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PubMed2002

[Detection and analysis of QTL for resistance to the brown planthopper, Nilaparvata lugens (Stål), in rice (Oryza sativa L.), using backcross inbred lines].

A mapping population of 98 BC1F9 lines (backcross inbred lines: BILs), derived from a backcross of Nipponbare (japonica)/Kasalath (indica)//Nipponbare by the single-seed descent methods, was used to detect quantitative trait loci (QTL) for resistance to brown planthopper (BPH), Nilaparvata lugens (Stål). Seedbox Screening Technique (SST) was applied to evaluate the reactions of two parents and 98 BILs to BPH at the seedling stage, and the entries were graded on ratio of dead seedlings. A total of three QTL controlling BPH resistance were detected on chromosomes 2, 10 and 12, respectively. Individual QTL accounted for between 10.4% and 16.6% of the phenotypic variance, and the resistance of all the three QTL came from Kasalath, the moderate resistance parent. These QTL should be useful in breeding of varieties resistant to BPH in marker-assisted selection (MAS) program.

Chromosome Mapping↗
PubMed2003

QTL analysis of morphological traits in eggplant and implications for conservation of gene function during evolution of solanaceous species.

An interspecific F(2) population from a cross between cultivated eggplant, Solanum melongena, and its wild relative, S. linnaeanum, was analyzed for quantitative trait loci (QTL) affecting leaf, flower, fruit and plant traits. A total of 58 plants were genotyped for 207 restriction fragment length polymorphism (RFLP) markers and phenotyped for 18 characters. One to eight loci were detected for each trait with a total of 63 QTL identified. Overall, 46% of the QTL had allelic effects that were the reverse of those predicted from the parental phenotypes. Wild alleles that were agronomically superior to the cultivated alleles were identified for 42% of the QTL identified for flowering time, flower and fruit number, fruit set, calyx size and fruit glossiness. Comparison of the map positions of eggplant loci with those for similar traits in tomato, potato and pepper revealed that 12 of the QTL have putative orthologs in at least one of these other species and that putative orthology was most often observed between eggplant and tomato. Traits showing potential orthology were: leaf length, shape and lobing; days to flowering; number of flowers per inflorescence; plant height and apex, leaf and stem hairiness. The functionally conserved loci included a major leaf lobing QTL ( llob6.1) that is putatively orthologous to the potato leaf ( c) and/or Petroselinum ( Pts) mutants of tomato, two flowering time QTL ( dtf1.1, dtf2.1) that also have putative counterparts in tomato and four QTL for trichomes that have potential orthologs in tomato and potato. These results support the mounting evidence of conservation of gene function during the evolution of eggplant and its relatives from their last common ancestor and indicate that this conservation was not limited to domestication traits.

Chromosome Mapping↗
PubMed2002

Marker-assisted introgression of quantitative trait loci associated with plant regeneration ability in anther culture of Rice (Oryza sativa L.).

A marker-assisted selection (MAS) breeding program was used to improve the plant regenerability of indica rice. A significant quantitative trait loci (QTL) that is associated with the capacity for green plant regeneration in the anther culture of rice was mapped on chromosome 10 using recombinant inbred (RI) population from Milyang 23/Gihobyeo. The marker that was chosen to follow the QTL region was used in MAS. This marker co-segregated with the regeneration ability in F2 individuals that were derived from MGRI 079/IR 36. In order to clarify the relationship between this marker and plant regenerability, the backcross population was screened with a RFLP marker. The capacity of plant regeneration of the backcross population was clearly distinguished by the marker genotype. The development of near isogenic line (NILs) with high regenerability through MAS will save time, labor, and cost in indica rice breeding.

Biomarkers↗
PubMed2005

The Vrn-H2 locus is a major determinant of flowering time in a facultative x winter growth habit barley (Hordeum vulgare L.) mapping population.

