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See detailA Forward Genetic Screen Identifies Mutants Deficient for Mitochondrial Complex I Assembly in Chlamydomonas Reinhardtii.
Barbieri, M. R.; Larosa, Véronique ULg; Nouet, Cécile ULg et al

in Genetics (2011), 188

Mitochondrial Complex I is the largest multimeric enzyme of the respiratory chain. The lack of a model system with facile genetics has limited the molecular dissection of Complex I assembly. Using ... [more ▼]

Mitochondrial Complex I is the largest multimeric enzyme of the respiratory chain. The lack of a model system with facile genetics has limited the molecular dissection of Complex I assembly. Using Chlamydomonas reinhardtii as an experimental system to screen for Complex I defects, we isolated, via forward genetics, amc1 to 7 nuclear mutants (for assembly of mitochondrial complex I) displaying reduced or no Complex I activity. BN-PAGE and immunoblot analyses revealed that amc3 and amc4 accumulate reduced levels of the Complex I holoenzyme (950 kDa) while all other amc mutants fail to accumulate a mature complex. In amc1, 2, 5, 6, 7, the detection of a 700 kDa subcomplex retaining NADH dehydrogenase activity indicates an arrest in the assembly process. Genetic analyses established that amc5 and amc7 are alleles of the same locus while amc1 to 4 and amc6 define distinct complementation groups. The locus defined by the amc5 and amc7 alleles corresponds to the NUOB10 gene, encoding PDSW, a subunit of the membrane arm of Complex I. This is the first report of a forward genetic screen yielding the isolation of Complex I mutants. This work illustrates the potential of using Chlamydomonas as a genetically-tractable organism to decipher Complex I manufacture. [less ▲]

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See detailA hidden markov model combining linkage and linkage disequilibrium information for haplotype reconstruction and quantitative trait locus fine mapping.
Druet, Tom ULg; Georges, Michel ULg

in Genetics (2010), 184(3), 789-98

Faithful reconstruction of haplotypes from diploid marker data (phasing) is important for many kinds of genetic analyses, including mapping of trait loci, prediction of genomic breeding values, and ... [more ▼]

Faithful reconstruction of haplotypes from diploid marker data (phasing) is important for many kinds of genetic analyses, including mapping of trait loci, prediction of genomic breeding values, and identification of signatures of selection. In human genetics, phasing most often exploits population information (linkage disequilibrium), while in animal genetics the primary source of information is familial (Mendelian segregation and linkage). We herein develop and evaluate a method that simultaneously exploits both sources of information. It builds on hidden Markov models that were initially developed to exploit population information only. We demonstrate that the approach improves the accuracy of allele phasing as well as imputation of missing genotypes. Reconstructed haplotypes are assigned to hidden states that are shown to correspond to clusters of genealogically related chromosomes. We show that these cluster states can directly be used to fine map QTL. The method is computationally effective at handling large data sets based on high-density SNP panels. [less ▲]

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See detailOn the evolution and expression of Chlamydomonas reinhardtii nucleus-encoded transfer RNA genes
Cognat, Valerie; Deragon, Jean*-Marc; Vinogradova, Elizaveta et al

in Genetics (2008), 179(1), 113-123

In Chlamydomonas reinhardtii, 259 tRNA genes were identified and classified into 49 tRNA isoaccepting families. By constructing phylogenetic trees, we determined the evolutionary history for each tRNA ... [more ▼]

In Chlamydomonas reinhardtii, 259 tRNA genes were identified and classified into 49 tRNA isoaccepting families. By constructing phylogenetic trees, we determined the evolutionary history for each tRNA gene family. The majority of the IRNA sequences are more closely related to their plant counterparts than to animals ones. Northern experiments also permitted LIS to show that at least one member of each IRNA isoacceptor family is transcribed and correctly processed in vivo. A short stretch of T residues known to be a signal for termination of polymerase III transcription was found downstream of most IRNA genes. It allowed us to propose that the vast majority of the IRNA genes are expressed and to confirm that numerous IRNA genes separated by short spacers are indeed cotranscribed. Interestingly, in silico analyses and hybridization experiments show that the cellular IRNA abundance is correlated with the number of tRTNA genes and is adjusted to the codon usage to optimize translation efficiency. Finally, we studied the origin of SINEs, short interspersed elements related to tRNAs, whose presence in Chlamydomonas is exceptional. Phylogenetic analysis strongly suggests that tRNA(Asp)-related SINEs originate front a prokaryotic-type IRNA either horizontally transferred from a bacterium or originally present in mitochondria or chloroplasts. [less ▲]

