kaneko Maki , Satta Yoko , Matsuura Etsuko T. , Chigusa Sadao I.
Published: September 2009

We have determined 1990 bp mitochondrial DNA sequence which extends from 3′ end of the cytochrome oxidase subunit I (COI) gene to 5′ end of the COIII gene from two sibling species of Drosophila, D. simulans and D. mauritiana. Analyses of the sequences and part of the NADH dehydrogenase subunit 2 gene and the COI gene together with those from D. melanogaster and D. yakuba revealed that amino-acid substitution rate of the ATPase 6 gene seems to be higher in some strains of D. melanogaster than in the other species. High level of amino-acid polymorphism in this gene was observed in D. melanogaster. Synonymous substitution rate is relatively constant in all the genes examined, suggesting that mutation rate is not higher in the ATPase 6 gene of D. melanogaster. The amino-acid substitutions found specifically in D. melanogaster are at the sites which are not conserved among mammals, yeast and E. coli. These sites of the ATPase 6 gene might lose the selective constraint in D. melanogaster, and the amino-acid substitutions can be explained by neutral mutations and random genetic drift.
Directional selection and the evolution of sex and recombination
Authors: Charlesworth Brian
Published: September 2009

Models of the evolutionary advantages of sex and genetic recombination due to directional selection on a quantitative trait are analysed. The models assume that the trait is controlled by many additive genes. A nor-optimal selection function is used, in which the optimum either moves steadily in one direction, follows an autocorrelated linear Markov process or a random walk, or varies cyclically. The consequences for population mean fitness of a reduction in genetic variance, due to a shift from sexual to asexual reproduction are examined. It is shown that a large reduction in mean fitness can result from such a shift in the case of a steadily moving optimum, under light conditions. The conditions are much more stringent with a cyclical or randomly varying environment, especially if the autocorrelation for a random environment is small. The conditions for spread of a rare modifier affecting the rate of genetic recombination are also examined, and the strength of selection on such a modifier determined. Again, the case of a steadily moving optimum is most favourable for the evolution of increased recombination. The selection pressure on a recombination modifier when a trait is subject to strong truncation selection is calculated, and shown to be large enough to account for observed increases in recombination associated with artificial selection. Theoretical and empirical evidence relevant to evaluating the importance of this model for the evolution of sex and recombination is discussed.
The genetics of the Luria–Latarjet effect in bacteriophage T4: evidence for the involvement of multiple DNA repair pathways
Authors: Hyman Paul
Published: September 2009

The Luria-Latarjet effect is an increase in resistance of a virus to DNA damage during infection of a host. It has often been assumed to involve recombinational repair, but this has never been demonstrated experimentally. Using nine bacteriophage (phage) T4 mutants, I present evidence indicating that, for phage T4, the Luria-Latarjet effect is due to three repair pathways-excision repair, post-replication-recombinational-repair (PRRR) and multiplicity reactivation (MR) (a second form of recombinational repair). The results also show that the Luria-Latarjet effect develops in two stages. The first stage starts soon after infection. Damage which occurs during the first stage can be repaired by excision repair or PRRR. The second stage appears to start after the first round of DNA replication is complete. DNA damage which occurs during this stage can apparently be repaired by MR as well as the other two repair pathways. The results of this study support the hypothesis that recombinational repair has been selected to ensure that the progeny phage genomes which are packaged have minimum DNA damage. Since other viruses which infect bacterial, animal and plant cells show a Luria-Latarjet effect similar to that in phage T4, the conclusions from this study may have wide applicability.
Correction of chlorophyll deficiency in alloplasmic male sterileBrassica junceathrough recombination between chloroplast genomes
Authors: Kirti P. B. , Narasimhulu S. B. , Mohapatra T. , Prakash S. , Chopra V. L.
Published: September 2009