With the aim of dissecting the genetic determinants of flowering time, vernalization response, and photoperiod sensitivity, we mapped the candidate genes for Vrn-H2 and Vrn-H1 in a facultative x winter barley mapping population and determined their relationships with flowering time and vernalization via QTL analysis. The Vrn-H2 candidate ZCCT-H genes were completely missing from the facultative parent and present in the winter barley parent. This gene was the major determinant of flowering time under long photoperiods in controlled environment experiments, irrespective of vernalization, and under spring-sown field experiments. It was the sole determinant of vernalization response, but the effect of the deletion was modulated by photoperiods when the vernalization requirement was fulfilled. There was no effect under short photoperiods. The Vrn-H1 candidate gene (HvBM5A) was mapped based on a microsatellite polymorphism we identified in the promoter of this gene. Otherwise, the HvBM5A alleles for the two parents were identical. Therefore, the significant flowering time QTL effect associated with this locus suggests tight linkage rather than pleiotropy. This QTL effect was smaller in magnitude than those associated with the Vrn-H2 locus and was significant in two-way interactions with Vrn-H2. The Vrn-H1 locus had no effect on vernalization response. Our results support the Vrn-H2/Vrn-H1 repressor/structural gene model for vernalization response in barley and suggest that photoperiod may also affect the Vrn genes or tightly linked loci.

Chromosome Mapping↗
PubMed2001

[Mapping genes for rice CMS-WA fertility restoration].

In a population consisting of 227 test-crosses of Zhenshan 97A x (Zhenshan 97B x Milyang 46) F6, a linkage map of 115 RFLP markers was constructed and employed to detect QTL for rice CMS-WA (wild abortive cytoplasmic male sterility) fertility restoration. One QTL having major effect, qRf-10, and 3 QTL having minor effects, qRf-1, qRf-7 and qRf-11, were detected. The four genes mainly acted additively with each other, but epistasis was also evident. Two minor QTL, qRf-1 and qRf-11, were significantly interacted with the major gene qRf-10. It was also found that interaction effects among minor QTL varied greatly depending on whether qRf-10 was present. Two other QTL, qSF-1 and qSF-7, were detected, which did not display any effects on fertility restoration. Instead, they showed effects for increasing SF when qRf-10 was present.

Chromosome Mapping↗
PubMed2003

Identification of quantitative trait loci for yield and yield components in an advanced backcross population derived from the Oryza sativa variety IR64 and the wild relative O. rufipogon.

A BC(2)F(2) population developed from an interspecific cross between Oryza sativa (cv IR64) and O. rufipogon (IRGC 105491) was used in an advanced backcross QTL analysis to identify and introduce agronomically useful genes from this wild relative into the cultivated gene pool. The objectives of this study were: (1) to identify putative yield and yield component QTLs that can be useful to improve the elite cultivar IR64; (2) to compare the QTLs within this study with previously reported QTLs in rice as the basis for identifying QTLs that are stable across different environments and genetic backgrounds; and (3) to compare the identified QTLs with previously reported QTLs from maize to examine the degree of QTL conservation across the grass family. Two hundred eighty-five families were evaluated in two field environments in Indonesia, with two replications each, for 12 agronomic traits. A total of 165 markers consisting of 131 SSRs and 34 RFLPs were used to construct the genetic linkage map. By employing interval mapping and composite interval mapping, 42 QTLs were identified. Despite its inferior performance, 33% of the QTL alleles originating from O. rufipogon had a beneficial effect for yield and yield components in the IR64 background. Twenty-two QTLs (53.4%) were located in similar regions as previously reported rice QTLs, suggesting the existence of stable QTLs across genetic backgrounds and environments. Twenty QTLs (47.6%) were exclusively detected in this study, uncovering potentially novel alleles from the wild, some of which might improve the performance of the tropical indica variety IR64. Additionally, several QTLs for plant height, grain weight, and flowering time detected in this study corresponded to homeologous regions in maize containing previously detected maize QTLs for these traits.

Base Sequence↗
PubMed2005

Quantitative trait locus analysis of aggressive behaviours in mice.