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See detailFine mapping of quantitative trait loci affecting female fertility in dairy cattle on BTA03 using a dense single-nucleotide polymorphism map.
Druet, Tom ULg; Fritz, Sebastien; Boussaha, Mekki et al

in Genetics (2008), 178(4), 2227-35

Fertility quantitative trait loci (QTL) are of high interest in dairy cattle since insemination failure has dramatically increased in some breeds such as Holstein. High-throughput SNP analysis and SNP ... [more ▼]

Fertility quantitative trait loci (QTL) are of high interest in dairy cattle since insemination failure has dramatically increased in some breeds such as Holstein. High-throughput SNP analysis and SNP microarrays give the opportunity to genotype many animals for hundreds SNPs per chromosome. In this study, due to these techniques a dense SNP marker map was used to fine map a QTL underlying nonreturn rate measured 90 days after artificial insemination previously detected with a low-density microsatellite marker map. A granddaughter design with 17 Holstein half-sib families (926 offspring) was genotyped for a set of 437 SNPs mapping to BTA3. Linkage analysis was performed by both regression and variance components analysis. An additional analysis combining both linkage analysis and linkage-disequilibrium information was applied. This method first estimated identity-by-descent probabilities among base haplotypes. These probabilities were then used to group the base haplotypes in different clusters. A QTL explaining 14% of the genetic variance was found with high significance (P < 0.001) at position 19 cM with the linkage analysis and four sires were estimated to be heterozygous (P < 0.05). Addition of linkage-disequilibrium information refined the QTL position to a set of narrow peaks. The use of the haplotypes of heterozygous sires offered the possibility to give confidence in some peaks while others could be discarded. Two peaks with high likelihood-ratio test values in the region of which heterozygous sires shared a common haplotype appeared particularly interesting. Despite the fact that the analysis did not fine map the QTL in a unique narrow region, the method proved to be able to handle efficiently and automatically a large amount of information and to refine the QTL position to a small set of narrow intervals. In addition, the QTL identified was confirmed to have a large effect (explaining 13.8% of the genetic variance) on dairy cow fertility as estimated by nonreturn rate at 90 days. [less ▲]

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See detailOn the detection of imprinted QTL in line crosses: effect of linkage disequilibrium
Sandor, Cynthia ULg; Georges, Michel ULg

in Genetics (2008), 180

Imprinted quantitative trait loci (QTL) are commonly reported in studies using line-cross designs, especially in livestock species. It was previously shown that such parent-of-origin effects might result ... [more ▼]

Imprinted quantitative trait loci (QTL) are commonly reported in studies using line-cross designs, especially in livestock species. It was previously shown that such parent-of-origin effects might result from the nonfixation of QTL alleles in one or both parental lines, rather than from genuine molecular parental imprinting. We herein demonstrate that if linkage disequilibrium exists between marker loci and nonfixed QTL, spurious detection of pseudo-imprinting is increased by an additional 40-80% in scenarios mimicking typical livestock situations. This is due to the fact that imprinting can be tested only in F(2) offspring whose sire and dam have distinct marker genotypes. In the case of linkage disequilibrium between markers and QTL, such parents have a higher chance to have distinct QTL genotypes as well, thus resulting in distinct padumnal and madumnal allele substitution effects, i.e., QTL pseudo-imprinting. [less ▲]

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See detailRmd9p controls the processing/stability of mitochondrial mRNAs and its overexpression compensates for a partial deficiency of oxa1p in Saccharomyces cerevisiae.
Nouet, Cécile ULg; Bourens, Myriam; Hlavacek, Otakar et al

in Genetics (2007), 175(3), 1105-15

Oxa1p is a key component of the general membrane insertion machinery of eukaryotic respiratory complex subunits encoded by the mitochondrial genome. In this study, we have generated a respiratory ... [more ▼]