Brassica junceacv. Pusa Bold carryingB. oxyrrhinacytoplasm (oxycytoplasm) was male sterile and chlorotic under field conditions at low temperature (Prakash & Chopra, 1990). Leaf protoplasts of the chlorotic male sterile alloplasmic line (2n = 36) were fused with hypocotyl protoplasts of green male fertile,B. junceacv. RLM-198 (2n = 36) using polyethylene glycol. Of the 1043 plants regenerated from 10 fusion experiments, 123 had ‘gigas’ features and were identified as presumptive fusion products. Among field-grown population, one plant was dark green even at low temperatures and male sterile. It possessed 72 chromosomes which formed 36 bivalents at late diakinesis of meiosis-I. This plant was back-crossed toB. junceacv. Pusa Bold (the maintainer line) for three successive generations. One male sterile, normal green BC3 progeny plant with 2n = 36 was analyzed for organelle constitution. Probing its total DNA with the mitochondrial gene for cytochrome oxidase subunit I revealed that it possessed mitochondria ofB. oxyrrhina. Southern hybridization pattern with the gene for ribulose bisphosphate carboxylase oxygenase-large subunit (rbcL) revealed that the chloroplast genome of the chlorophyll deficiencycorrected plant had characteristics of bothB. junceaandB. oxyrrhina. The deficiency correction has been attributed to recombination between chloroplast genomes of the two species.
Dosage dependent modifiers ofwhitealleles inDrosophila melanogaster
Authors: Sabl Joy F. , Birchler James A.
Published: September 2009

As part of a study to identify dosage-sensitive modifiers of thewhiteeye colour locus and the retrotransposon, copia, a segmental aneuploid screen was conducted. It surveys the autosomal complement of the genome for dosage dependent modifiers ofwhite, including ones effective upon retrotransposon insertion-induced alleles. Several regions were found which, when present as a segmental trisomy, affected one or more of the alleles tested in a strong and consistent fashion. Two of these regions have been identified as containing previously described modifiers,Darkener of-apricotandInverse regulator-a. The remainder identify newwhiteallele modifiers. Selected segmental monosomics were also tested where possible for regions exhibiting a trisomic effect. At least three regions were found to have a dosage-dependent effect in one, two and three copies.
Heritabilities of growth curve parameters and age-specific expression of genetic variation under two different feeding regimes in Japanese quail (Coturnix coturnix japonica)
Authors: Gebhardt-Henrich Sabine G. , Marks Henry L.
Published: September 2009

This study investigated genetic variation in growth and final size in relationship to differences in heritabilities under good and poor feeding conditions. Heritabilities of growth and final size were estimated for several traits underad libitumand restricted feeding conditions. A 30% feed restriction from hatching to 44 days of age in Japanese quail chicks decreased body weight and tarsus length at 44 days of age and the length of the third primary covert feather at 24 days of age relative to controls fedad libitum. Wing length at 44 days of age was not significantly different forad libitumfed and restricted quail. Genetic variances for body weight and tarsus length were very large throughout growth which resulted in heritability estimates close to one for these traits. The genetic correlations among feeding treatments were low, indicating that different genes were affecting growth under the two treatments. Growth was described by the components: asymptote, growth period, and shape of the growth curve following the modified Richards growth curve model (Brisbinet al.1986). Tarsus length, which had high heritability of the parameter ‘growth period’ of the model, tended to display a higher heritability under the restriction than underad libitumfeeding. Body weight and feather length, which had either no heritable or low heritable ‘growth periods’ estimates, tended to be more heritable underad libitumfeeding. The shape parameter of the growth curve was not heritable for any trait, except tarsus length under restricted feeding.
Do self-fertilization and genetic drift promote a very low genetic variability in the allotetraploidBulinus truncatus(Gastropoda: Planorbidae) populations?
Authors: Njiokou Flobert , Bellec Christian , Berrebi Patrick , Delay Bernard , Jarne Philippe
Published: September 2009

Bulinus truncatus, one of the intermediate hosts of the genusSchistosomais an hermaphrodite freshwater snail species occupying a variety of environments over almost all Africa. These environments are subjected to large variations in water availability.B. truncatusis allotetraploid and its populations exhibit various frequencies of aphallic individuals (unable to reproduce as male). Both traits probably favour a reproduction by self-fertilization. Here we investigate the genetic structure of populations ofB. truncatusof Niger and Ivory Coast using protein electrophoresis to analyse the influence of the environment and of both the last traits. To obtain an estimate of the true heterozygosity in this allotetraploid species, we analyse independently the two diploid loci at each tetraploid locus. Our study indicates (i) an extremely low intrapopulation polymorphism with most alleles fixed and the total absence of heterozygotes and (ii) low differentiation between populations. These results indicate high gene flow between populations. However, the existence of private alleles sometimes at high frequency, the low polymorphism and the lack of heterozygotes point to the role of both genetic drift and self-fertilization, the second amplifying the genetic consequences of the first.
The use of retrotransposons as markers for mapping genes responsible for fitness differences between relatedDrosophila melanogasterstrains
Authors: Nuzhdin Sergey V. , Keightley Peter D. , Pasyukova Elena G.
Published: September 2009