Quantitative trait locus (QTL) analysis is a forward genetic strategy (phenotype to gene) that enables an investigator to start with a phenotype of interest (e.g. aggressive behaviours), and then identify chromosomal regions (QTLs) and, ultimately, specific gene variants (alleles) within those regions, that influence quantitative variation in the phenotype. QTL analysis is an important complement to reverse genetic strategies (gene to phenotype), such as the generation of knockout and transgenic mice. Although a propensity for aggressive behaviours is partially heritable in mice and other mammals, very few aggression QTLs have been mapped. This slow progress is likely due, in part, to the complexity of aggressive behaviours as phenotypes, which are affected by many nongenetic (environmental and random) factors and gene-environment interactions. This paper reviews the general principles of QTL analysis, as well as the non-genetic factors that can confound aggression QTL studies. Some examples of successfully mapped intermale mouse aggression QTLs are presented, such as QTLs on chromosomes 10 and X. Strategies for fine mapping these loci are discussed, and candidate genes are considered. Finally, newly available mouse genetic resources that may facilitate QTL analysis of aggressive behaviours are suggested, such as consomic mouse strains.

Aggression↗
PubMed2004

Integration and modularity of quantitative trait locus effects on geometric shape in the mouse mandible.

The mouse mandible has long served as a model system for complex morphological structures. Here we use new methodology based on geometric morphometrics to test the hypothesis that the mandible consists of two main modules, the alveolar region and the ascending ramus, and that this modularity is reflected in the effects of quantitative trait loci (QTL). The shape of each mandible was analyzed by the positions of 16 morphological landmarks and these data were analyzed using Procrustes analysis. Interval mapping in the F(2) generation from intercrosses of the LG/J and SM/J strains revealed 33 QTL affecting mandible shape. The QTL effects corresponded to a variety of shape changes, but ordination or a parametric bootstrap test of clustering did not reveal any distinct groups of QTL that would affect primarily one module or the other. The correlations of landmark positions between the two modules tended to be lower than the correlations between arbitrary subsets of landmarks, indicating that the modules were relatively independent of each other and confirming the hypothesized location of the boundary between them. While these results are in agreement with the hypothesis of modularity, they also underscore that modularity is a question of the relative degrees to which QTL contribute to different traits, rather than a question of discrete sets of QTL contributing to discrete sets of traits.

Animals↗
PubMed2005

The main effects, epistatic effects and environmental interactions of QTLs on the cooking and eating quality of rice in a doubled-haploid line population.

Amylose content (AC), gel consistency (GC) and gelatinazation temperature (GT) are three important traits that influence the cooking and eating quality of rice. The objective of this study was to characterize the genetic components, including main-effect quantitative trait loci (QTLs), epistatic QTLs and QTL-by-environment interactions (QEs), that are involved in the control of these three traits. A population of doubled haploid (DH) lines derived from a cross between two indica varieties Zhenshan 97 and H94 was used, and data were collected from a field experiment conducted in two different environments. A genetic linkage map consisting of 218 simple sequence repeat (SSR) loci was constructed, and QTL analysis performed using QTLMAPPER 1.6: resolved the genetic components into main-effect QTLs, epistatic QTLs and QEs. The analysis detected a total of 12 main-effect QTLs for the three traits, with a QTL corresponding to the Wx locus showing a major effect on AC and GC, and a QTL corresponding to the Alk locus having a major effect on GT. Ten digenic interactions involving 19 loci were detected for the three traits, and six main-effect QTLs and two pairs of epistatic QTLs were involved in QEs. While the main-effect QTLs, especially the ones corresponding to known major loci, apparently played predominant roles in the genetic basis of the traits, under certain conditions epistatic effects and QEs also played important roles in controlling the traits. The implications of the findings for rice quality improvement are discussed.

Amylose↗
PubMed2004

Quantitative trait loci affecting life span in replicated populations of Drosophila melanogaster. II. Response to selection.