Oxa1p is a key component of the general membrane insertion machinery of eukaryotic respiratory complex subunits encoded by the mitochondrial genome. In this study, we have generated a respiratory-deficient mutant, oxa1-E65G-F229S, that contains two substitutions in the predicted intermembrane space domain of Oxa1p. The respiratory deficiency due to this mutation is compensated for by overexpressing RMD9. We show that Rmd9p is an extrinsic membrane protein facing the matrix side of the mitochondrial inner membrane. Its deletion leads to a pleiotropic effect on respiratory complex biogenesis. The steady-state level of all the mitochondrial mRNAs encoding respiratory complex subunits is strongly reduced in the Deltarmd9 mutant, and there is a slight decrease in the accumulation of two RNAs encoding components of the small subunit of the mitochondrial ribosome. Overexpressing RMD9 leads to an increase in the steady-state level of mitochondrial RNAs, and we discuss how this increase could suppress the oxa1 mutations and compensate for the membrane insertion defect of the subunits encoded by these mRNAs. [less ▲]

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See detailNo accelerated rate of protein evolution in male-biased Drosophila pseudoobscura genes.
Metta, Muralidhar ULg; Gudavalli, Rambabu; Gibert, Jean-Michel et al

in Genetics (2006), 174(1), 411-20

Sexually dimorphic traits are often subject to diversifying selection. Genes with a male-biased gene expression also are probably affected by sexual selection and have a high rate of protein evolution. We ... [more ▼]

Sexually dimorphic traits are often subject to diversifying selection. Genes with a male-biased gene expression also are probably affected by sexual selection and have a high rate of protein evolution. We used SAGE to measure sex-biased gene expression in Drosophila pseudoobscura. Consistent with previous results from D. melanogaster, a larger number of genes were male biased (402 genes) than female biased (138 genes). About 34% of the genes changed the sex-related expression pattern between D. melanogaster and D. pseudoobscura. Combining gene expression with protein divergence between both species, we observed a striking difference in the rate of evolution for genes with a male-biased gene expression in one species only. Contrary to expectations, D. pseudoobscura genes in this category showed no accelerated rate of protein evolution, while D. melanogaster genes did. If sexual selection is driving molecular evolution of male-biased genes, our data imply a radically different selection regime in D. pseudoobscura. [less ▲]

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See detailFine mapping and physical characterization of two linked quantitative trait loci affecting milk fat yield in dairy cattle on BTA26.
Gautier, Mathieu; Barcelona, Rosa Roy; Fritz, Sebastien et al

in Genetics (2006), 172(1), 425-36

Previously, a highly significant QTL affecting fat yield and protein yield and mapped to the bovine BTA26 chromosome has been reported to segregate in the French Holstein cattle population. To confirm and ... [more ▼]

Previously, a highly significant QTL affecting fat yield and protein yield and mapped to the bovine BTA26 chromosome has been reported to segregate in the French Holstein cattle population. To confirm and refine the location of this QTL, the original detection experiment was extended by adding 12 new families and genotyping 25 additional microsatellite markers (including 11 newly developed markers). Data were then analyzed by an approach combining both linkage and linkage disequilibrium information, making it possible to identify two linked QTL separated by 20 cM corresponding to approximately 29 Mb. The presence of a QTL affecting protein yield was confirmed but its position was found to be more telomeric than the two QTLunderlying fat yield. Each identified QTL affecting milk fat yield was physically mapped within a segment estimated to be <500 kb. Two strong functional candidate genes involved, respectively, in fatty acid metabolism and membrane permeability were found to be localized within this segment while other functional candidate genes were discarded. A haplotype comprising the favorable allele at each QTL position appears to be overrepresented in the artificial insemination bull population. [less ▲]

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See detailThe role of the bovine growth hormone receptor and prolactin receptor genes in milk, fat and protein production in Finnish Ayrshire dairy cattle.
Viitala, Sirja; Szyda, Joanna; Blott, Sarah et al

in Genetics (2006), 173(4), 2151-64

We herein report new evidence that the QTL effect on chromosome 20 in Finnish Ayrshire can be explained by variation in two distinct genes, growth hormone receptor (GHR) and prolactin receptor (PRLR). In ... [more ▼]

We herein report new evidence that the QTL effect on chromosome 20 in Finnish Ayrshire can be explained by variation in two distinct genes, growth hormone receptor (GHR) and prolactin receptor (PRLR). In a previous study in Holstein-Friesian dairy cattle an F279Y polymorphism in the transmembrane domain of GHR was found to be associated with an effect on milk yield and composition. The result of our multimarker regression analysis suggests that in Finnish Ayrshire two QTL segregate on the chromosomal region including GHR and PRLR. By sequencing the coding sequences of GHR and PRLR and the sequence of three GHR promoters from the pooled samples of individuals of known QTL genotype, we identified two substitutions that were associated with milk production traits: the previously reported F-to-Y substitution in the transmembrane domain of GHR and an S-to-N substitution in the signal peptide of PRLR. The results provide strong evidence that the effect of PRLR S18N polymorphism is distinct from the GHR F279Y effect. In particular, the GHR F279Y has the highest influence on protein percentage and fat percentage while PRLR S18N markedly influences protein and fat yield. Furthermore, an interaction between the two loci is suggested. [less ▲]