Hitch-hiking of dispersed mobile elements serving as molecular markers was used as a new tool for mapping quantitative trait loci inDrosophila melanogaster. TwoDrosophilastrains with high fitness (HA) were backcrossed repeatedly to a closely related strain with low fitness (LA) to initiate experimental populations with expected HA gene frequencies of 1/32. The frequencies of 19 insertion sites of the retrotransposonsmdg1andcopiawere analyzed after 11 to 17 generations. Frequencies of sites from the HA line increased substantially in the pericentromeric region, indicating that one or more loci responsible for the fitness difference between the strains were located there. A maximum likelihood (ML) procedure was applied to estimate selection coefficients associated with the markers, and this indicated a broad, strongly selected region of the chromosome. At least one additional locus was localized in the middle of the 2L arm. Possible applications of this method are discussed.
The probability of fixation of a favoured allele in a subdivided population
Authors: Barton N. H.
Published: September 2009

In a stably subdivided population with symmetric migration, the chance that a favoured allele will be fixed is independent of population structure. However, random extinction introduces an extra component of sampling drift, and reduces the probability of fixation. In this paper, the fixation probability is calculated using the diffusion approximation; comparison with exact solution of the discrete model shows this to be accurate. The key parameters are the rates of selection, migration and extinction, scaled relative to population size (S = 4Ns, M = 4Nm, Λ = 4Nλ); results apply to a haploid model, or to diploids with additive selection. If new colonies derive from many demes, the fixation probability cannot be reduced by more than half. However, if colonies are initially homogeneous, fixation probability can be much reduced. In the limit of low migration and extinction rates (M, Λ ≪ 1), it is 2s/{1 + (Λ/MS)(1 −exp(−S))}, whilst in the opposite limit (S≪ 1), it is 4sM/{Λ(Λ +M)}. In the limit of weak selection (M, Λ ≫ 1), it is 4sM/{Λ(Λ +M)}. These factors are not the same as the reduction in effective population size (Ne/N), showing that the effects of population structure on selected alleles cannot be understood from the behaviour of neutral markers.
Inheritance of a meiotic abnormality that causes the ovulation of primary oocytes and the production of digynic triploid mice
Authors: West John D. , Webb Sheila , Kaufman Matthew H.
Published: September 2009

Previous studies have demonstrated that the LT/SvKau strain of mice ovulates a high proportion of oocytes as diploid primary oocytes rather than secondary oocytes. These ovulated primary oocytes are arrested at meiotic metaphase I but may be fertilized to produce digynic triploid embryos. In the present study, 40·4% of eggs analysed from LT/SvKau females were ovulated as primary oocytes, compared to 1·2% from control C57BL/Ws strain mothers. These two inbred strains were intercrossed to produce eight sets of Fl, F2 and backcross females and the frequency of triploidy was investigated. The results are compatible with segregation of a co-dominant, autosomal gene that has a major influence on the incidence of triploidy. We suggest that the provisional gene symbolPoo(primary oocyte ovulation) be assigned to this gene, with allelesPool(the ‘mutant’ allele present in the LT/SvKau strain) andPoob(the normal allele present in C57BL/Ws mice).Poois incompletely penetrant and has variable expressivity because the proportion of oocytes ovulated as primary oocytes by LT/SvKau mice was variable and, in some cases, nil. In putativePool/Poobheterozygotes the frequency of ovulated primary oocytes was increased only marginally (from 1·2% to 66%) by the presence of one copy of thePoolallele, but this increase was found consistently (in two reciprocal Fl crosses) and was statistically significant. No evidence was found for tight genetic linkage betweenPooand two Mendelian loci (brown on chromosome 4 and glucose phosphate isomerase on chromosome 7), that were segregating in the crosses. ThePoolmutant in the LT/SvKau strain of mice provides a valuable resource to study the cell and molecular biology of mammalian oocyte maturation and the control of meiosis.
Detection of quantitative trait loci from frequency changes of marker alleles under selection
Authors: Keightley Peter D. , Bulfield Grahame
Published: September 2009

