Construction of High-Density Genetic Linkage Maps and Mapping of Growth-Related Quantitative Trail Loci in the Japanese Flounder (Paralichthys olivaceus)

High-density genetic linkage maps were constructed for the Japanese flounder (Paralichthys olivaceus). A total of 1624 microsatellite markers were polymorphic in the reference family. Linkage analysis using JoinMap 4.0 resulted in the mapping of 1487 markers to 24 linkage groups, a result which was consistent with the 24 chromosomes seen in chromosome spreads. The female map was composed of 1257 markers, covering a total of 1663.8 cM with an average interval 1.35 cM between markers. The male map consisted of 1224 markers, spanning 1726.5 cM, with an average interval of 1.44 cM. The genome length in the Japanese flounder was estimated to be 1730.3 cM for the females and 1798.0 cM for the males, a coverage of 96.2% for the female and 96.0% for the male map. The mean recombination at common intervals throughout the genome revealed a slight difference between sexes, i.e. 1.07 times higher in the male than female. High-density genetic linkage maps are very useful for marker-assisted selection (MAS) programs for economically valuable traits in this species and for further evolutionary studies in flatfish and vertebrate species. Furthermore, four quantiative trait loci (QTL) associated with growth traits were mapped on the genetic map. One QTL was identified for body weight on LG 14 f, which explained 14.85% of the total variation of the body weight. Three QTL were identified for body width on LG14f and LG14m, accounting for 16.75%, 13.62% and 13.65% of the total variation in body width, respectively. The additive effects were evident as negative values. There were four QTL for growth traits clustered on LG14, which should prove to be very useful for improving growth traits using molecular MAS.     

Quantitative trait loci for body growth and sex determination in the hermaphrodite teleost fish Sparus aurata L.

Gilthead sea bream (Sparus aurata L.) is an important marine fish in Mediterranean aquaculture. Sex determination by age and/or body weight is a critical life‐history trait, the genetic basis for which is largely unknown in this sequential hermaphrodite species. Herein, we performed a partial genome scan to map quantitative trait loci (QTL) affecting body weight and sex using 74 informative microsatellite markers from 10 paternal half‐sib families to construct nine linkage groups (LG). In total, four growth‐related QTL (two chromosome‐wide and two genome‐wide) and six QTL related to sex determination (three pairs in three different LGs) were detected (two chromosome‐wide and one genome‐wide). The proportion of phenotypic variation explained by the body‐weight QTL ranged from 9.3% to 17.2%, showing their potential for use in marker‐assisted selection. The results obtained offer solid ground to investigate the structure and function of the genomic regions involved in the mechanisms of sex reversal.     

Characterization of variation and quantitative trait loci related to terpenoid indole alkaloid yield in a recombinant inbred line mapping population of <Emphasis Type="Italic">Catharanthus roseus</Emphasis>

Improved Catharanthus roseus cultivars are required for high yields of vinblastine, vindoline and catharanthine and/or serpentine and ajmalicine, the pharmaceutical terpenoid indole alkaloids. An approach to derive them is to map QTL for terpenoid indole alkaloids yields, identify DNA markers tightly linked to the QTL and apply marker assisted selection. Towards the end, 197 recombinant inbred lines from a cross were grown over two seasons to characterize variability for seven biomass and 23 terpenoid indole alkaloids content-traits and yield-traits. The recombinant inbred lines were genotyped for 178 DNA markers which formed a framework genetic map of eight linkage groups (LG), spanning 1786.5 cM, with 10.0 cM average intermarker distance. Estimates of correlations between traits allowed selection of seven relatively more important traits for terpenoid indole alkaloids yields. QTL analysis was performed on them using single marker (regression) analysis, simple interval mapping and composite interval mapping procedures. A total of 20 QTL were detected on five of eight LG, 10 for five traits on LG1, five for four traits on LG2, three for one trait on LG3 and one each for different traits on LG three and four. QTL for the same or different traits were found clustered on three LG. Co-location of two QTL for biomass traits was in accord of correlation between them. The QTL were validated for use in marker assisted selection by the recombinant inbred line which transgressively expressed 16 traits contributory to the yield vinblastine, vindoline and catharanthine from leaves and roots that possessed favourable alleles of 13 relevant QTL.     