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See detailLinkage disequilibrium on the bovine X chromosome: Characterization and use in quantitative trait locus mapping
Sandor, Cynthia ULg; Farnir, Frédéric ULg; Hansoul, Sarah ULg et al

in Genetics (2006), 173(3), 1777-1786

We herein demonstrate that in the Holstein-Friesian dairy cattle population, microsatellites are as polymorphic on the X chromosome as on the autosomes but that the level of linkage disequilibrium between ... [more ▼]

We herein demonstrate that in the Holstein-Friesian dairy cattle population, microsatellites are as polymorphic on the X chromosome as on the autosomes but that the level of linkage disequilibrium between these markers is higher on the X chromosome than on the autosomes. The latter observation is not compatible with the small male-to-female ratio that prevails in this population and results in a higher gonosomal than autosomal effective population size. It suggests that the X chromosome undergoes distinct selective or mutational forces. We describe and characterize a novel Markovian approach to exploit this linkage disequilibrium to compute the probability that two chromosomes are identical-by-descent conditional on flanking marker data. We use the ensuing probabilities in a restricted maximum-likelihood approach to search for quantitative trait loci (QTL) affecting 48 traits of importance to the dairy industry and provide evidence for the presence of QTL affecting 5 of these traits on the bovine X chromosome. [less ▲]

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See detailHaplotype sharing refines the location of an imprinted quantitative trait locus with major effect on muscle mass to a 250-kb chromosome segment containing the porcine IGF2 gene
Nezer, C.; Collette, C.; Moreau, L. et al

in Genetics (2003), 165(1), 277-285

We herein describe the fine mapping of an imprinted QTL with major effect on muscle mass that was previously assigned to distal SSC2p in the pig. The proposed approach exploits linkage disequilibrium in ... [more ▼]

We herein describe the fine mapping of an imprinted QTL with major effect on muscle mass that was previously assigned to distal SSC2p in the pig. The proposed approach exploits linkage disequilibrium in combination with QTL genotyping by marker-assisted segregation analysis. By identifying a haplotype shared by all "Q" chromosomes, we map the QTL to an approximately 250-kb chromosome segment containing INS and IGF2 as the only known paternally expressed genes. This considerably reinforces the candidacy of these genes, justifying their detailed analysis. [less ▲]

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See detailMolecular dissection of a quantitative trait locus: a phenylalanine-to-tyrosine substitution in the transmembrane domain of the bovine growth hormone receptor is associated with a major effect on milk yield and composition.
Blott, Sarah; Kim, Jong-Joo; Moisio, Sirja et al

in Genetics (2003), 163(1), 253-66

We herein report on our efforts to improve the mapping resolution of a QTL with major effect on milk yield and composition that was previously mapped to bovine chromosome 20. By using a denser chromosome ... [more ▼]

We herein report on our efforts to improve the mapping resolution of a QTL with major effect on milk yield and composition that was previously mapped to bovine chromosome 20. By using a denser chromosome 20 marker map and by exploiting linkage disequilibrium using two distinct approaches, we provide strong evidence that a chromosome segment including the gene coding for the growth hormone receptor accounts for at least part of the chromosome 20 QTL effect. By sequencing individuals with known QTL genotype, we identify an F to Y substitution in the transmembrane domain of the growth hormone receptor gene that is associated with a strong effect on milk yield and composition in the general population. [less ▲]

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See detailMosaicism of Solid Gold supports the causality of a noncoding A-to-G transition in the determinism of the callipyge phenotype.
Smit, Maria; SEGERS, Karin ULg; Carrascosa, Laura Garcia et al

in Genetics (2003), 163(1), 453-6

To identify the callipyge mutation, we have resequenced 184 kb spanning the DLK1-, GTL2-, PEG11-, and MEG8-imprinted domain and have identified an A-to-G transition in a highly conserved dodecamer motif ... [more ▼]