Three selection experiments were used to identify chromosome regions that contain QTL affecting late-life and early-life fitness in Drosophila melanogaster. The selection experiments were initiated by crossing pairs of inbred lines that had been derived from outbred laboratory populations that had different mean life spans. QTL regions were located by association with microsatellite markers that showed significant selection responses. Regions between recombination map positions 54 and 81 on chromosome 2, between 0 and 30 on chromosome 3, and near locations 49 and 81 on chromosome 3 had the strongest support as locations of life-span QTL. There was good general agreement between the life-span QTL regions that were identified by selection and those that were identified in a companion recombination mapping experiment that used the same fly stocks. Many marker loci responded in opposite directions to selection for late- and early-life fitness, indicating negative genetic correlations or trade-offs between those traits. Indirect evidence suggested that some negative genetic correlations were due to antagonistic pleiotropy.

Animals↗
PubMed2006

Short communication: quantitative trait loci affecting the somatic cell score on chromosomes 4 and 26 in Italian Holstein cattle.

This work aimed to confirm previously reported quantitative trait loci (QTL) affecting the somatic cell score (SCS) in dairy cattle on Bos taurus autosomes (BTA) 4 and 26. A granddaughter design with selective genotyping was implemented that included half-sib families from 12 male lines of Italian Holstein cattle. The animals were genotyped for 5 microsatellite markers each on regions of BTA 4 (average marker spacing 9.42 cM) and BTA 26 (average marker spacing 5.26 cM), previously reported by other authors as carrying QTL for somatic cell count. Quantitative trait loci analyses were performed using interval mapping by regressing sire breeding values for SCS onto genotype probabilities at 1-cM intervals along the 2 chromosome regions. Breeding values for SCS were estimated for the whole population using a test-day repeatability animal model. Results were not significant on a chromosome basis, but a possible QTL was found at BM4505 on BTA 26, confirming this region for further studies of QTL affecting SCS in the Italian Holstein population.

Animals↗
PubMed2000

Mapping of genes for cooking and eating qualities in Thai jasmine rice (KDML105).

Thai jasmine rice, KDML 105, is known as the best quality rice. It is known not only for its aroma but also for its good cooking and eating qualities. Amylose content (AC), gel consistency (GC) and gelatinization temperature (GT) are important traits determining rice quality. A population of recombinant inbred lines (RIL) derived from KDML105 x CT9993 cross was used to study the genetic control of AC, GC and GT traits. A total of 191 markers were used in the linkage map construction. The 1605.3 cM linkage map covering nearly the whole rice genome was used for QTL (define QTL) analysis. Four QTLs for AC were detected on chromosomes 3, 4, 6 and 7. These QTLs accounted for 80% of phenotypic variation explained (PVE) in AC. The presence of one major gene as well as several modifiers was responsible for the expression of the trait. Two QTLs on chromosome 6 and one on chromosome 7 were detected for GC, which accounts for 57% of PVE. A single gene of major effect along with modifier genes controls GC from this cross. The QTLs in the vicinity of waxy locus were major contributors in the expression of AC and GC. The finding that the position of QTLs for AC and GC were near each other may reflect tight linkage or pleiotropy. Three QTLs were detected, one on chromosome 2 and two on chromosome 6, which accounted for 67% of PVE in GT. Just like AC and GC, one major gene and modifier genes governed the variation in GT resulting from the KDML105 x CT9993 cross. Breeding for cooking and eating qualities will largely rely on the preferences of the end users.

Amylose↗
PubMed2000

Identification of heading date quantitative trait locus Hd6 and characterization of its epistatic interactions with Hd2 in rice using advanced backcross progeny.