Mapping quantitative trait loci affecting chicken body size traits via genome scanning

Body size traits reflect the condition of body development, are always mentioned when a breed is described, and are also targets in breeding programmes. In chicken, there are several reports focused on body size traits, such as shank length, tibia length or bone traits. However, no study was carried out on chest width (CW), chest depth (CD), body slope length (BL) and head width (HW) traits. In this study, genome scans were conducted on an F₂ resource population (238 F₂ individuals from 15 full‐sib families derived from an intercross of the White Plymouth Rock with the Silkies Fowl) to identify quantitative trait loci (QTL) associated with CW, CD, BL and HW from 7 to 12 weeks of age. In total, 21 significant or suggestive QTL were found that affected four body size traits. Four QTL reached 1% genome‐wide significance level: at 297 cM on GGA3 (associated with CW at 9 weeks of age), between 155 and 184 cM on GGA1 (affecting BL traits at 9 and 10 weeks of age), at 22 cM on GGA2 (related with BL traits at 12 weeks of age) and at 36 cM on GGA1 (for HW trait at 8 weeks of age).     

QTL Mapping for Frond Length and Width in Laminaria japonica Aresch (Laminarales, Phaeophyta) Using AFLP and SSR Markers

In Laminaria japonica Aresch breeding practice, two quantitative traits, frond length (FL) and frond width (FW), are the most important phenotypic selection index. In order to increase the breeding efficiency by integrating phenotypic selection and marker-assisted selection, the first set of QTL controlling the two traits were determined in F₂ family using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers. Two prominent L. japonicas inbred lines, one with “broad and thin blade” characteristics and another with “long and narrow blade” characteristics, were applied in the hybridization to yield the F₂ mapping population with 92 individuals. A total of 287 AFLP markers and 11 SSR markers were used to construct a L. japonica genetic map. The yielded map was consisted of 28 linkage groups (LG) named LG1 to LG28, spanning 1,811.1 cM with an average interval of 6.7 cM and covering the 82.8% of the estimated genome 2,186.7 cM. While three genome-wide significant QTL were detected on LG1 (two QTL) and LG4 for “FL,” explaining in total 42.36% of the phenotypic variance, two QTL were identified on LG3 and LG5 for the trait “FW,” accounting for the total of 36.39% of the phenotypic variance. The gene action of these QTL was additive and partially dominant. The yielded linkage map and the detected QTL can provide a tool for further genetic analysis of two traits and be potential for maker-assisted selection in L. japonica breeding.     

Genome‐scan analysis for genetic mapping of quantitative trait loci underlying birth weight and onset of puberty in doe kids (Capra hircus)

The objective of this study was to locate quantitative trait loci (QTL) causing variation in birth weight and age of puberty of doe kids in a population of Rayini cashmere goats. Four hundred and thirty kids from five half‐sib families were genotyped for 116 microsatellite markers located on the caprine autosomes. The traits recorded were birth weight of the male and female kids, body weight at puberty, average daily gain from birth to age of puberty and age at puberty of the doe kids. QTL analysis was conducted using the least squares interval mapping approach. Linkage analysis indicated significant QTL for birth weight on Capra hircus chromosomes (CHI) 4, 5, 6, 18 and 21. Five QTL located on CHI 5, 14 and 29 were associated with age at puberty. Across‐family analysis revealed evidence for overlapping QTL affecting birth weight (78 cM), body weight at puberty (72 cM), average daily gain from birth to age of puberty (72 cM) and age at puberty (76 cM) on CHI 5 and overlapping QTL controlling body weight at puberty and age at puberty on CHI 14 at 18–19 cM. The proportion of the phenotypic variance explained by the detected QTL ranged between 7.9% and 14.4%. Confirming some of the previously reported results for birth weight and growth QTL in goats, this study identified more QTL for these traits and is the first report of QTL for onset of puberty in doe kids.     

Pleiotropic patterns of quantitative trait loci for 70 murine skeletal traits

Quantitative trait locus (QTL) studies of a skeletal trait or a few related skeletal components are becoming commonplace, but as yet there has been no investigation of pleiotropic patterns throughout the skeleton. We present a comprehensive survey of pleiotropic patterns affecting mouse skeletal morphology in an intercross of LG/J and SM/J inbred strains (N = 1040), using QTL analysis on 70 skeletal traits. We identify 798 single-trait QTL, coalescing to 105 loci that affect on average 7-8 traits each. The number of traits affected per locus ranges from only 1 trait to 30 traits. Individual traits average 11 QTL each, ranging from 4 to 20. Skeletal traits are affected by many, small-effect loci. Significant additive genotypic values average 0.23 standard deviation (SD) units. Fifty percent of loci show codominance with heterozygotes having intermediate phenotypic values. When dominance does occur, the LG/J allele tends to be dominant to the SM/J allele (30% vs. 8%). Over- and underdominance are relatively rare (12%). Approximately one-fifth of QTL are sex specific, including many for pelvic traits. Evaluating the pleiotropic relationships of skeletal traits is important in understanding the role of genetic variation in the growth and development of the skeleton.     