To identify the callipyge mutation, we have resequenced 184 kb spanning the DLK1-, GTL2-, PEG11-, and MEG8-imprinted domain and have identified an A-to-G transition in a highly conserved dodecamer motif between DLK1 and GTL2. This was the only difference found between the callipyge (CLPG) allele and a phylogenetically closely related wild-type allele. We report that this SNP is in perfect association with the callipyge genotype. The demonstration that Solid Gold-the alleged founder ram of the callipyge flock-is mosaic for this SNP virtually proves the causality of this SNP in the determinism of the callipyge phenotype. [less ▲]

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See detailSimultaneous mining of linkage and linkage disequilibrium to fine map quantitative trait loci in outbred half-sib pedigrees: Revisiting the location of a quantitative trait locus with major effect on milk production on bovine chromosome 14
Farnir, Frédéric ULg; Grisart, B.; Coppieters, Wouter ULg et al

in Genetics (2002), 161(1), 275-287

A maximum-likelihood QTL mapping method that simultaneously exploits linkage and linkage disequilibrium and that is applicable in outbred half-sib pedigrees is described. The method is applied to fine map ... [more ▼]

A maximum-likelihood QTL mapping method that simultaneously exploits linkage and linkage disequilibrium and that is applicable in outbred half-sib pedigrees is described. The method is applied to fine map a QTL with major effect on milk fat content in a 3-cM marker interval on proximal BTA14. This proximal location is confirmed by applying a haplotype-based association method referred to as recombinant ancestral haplotype analysis. The origin of the discrepancy between the QTL position derived in this work and that of a previous analysis is examined and shown to be due to the existence of distinct marker haplotypes associated with QTL alleles having large substitution effects. [less ▲]

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See detailMutants of Chlamydomonas reinhardtii deficient in mitochondrial complex I: Characterization of two mutations affecting the nd1 coding sequence
Remacle, Claire ULg; Baurain, Denis ULg; Cardol, Pierre ULg et al

in Genetics (2001), 158(3), 1051-60

The mitochondrial rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) comprises more than 30 subunits, the majority of which are encoded by the nucleus. In Chlamydomonas reinhardtii, only five ... [more ▼]

The mitochondrial rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) comprises more than 30 subunits, the majority of which are encoded by the nucleus. In Chlamydomonas reinhardtii, only five components of complex I are coded for by mitochondrial genes. Three mutants deprived of complex I activity and displaying slow growth in the dark were isolated after mutagenic treatment with acriflavine. A genetical analysis demonstrated that two mutations (dum20 and dum25) affect the mitochondrial genome whereas the third mutation (dn26) is of nuclear origin. Recombinational analyses showed that dum20 and dum25 are closely linked on the genetic map of the mitochondrial genome and could affect the nd1 gene. A sequencing analysis confirmed this conclusion: dum20 is a deletion of one T at codon 243 of nd1; dum25 corresponds to a 6-bp deletion that eliminates two amino acids located in a very conserved hydrophilic segment of the protein. [less ▲]

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See detailA Rank-Based Nonparametric Method for Mapping Quantitative Trait Loci in Outbred Half-Sib Pedigrees: Application to Milk Production in a Granddaughter Design
Coppieters, Wouter ULg; Kvasz, A.; Farnir, Frédéric ULg et al

in Genetics (1998), 149(3), 1547-55

We describe the development of a multipoint nonparametric quantitative trait loci mapping method based on the Wilcoxon rank-sum test applicable to outbred half-sib pedigrees. The method has been evaluated ... [more ▼]

We describe the development of a multipoint nonparametric quantitative trait loci mapping method based on the Wilcoxon rank-sum test applicable to outbred half-sib pedigrees. The method has been evaluated on a simulated dataset and its efficiency compared with interval mapping by using regression. It was shown that the rank-based approach is slightly inferior to regression when the residual variance is homoscedastic normal; however, in three out of four other scenarios envisaged, i.e., residual variance heteroscedastic normal, homoscedastic skewed, and homoscedastic positively kurtosed, the latter outperforms the former one. Both methods were applied to a real data set analyzing the effect of bovine chromosome 6 on milk yield and composition by using a 125-cM map comprising 15 microsatellites and a granddaughter design counting 1158 Holstein-Friesian sires. [less ▲]