A backcrossed population (BC(4)F(2)) derived from a cross between a japonica rice variety, Nipponbare, as the recurrent parent and an indica rice variety, Kasalath, as the donor parent showed a long-range variation in days to heading. Quantitative trait loci (QTL) analysis revealed that two QTL, one on chromosome 3, designated Hd6, and another on chromosome 2, designated Hd7, were involved in this variation; and Hd6 was precisely mapped as a single Mendelian factor by using progeny testing (BC(4)F(3)). The nearly isogenic line with QTL (QTL-NIL) that carries the chromosomal segment from Kasalath for the Hd6 region in Nipponbare's genetic background was developed by marker-assisted selection. In a day-length treatment test, the QTL-NIL for Hd6 prominently increased days to heading under a 13.5-hr day length compared with the recurrent parent, Nipponbare, suggesting that Hd6 controls photoperiod sensitivity. QTL analysis of the F(2) population derived from a cross between the QTL-NILs revealed existence of an epistatic interaction between Hd2, which is one of the photoperiod sensitivity genes detected in a previous analysis, and Hd6. The day-length treatment tests of these QTL-NILs, including the line introgressing both Hd2 and Hd6, also indicated an epistatic interaction for photoperiod sensitivity between them.

Chromosome Mapping↗
PubMed2005

Pnlip encoding pancreatic lipase is possible candidate for obesity QTL in the OLETF rat.

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat exhibits polygenic obesity, and one of quantitative trait loci (QTLs) responsible for a susceptibility to obesity in the OLETF, Nidd6/of, has been mapped to the approximately 10-cM genomic region between D1Rat166 and D1Rat90 on chromosome 1 in (OLETF x normal) F2 intercross. In this study, we have attempted to identify the causal gene for the Nidd6/of QTL. A Nidd6/of congenic strain, constructed by introgressing the OLETF allele on the mapped Nidd6/of region in the normal F344 rat strain, confirmed the existence of the Nidd6/of as obesity QTL. The Nidd6/of region was refined to a approximately 2.3-cM genomic region between D1Rat225 and D1Rat90, using informative recombinants selected from (Nidd6/of congenic x F344) F1 x Nidd6/of congenic backcross progenies. Among 46 genes located within the approximately 2.3-cM region, pancreatic lipase gene, Pnlip, was regarded as the most prominent and physiologically relevant positional candidate for the Nidd6/of QTL. We found that Pnlip possesses an OLETF allele-specific increase of mRNA levels in the pancreas, and that the OLETF allele is longer in variable number of tandem repeat (VNTR) within the 5'-flanking region than normal alleles. We further showed that the Nidd6/of QTL completely cosegregates with Pnlip VNTR in the informative recombinants from (Nidd6/of congenic x F344) F1 x Nidd6/of congenic backcross progenies. These results suggest that Pnlip is possible candidate for the Nidd6/of QTL.

Animals↗
PubMed1999

Natural allelic variation identifies new genes in the Arabidopsis circadian system.

We have analysed the circadian rhythm of Arabidopsis thaliana leaf movements in the accession Cvi from the Cape Verde Islands, and in the commonly used laboratory strains Columbia (Col) and Landsberg (erecta) (Ler), which originated in Northern Europe. The parental lines have similar rhythmic periods, but the progeny of crosses among them reveal extensive variation for this trait. An analysis of 48 Ler/Cvi recombinant inbred lines (RILs) and a further 30 Ler/Col RILs allowed us to locate four putative quantitative trait loci (QTLs) that control the period of the circadian clock. Near-isogenic lines (NILs) that contain a QTL in a small, defined chromo- somal region allowed us to confirm the phenotypic effect and to map the positions of three period QTLs, designated ESPRESSO, NON TROPPO and RALENTANDO. Quantitative trait loci at the locations of RALENTANDO and of a fourth QTL, ANDANTE, were identified in both Ler/Cvi and Ler/Col RIL populations. Some QTLs for circadian period are closely linked to loci that control flowering time, including FLC. We show that flc mutations shorten the circadian period such that the known allelic variation in the MADS-box gene FLC can account for the ANDANTE QTL. The QTLs ESPRESSO and RALENTANDO identify new genes that regulate the Arabidopsis circadian system in nature, one of which may be the flowering-time gene GIGANTEA.

Alleles↗
PubMed2004

Detection and mapping of quantitative trait loci that determine responsiveness of mice to nitrous oxide antinociception.