Linkage analysis and identification of quantitative trait loci associated with freeze tolerance and turf quality traits in St. Augustinegrass

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is a warm-season turfgrass commonly grown in the southern USA. In this study, the first linkage map for all nine haploid chromosomes of the species was constructed for cultivar ‘Raleigh’ and cultivar ‘Seville’ using a pseudo-F₂ mapping strategy. A total of 160 simple sequence repeat markers were mapped to nine linkage groups (LGs) covering a total distance of 1176.24 cM. To demonstrate the usefulness of the map, quantitative trait loci (QTL) were mapped controlling field winter survival, laboratory-based freeze tolerance, and turf quality traits. Multiple genomic regions associated with these traits were identified. Moreover, overlapping QTL were found for winterkill and spring green up on LG 3 (99.21 cM); turf quality, turf density, and leaf texture on LG 3 (68.57–69.50 cM); and surviving green tissue and regrowth on LGs 1 (38.31 cM), 3 (77.70 cM), 6 (49.51 cM), and 9 (34.20 cM). Additional regions, where QTL identified in both field and laboratory-based/controlled environment freeze testing co-located, provided strong support that these regions are good candidates for true gene locations. These results present the first complete linkage map produced for St. Augustinegrass, providing a template for further genetic mapping. Additionally, markers linked to the QTL identified may be useful to breeders for transferring these traits into new breeding lines and cultivars.     

A Consensus Microsatellite-Based Linkage Map for the Hermaphroditic Bay Scallop (Argopecten irradians) and Its Application in Size-Related QTL Analysis

Bay scallop (Argopecten irradians) is one of the most economically important aquaculture species in China. In this study, we constructed a consensus microsatellite-based genetic linkage map with a mapping panel containing two hybrid backcross-like families involving two subspecies of bay scallop, A. i. irradians and A. i. concentricus. One hundred sixty-one microsatellite and one phenotypic (shell color) markers were mapped to 16 linkage groups (LGs), which corresponds to the haploid chromosome number of bay scallop. The sex-specific map was 779.2 cM and 781.6 cM long in female and male, respectively, whereas the sex-averaged map spanned 849.3 cM. The average resolution of integrated map was 5.9 cM/locus and the estimated coverage was 81.3%. The proportion of distorted markers occurred more in the hybrid parents, suggesting that the segregation distortion was possibly resulted from heterospecific interaction between genomes of two subspecies of bay scallop. The overall female-to-male recombination rate was 1.13∶1 across all linked markers in common to both parents, and considerable differences in recombination also existed among different parents in both families. Four size-related traits, including shell length (SL), shell height (SH), shell width (SW) and total weight (TW) were measured for quantitative trait loci (QTL) analysis. Three significant and six suggestive QTL were detected on five LGs. Among the three significant QTL, two (qSW-10 and qTW-10, controlling SW and TW, respectively) were mapped on the same region near marker AiAD121 on LG10 and explained 20.5% and 27.7% of the phenotypic variance, while the third (qSH-7, controlling SH) was located on LG7 and accounted for 15.8% of the phenotypic variance. Six suggestive QTL were detected on four different LGs. The linkage map and size-related QTL obtained in this study may facilitate marker-assisted selection (MAS) in bay scallop.     

Identification of novel QTL for black tea quality traits and drought tolerance in tea plants (<Emphasis Type="Italic">Camellia sinensis</Emphasis>)