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See detailMapping quantitative trait loci controlling milk production by exploiting progeny testing
Georges, Michel ULg; Nielsen, D.; Mackinnon, M. et al

in Genetics (1995), 139

We have exploited "progeny testing" to map quantitative trait loci (QTL) underlying the genetic variation of milk production in a selected dairy cattle population. A total of 1,518 sires, with progeny ... [more ▼]

We have exploited "progeny testing" to map quantitative trait loci (QTL) underlying the genetic variation of milk production in a selected dairy cattle population. A total of 1,518 sires, with progeny tests based on the milking performances of > 150,000 daughters jointly, was genotyped for 159 autosomal microsatellites bracketing 1645 centimorgan or approximately two thirds of the bovine genome. Using a maximum likelihood multilocus linkage analysis accounting for variance heterogeneity of the phenotypes, we identified five chromosomes giving very strong evidence (LOD score > or = 3) for the presence of a QTL controlling milk production: chromosomes 1, 6, 9, 10 and 20. These findings demonstrate that loci with considerable effects on milk production are still segregating in highly selected populations and pave the way toward marker-assisted selection in dairy cattle breeding. [less ▲]

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See detailThe effects of selection on linkage analysis for quantitative traits
Mackinnon, M. J.; Georges, Michel ULg

in Genetics (1992), 132

The effects of within-sample selection on the outcome of analyses detecting linkage between genetic markers and quantitative traits were studied. It was found that selection by truncation for the trait of ... [more ▼]

The effects of within-sample selection on the outcome of analyses detecting linkage between genetic markers and quantitative traits were studied. It was found that selection by truncation for the trait of interest significantly reduces the differences between marker genotype means thus reducing the power to detect linked quantitative trait loci (QTL). The size of this reduction is a function of proportion selected, the magnitude of the QTL effect, recombination rate between the marker locus and the QTL, and the allele frequency of the QTL. Proportion selected was the most influential of these factors on bias, e.g., for an allele substitution effect of one standard deviation unit, selecting the top 80%, 50% or 20% of the population required 2,6 or 24 times the number of progeny, respectively, to offset the loss of power caused by this selection. The effect on power was approximately linear with respect to the size of gene effect, almost invariant to recombination rate, and a complex function of QTL allele frequency. It was concluded that experimental samples from animal populations which have been subjected to even minor amounts of selection will be inefficient in yielding information on linkage between markers and loci influencing the quantitative trait under selection. [less ▲]

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See detailModification of Chloroplast Gene Transmission in Somatic Fusion Products and Vegetative Zygotes of Chlamydomonas Reinhardi by 5-Fluorodeoxyuridine
Matagne, René-Fernand ULg; Hermesse, Marie-Paule

in Genetics (1981), 99(3-4), 371-381

Sexual crosses and somatic fusions were performed between complementing wall-less arg(-) mutant strains bearing chloroplast markers for resistance to antibiotics. The mode of chloroplast allele ... [more ▼]

Sexual crosses and somatic fusions were performed between complementing wall-less arg(-) mutant strains bearing chloroplast markers for resistance to antibiotics. The mode of chloroplast allele transmission was investigated in the diploid colonies developed from both vegetative zygotes and fusion products. Before mating or fusion, one or both of the parental strains were grown for 4 or 8 days on agar containing 5-fluorodeoxyuridine (FUdR, 0.1 to 1.0 mm), which selectively reduces the amount of chloroplast DNA in Chlamydomonas. When one parent was pregrown on FUdR, the frequency of vegetative zygotes transmitting chloroplast alleles of both parents (biparental or BP zygotes) decreased, the reduction being more drastic when the mt(-) parent was treated. Transmission was mainly uniparental maternal (UPm) or paternal (UPp) depending on whether the mt(-) or the mt(+) parent was pregrown for 8 days in the presence of 1.0 mm FUdR. Treatment of both parents led to a strong maternal transmission. In the experiments involving somatic fusion between parent 1 and parent 2 (same or opposite mt), the ratio UP(1)/UP(2), which was approximately equal to 1 in the control, decreased or increased according to whether the cells of parent 1 or 2 were pregrown on FUdR. In parallel, the frequency of BP fusion products always decreased. When both parental strains were treated with FUdR, the frequency of BP fusion products also decreased and the ratio UP(1)/UP(2) was roughly equal to 1. The effect of FUdR can be interpreted in terms of reduction of the input frequencies of parental chloroplast genomes at the time of gametic or somatic cell fusion, the bias in favor of the maternal parent being operational only in sexual crosses. [less ▲]

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