Exposure to 70% N(2)O evokes a robust antinociceptive effect in C57BL/6 (B6) but not in DBA/2 (D2) inbred mice. This study was conducted to identify quantitative trait loci (QTL) in the mouse genome that might determine responsiveness to N(2)O. Offspring from the F(2) generation bred from B6 and D2 progenitors exhibited a broad range of responsiveness to N(2)O antinociception as determined by the acetic acid-induced abdominal constriction test. QTL analysis was then used to dissect this continuous trait distribution into component loci, and to map them to broad chromosomal regions. To this end, 24 spleens were collected from each of the following four groups: male and female F(2) mice responding to 70% N(2)O in oxygen with 100% response (high-responders); and male and female F(2) mice responding with 0% response (low-responders). Genomic DNA was extracted from the spleens and genotyped with simple sequence length polymorphism MapPairs markers. Findings were combined with findings from the earlier QTL analysis from BXD recombinant inbred mice [Brain Res 725 (1996) 23]. Combined results revealed two significant QTL that influence responsiveness to nitrous oxide on proximal chromosome 2 and distal chromosome 5, and one suggestive QTL on midchromosome 18. The chromosome 2 QTL was evident only in males. A significant interaction was found between a locus on chromosome 6 and another on chromosome 13 with a substantial effect on N(2)O antinociception.

Animals↗
PubMed2005

[QTLs mapping and genetic analysis of tiller angle in rice (Oryza sativa L.)].

Tiller angle is one of the most important morphological characters that has a significant effect on the formation of rice high-yield population. The tiller angles were measured in a japonica/indica RIL population with 71 lines and a genome-wide chromosome segment substitution line (CSSL) population with 65 lines at two experimental sites. A transgressive segregation was observed in both populations. QTL analysis of tiller angle was conducted based on the saturated RFLP marker linkage map and the CSSL graphical genetype. Five main-effect QTLs and three pairs of epstatic loci were detected in the RIL population. A main QTL, qTA-9, located on chromosome 9 at XNpb108 - C506, was identified at both experiment sites. The positive allele TA-9(I) on qTA-9 was contributed by indica rice IR24 with 28.6% average contribution to variance. Meanwhile, an analysis of CSSL graphical genetypes also showed that there was a positive allele on the IR24 chromosome substitution segment delimited by RFLP marker C609 and C506 with approximate 15 cM interval, which proved the existence of qTA-9. The TA-9(I) could increase tiller angle by about 15 degrees in japonica Asominori background under the two environments. The measurement of the F1 from the cross between background parent and CSSL AIS68 with TA-9(I) and the analysis of F2 population indicated that the TA-9(I) was an incomplete dominant gene. Genetype x environment interaction(G xE) was not widely present except a pair of epistatic loci with 5.32% contribution to variance of tiller angles and a relatively small additive effect. The combining action of the additive effect of the genes from both parents and the two-loci epistasis-effect may be responsible for the transgressive segregation of tiller angle in rice population. The value and approach of application of TA-9(I) in hybrid rice breeding program were discussed.

Chromosome Mapping↗
PubMed1995

A random model approach to interval mapping of quantitative trait loci.

Mapping quantitative trait loci in outbred populations is important because many populations of organisms are noninbred. Unfortunately, information about the genetic architecture of the trait may not be available in outbred populations. Thus, the allelic effects of genes can not be estimated with ease. In addition, under linkage equilibrium, marker genotypes provide no information about the genotype of a QTL (our terminology for a single quantitative trait locus is QTL while multiple loci are referred to as QTLs). To circumvent this problem, an interval mapping procedure based on a random model approach is described. Under a random model, instead of estimating the effects, segregating variances of QTLs are estimated by a maximum likelihood method. Estimation of the variance component of a QTL depends on the proportion of genes identical-by-descent (IBD) shared by relatives at the locus, which is predicted by the IBD of two markers flanking the QTL. The marker IBD shared by two relatives are inferred from the observed marker genotypes. The procedure offers an advantage over the regression interval mapping in terms of high power and small estimation errors and provides flexibility for large sibships, irregular pedigree relationships and incorporation of common environmental and fixed effects.

Alleles↗