Tea (Camellia sinensis) contains polyphenols and caffeine which have been found to be of popular interest in tea quality. Tea production relies on well-distributed rainfall which influence tea quality. Phenotypic data for two segregating tea populations TRFK St 504 and TRFK St 524 were collected and used to identify the quantitative trait loci (QTL) influencing tea biochemical and drought stress traits based on a consensus genetic map constructed using the DArTseq platform. The populations comprised 261 F₁ clonal progeny. The map consisted of 15 linkage groups which corresponds to chromosome haploid number of tea plant (2n?=?2×?=?30) and spanned 1260.1 cM with a mean interval of 1.1 cM between markers. A total of 16 phenotypic traits were assessed in the two populations. Both interval and multiple QTL mapping revealed a total of 47 putative QTL in the 15 LGs associated with tea quality and percent relative water content at a significant genome-wide threshold of 5%. In total, six caffeine QTL, 25 catechins QTL, three theaflavins QTL, nine QTL for tea taster score, and three QTL for percent relative water contents were detected. Out of these 47 QTL, 19 QTL were identified for ten traits in three main regions on LG01, LG02, LG04, LG12, LG13, and LG14. The QTL associated with caffeine, individual catechins, and theaflavins were clustered mostly in LG02 and LG04 but in different regions on the map. The explained variance by each QTL in the population ranged from 5.5 to 56.6%, with an average of 9.9%. Identification of QTL that are tightly linked to markers associated with black tea quality coupled with UPLC assay may greatly accelerate development of novel tea cultivars owing to its amenability at seedling stage. In addition, validated molecular markers will contribute greatly to adoption of marker-assisted selection (MAS) for drought tolerance and tea quality improvement.     

Quantitative trait loci for magnitude of the plasma cortisol response to confinement in rainbow trout

Better understanding of the mechanisms underlying interindividual variation in stress responses and their links with production traits is a key issue for sustainable animal breeding. In this study, we searched for quantitative trait loci (QTL) controlling the magnitude of the plasma cortisol stress response and compared them to body size traits in five F2 full‐sib families issued from two rainbow trout lines divergently selected for high or low post‐confinement plasma cortisol level. Approximately 1000 F2 individuals were individually tagged and exposed to two successive acute confinement challenges (1 month interval). Post‐stress plasma cortisol concentrations were determined for each fish. A medium density genome scan was carried out (268 markers, overall marker spacing less than 10 cM). QTL detection was performed using qtlmap software, based on an interval mapping method ( http://www.inra.fr/qtlmap ). Overall, QTL of medium individual effects on cortisol responsiveness (<10% of phenotypic variance) were detected on 18 chromosomes, strongly supporting the hypothesis that control of the trait is polygenic. Although a core array of QTL controlled cortisol concentrations at both challenges, several QTL seemed challenge specific, suggesting that responses to the first and to a subsequent exposure to the confinement stressor are distinct traits sharing only part of their genetic control. Chromosomal location of the steroidogenic acute regulatory protein (STAR) makes it a good potential candidate gene for one of the QTL. Finally, comparison of body size traits QTL (weight, length and body conformation) with cortisol‐associated QTL did not support evidence for negative genetic relationships between the two types of traits.     

A genome scan for quantitative trait loci influencing carcass,post‐natal growth and reproductive traits in commercial Angus cattle

To gain insight into the number of loci of large effect that underlie variation in cattle, a quantitative trait locus (QTL) scan for 14 economically important traits was performed in two commercial Angus populations using 390 microsatellites, 11 single nucleotide polymorphisms (SNPs) and one duplication loci. The first population comprised 1769 registered Angus bulls born between 1955 and 2003, with Expected Progeny Differences computed by the American Angus Association. The second comprised 38 half‐sib families containing 1622 steers with six post‐natal growth and carcass phenotypes. Linkage analysis was performed by half‐sib least squares regression with gridqtl or Bayesian Markov chain Monte Carlo analysis of complex pedigrees with loki . Of the 673 detected QTL, only 118 have previously been reported, reflecting both the conservative approach to QTL reporting in the literature, and the more liberal approach taken in this study. From 33 to 71% of the genetic variance and 35 to 56% of the phenotypic variance in each trait was explained by the detected QTL. To analyse the effects of 11 SNPs and one duplication locus within candidate genes on each trait, a single marker analysis was performed by fitting an additive allele substitution model in both mapping populations. There were 53 associations detected between the SNP/duplication loci and traits with ?log₁₀P_nominal≥ 4.0, where each association explained 0.92% to 4.4% of the genetic variance and 0.01% to 1.86% of the phenotypic variance. Of these associations, only six SNP/duplication loci were located within 8 cM of a QTL peak for the trait, with two being located at the QTL peak: SST_DG156121:c.362A>G for ribeye muscle area and TG_X05380:c.422C>T for calving ease. Strong associations between several SNP/duplication loci and trait variation were obtained in the absence of any detected linked QTL. However, we reject the causality of several commercialized DNA tests, including an association between TG_X05380:c.422C>T and marbling in Angus cattle.     