A method was developed to estimate effects of quantitative trait loci (QTL) by maximum likelihood using information from changes of gene frequency at marker loci under selection, assuming an additive model of complete linkage between markers and QTL. The method was applied to data from 16 molecular and coat colour marker loci in mouse lines derived from the F2of two inbred strains which were divergently selected on 6-week weight for 21 generations. In 4 regions of the genome, marker allele frequencies were more extreme than could be explained by sampling, implying selection at nearby QTL. An effect of about 0·5 standard deviations was located on chromosome 11, and accounted for nearly 10% of the genetic variance in the base population. QTL with effects as small as 0·2 phenotypic standard deviations could be detected. For typing of a given number of individuals, the power of detection of QTL is very high compared to, for example, analysis of an F2 population. The joint effects of linkage and selection were investigated by Monte Carlo simulation. Marker gene frequencies change little as a consequence of selection at a QTL unless the marker and QTL are less than about 20 cM apart.
Prediction of long-term contributions and inbreeding in populations undergoing mass selection
Authors: Woolliams J. A. , Wray N. R. , Thompson R.
Published: September 2009

For a population undergoing mass selection, derived from an unselected base population in generation zero, the expected long-term contribution to the population of an ancestor from generation 1 was shown to be equal to that expected during random selection multiplied by(whereis one half the breeding value of the ancestor for the trait under selection standardized by the phenotypic standard deviation,ithe intensity of selection, andis the competitiveness which is defined bythe heritability in generation 2 andkthe variance reduction coefficient). It was shown that the rate of inbreeding (ΔF) could be partitioned into three components arising from expected contributions, sampling errors and sampling covariances respectively. Using this result ΔFwas derived and shown to be dominated by terms that describe ΔFby variance of family size in a single generation plus a term that accounts for the expected proliferation of lines over generations from superior ancestors in generation 1. The basic prediction of ΔFwas given by

whereMandFare the numbers of breeding males and females,Tthe number of offspring of each sex,ρmand ρtare correlations among half-sibs in generation 2 for males and females respectively, andKis a function of the intensity and competitiveness.
Differences inPelement population dynamics between the sibling speciesDrosophila melanogasterandDrosophila simulans
Authors: Kimura Kiyoshi , Kidwell Margaret G.
Published: September 2009

Patterns ofPelement establishment and evolution were compared in populations of D.melanogasterand D.simulans. For each species, mixed populations were initiated withMstrain flies lackingPelements together withPstrain flies having similarPelement copy numbers and phenotypes. The mixed populations were subsequently maintained under similar environmental conditions. On the basis of gonadal sterility assays,Pelements tended to be significantly more active inD.melanogasterthan inD.simulanspopulations. This activity difference between the two species was positively associated withPelement copy number, determined by restriction enzyme analysis, and transposition frequency, as determined by a transposition assay. Host factors are the most likely explanation for the observed species variation. Difficulty of establishment may be a factor determining the absence ofPelements in natural populations ofD.simulans.
Sources of information for estimating heritability from selection experiments
Authors: Thompson R. , Atkins K. D.
Published: September 2009

Maximum likelihood estimation methods with an individual animal model were used to analyse a bi-directional selection experiment, with control, for cannon bone length in Scottish Blackface sheep. A method is described for partitioning the likelihood to allow within- and between-line estimates of genetic variance. It is concluded that both sources of information made substantial contributions to the precision of the base population heritability estimate. The implications for different experimental designs and varying heritability are discussed.
Error thresholds and stationary mutant distributions in multi-locus diploid genetics models
Authors: Higgs Paul G.
Published: September 2009