Quantitative trait loci associated with constitutive traits control water use in pearl millet [Pennisetum glaucum (L.) R. Br.]

There is substantial genetic variation for drought adaption in pearl millet in terms of traits controlling plant water use. It is important to understand genomic regions responsible for these traits. Here, F₇ recombinant inbred lines were used to identify quantitative trait loci (QTL) and allelic interactions for traits affecting plant water use, and their relevance is discussed for crop productivity in water‐limited environments. Four QTL contributed to increased transpiration rate under high vapour pressure deficit (VPD) conditions, all with alleles from drought‐sensitive parent ICMB 841. Of these four QTL, a major QTL (35.7%) was mapped on linkage group (LG) 6. The alleles for 863B at this QTL decreased transpiration rate and this QTL co‐mapped to a previously detected LG 6 QTL, with alleles from 863B for grain weight and panicle harvest index across severe terminal drought stress environments. This provided additional support for a link between water saving from a lower transpiration rate under high VPD and drought tolerance. 863B alleles in this same genomic region also increased shoot weight, leaf area and total transpiration under well‐watered conditions. One unexpected outcome was reduced transpiration under high VPD (15%) from the interaction of two alleles for high VPD transpiration (LG 6 (B), 40.7) and specific leaf mass and biomass (LG 7 (A), 35.3), (A, allele from ICMB 841, B, allele from 863B, marker position). The LG 6 QTL appears to combine alleles for growth potential, beneficial for non‐stress conditions, and for saving water under high evaporative demand, beneficial under stressful conditions. Mapping QTL for water‐use traits, and assessing their interactions offers considerable potential for improving pearl millet adaptation to specific stress conditions through physiology‐informed marker‐assisted selection.     

Construction of microsatellite-based linkage maps and identification of size-related quantitative trait loci for Zhikong scallop (Chlamys farreri)

We constructed the microsatellite-based linkage maps using 318 markers typed in two F₁ outbred families of Zhikong scallop ( Chlamys farreri ). The results showed an extremely high proportion (56.2%) of non-amplifying null alleles and a high ratio (30%) of segregation distortion. By aligning different individual-based linkage maps, 19 linkage groups were identified, which are consistent with the haploid chromosome number of Zhikong scallop. The integrated linkage map contains 154 markers covering 1561.8 cM with an average intermarker spacing of 12.3 cM and 77.0% of genome coverage. We found that the heterogeneity in recombination rate was not determined by sexes but by different individuals on 18 linkage regions. The phenotypic marker of general shell colour was placed on LG4, which was flanked by microsatellite markers CFLD064 and CFBD055 . Four size-related traits including shell length (SL), shell width (SW), shell height (SH) and gross weight (GW) were analysed to identify the putative quantitative trait loci (QTL). Under the half-sib model, using dam as common parent, three, two, two and one QTL affecting SL, SW, SH and GW exceeded the genome-wide thresholds respectively. While using sir as common parent, a larger number of QTL were detected for these four traits: four, five, three and two for SL, SW, SH and GW respectively. The single QTL explained 3.7–19.2% of the phenotypic variation. The linkage map and the QTL associated with economic traits will provide useful information for marker-assisted selection of Zhikong scallop.     

Methods for the detection of multiple linked QTL applied to a mixture of full and half sib families

A new multiple trait strategy based on discriminant analysis was studied for efficient detection of linked QTL in outbred sib families, in comparison with a multivariate likelihood technique. The discriminant analysis technique describes the segregation of a linear combination of the traits in a univariate likelihood. This combination is calculated for each pair of positions depending on the inheritance of the pairs of QTL haplotypes in the progeny. The gains in power and accuracy for position estimations of multiple trait methods in grid searches were evaluated in reference to single trait detections of linked QTL. The methods were applied to simulated designs with two correlated traits submitted to various effects from the linked QTL. Multiple trait strategies were generally more powerful and accurate than the single trait technique. Linked QTL were distinguished when they were separated enough to identify informative recombinations: at least two genetic markers and 25 cM between the QTL under the simulated conditions. Except in a particular case, discriminant analysis was at least as powerful as the multivariate technique and its implementation was five times faster. Combining the advantages from both methodologies, we finally propose a complete strategy for rapid and efficient systematic multivariate detections in outbred populations.     