We study multi-locus models for the accumulation of disadvantagenous mutant alleles in diploid populations. The theory used is closely related to the quasi-species theory of molecular evolution. The stationary mutant distribution may either be localized close to a peak in the fitness landscape or delocalized throughout sequence space. In some cases there is a sharp transition between these two cases known as an error threshold. We study a multiplicative fitness landscape where the fitness of an individual withjhomozygous mutant loci andkheterozygous loci iswjk= (1 −s)j(1 −hs)k. For a sexual population in this landscape there are two types of solution separated by an error threshold. For a parthenogenetic population there may be three types of solution and two error thresholds for some values ofh. For a population reproducing by selfing the solution is independent ofh, since the frequency of heterozygous individuals is negligible. The mean fitnesses of the populations depend on the reproductive method even for the multiplicative landscape. The sexual may have a higher or lower fitness than the parthenogen, depending on the values ofhandu/s. Selfing leads to a higher mean fitness than either sexual reproduction or parthenogenesis. We also study a fitness landscape with epistatic interactions withwjk= exp(−s(2j+k)α). The sexual population has a higher fitness than the parthenogen when α > 1. This confirms previous theories that sexual reproduction is advantageous in cases of synergistic epistasis. The mean fitness of a selfing population was found to be higher than both the sexual and the parthenogen over the range of parameter values studied. We discuss these results in relation to the theory of the evolution of sex. The fitness of the stationary distribution in cases where unfavourable mutations accumulation is one factor which could explain the observed prevalence of sexual reproduction in natural populations, although other factors may be more important in many cases.
Evolution ofCastanea sativaMill, in Turkey and Europe
Authors: Villani F. , Pigliucci M. , Cherubini M.
Published: September 2009

The evolution of sweet chestnut (Castanea sativaMill.) appears to be a complex mixture of long-range gene flow, natural and artificial selection, and local effects of isolation by distance. In this paper we present the most complete analysis to date on the genetic structure and variability of 52 populations of chestnut spanning the entire European area of distribution. The study is based on the use of isozyme data. Our samples came from four major zones, possibly representing relevant steps in the evolution and spread of sweet chestnut in Europe: (i) eastern Turkey, the supposed center of origin of the species; (ii) western Turkey, the area in which human domestication started; (iii) Italy, where domesticated chestnut was first introduced to the rest of Europe by the Romans; and (iv) France, representing the latest phases of the expansion, close to the northern limit of the taxon.

As previous studies based only on Italian and some Turkish populations suggested, the electrophoretic data are consistent with a series of episodes of west- and north-ward migration. The early expansion from the center of origin was probably slow, resulting from natural diffusion of the species. Most of the original genetic variation has been conserved during this phase. Successive episodes of colonization of western Turkey and then of the rest of Europe were probably the more rapid result of human activity. These later stages were associated with genetic drift that reduced the overall heterozygosity of the extant populations. No evidence for selection could be found at the large geographical scale of this study, although previous regional works have shown spatial patterns of allelic frequencies at a few loci and phenotypic differentiation consistent with the action of past selective pressures.
Genetic contribution to sex determination in turtles with environmental sex determination
Authors: Girondot Marc , Zaborski Patrick , Servan Jean , Pieau Claude
Published: September 2009

In many reptiles, sex determination is temperature-sensitive. This phenomenon has been shown to take place in the laboratory as well as in nature, but its effect on natural populations remains questionable. In the turtleEmys orbicularis, the effects of temperature override a weak mechanism of genetic sex determination which is revealed in incubation at pivotal temperature. At this temperature, the sexual phenotype is concordant with the expression of the serologically defined H-Y antigen (H-Ys) in non-gonadal tissues; males are H-Ys negative (H-Y−) whereas females are H-Ys positive (H-Y+). To estimate the importance of sexual inversion (sexual phenotype and H-Ys expression discordant) in populations of Brenne (France), the frequencies of male and female sexual phenotypes among H-Ys phenotypes were determined. The frequencies of sex reversed individuals are low, only 6 % of phenotypic females being H-Y−and 11 % of phenotypic males being H-Y+. According to these data, two theoretical models have been constructed to estimate the contribution to sex determination of individuals in relation to their genotype. The first model excludes any influence of incubation temperature and sexual phenotype on the fitness of individuals. The second one considers that these parameters influence fitness because this model has been previously shown to favour environmental sex determination. In both models, it appears that sex determination can be viewed as genotypic and monogenic with some individuals sexually inverted by theaction of temperature. One category of homozygous animals differentiates mainly into one sex, and the heterozygous animals differentiate mainly into the other sex. The second category of homozygotes has a low frequency in the populations and can differentiate as male or female without high constraint. Then it is estimated that in Brenne approximately 83% of the eggs are incubated in conditions allowing the genetic component to influence sex determination.