Within‐population polymorphism of sex‐determination systems in the common frog (Rana temporaria)

In sharp contrast with birds and mammals, the sex chromosomes of ectothermic vertebrates are often undifferentiated, for reasons that remain debated. A linkage map was recently published for Rana temporaria (Linnaeus, 1758) from Fennoscandia (Eastern European lineage), with a proposed sex‐determining role for linkage group 2 (LG2). We analysed linkage patterns in lowland and highland populations from Switzerland (Western European lineage), with special focus on LG2. Sibship analyses showed large differences from the Fennoscandian map in terms of recombination rates and loci order, pointing to large‐scale inversions or translocations. All linkage groups displayed extreme heterochiasmy (total map length was 12.2 cM in males, versus 869.8 cM in females). Sex determination was polymorphic within populations: a majority of families (with equal sex ratios) showed a strong correlation between offspring phenotypic sex and LG2 paternal haplotypes, whereas other families (some of which with female‐biased sex ratios) did not show any correlation. The factors determining sex in the latter could not be identified. This coexistence of several sex‐determination systems should induce frequent recombination of X and Y haplotypes, even in the absence of male recombination. Accordingly, we found no sex differences in allelic frequencies on LG2 markers among wild‐caught male and female adults, except in one high‐altitude population, where nonrecombinant Y haplotypes suggest sex to be entirely determined by LG2. Multifactorial sex determination certainly contributes to the lack of sex‐chromosome differentiation in amphibians.     

Genetic mapping of EST-derived simple sequence repeats (EST-SSRs) to identify QTL for leaf morphological characters in a Quercus robur full-sib family

The availability of genomic resources such as expressed sequence tag-derived simple sequence repeat (EST-SSR) markers in adaptive genes with high transferability across related species allows the construction of genetic maps and the comparison of genome structure and quantitative trait loci (QTL) positions. In the present study, genetic linkage maps were constructed for both parents of a Quercus robur × Q. robur ssp. slavonica full-sib pedigree. A total of 182 markers (61 AFLPs, 23 nuclear SSRs, 98 EST-SSRs) and 172 markers (49 AFLPs, 21 nSSRs, 101 EST-SSRs, 1 isozyme) were mapped on the female and male linkage maps, respectively. The total map length and average marker spacing were 1,038 and 5.7 cM for the female map and 998.5 and 5.8 cM for the male map. A total of 68 nuclear SSRs and EST-SSRs segregating in both parents allowed to define homologous linkage groups (LG) between both parental maps. QTL for leaf morphological traits were mapped on all 12 LG at a chromosome-wide level and on 6 LG at a genome-wide level. The phenotypic effects explained by each single QTL ranged from 4.0 % for leaf area to 15.8 % for the number of intercalary veins. QTL clusters for leaf characters that discriminate between Q. robur and Quercus petraea were mapped reproducibly on three LG, and some putative candidate genes among potentially many others were identified on LG3 and LG5. Genetic linkage maps based on EST-SSRs can be valuable tools for the identification of genes involved in adaptive trait variation and for comparative mapping.     

Quantitative trait loci affecting morphology traits in gilthead seabream (Sparus aurata L.)

We report a quantitative trait loci (QTL) mapping study on 18 morphometric characters in gilthead seabream based on a total of 74 informative microsatellite markers genotyped in 409 offspring coming from 10 paternal half‐sib families. Statistical analysis was carried out using a linear regression approach, and various suggestive and significant morphology QTL were detected in three (9, 21 and 25) of nine linkage groups examined. Fitting body weight as a covariate reduced the significance of some QTL but revealed three new QTL in other linkage groups (LG6 and LG10). Current results combined with those obtained from previous studies underline highly significant loci affecting overall growth and morphology in S. aurata.     

Quantitative trait locus (QTL) analysis of wood quality traits in <Emphasis Type="Italic">Eucalyptus nitens</Emphasis>

To identify the chromosomal regions affecting wood quality traits, we conducted a genome-wide quantitative trait locus (QTL) analysis of wood quality traits in Eucalyptus nitens. This information is important to exploit the full potential of the impending Eucalyptus genome sequence. A three generational mapping population consisting of 296 progeny trees was used to identify QTL associated with several wood quality traits in E. nitens. Thirty-six QTL positions for cellulose content, pulp yield, lignin content, density, and microfibril angle (MFA) were identified across different linkage groups. On linkage groups (LG)2 and 8, cellulose QTL cluster with pulp yield and extractives QTL while on LG4 and 10 cellulose and pulp yield QTLs cluster together. Similarly, on LG4, 5, and 6 QTL for lignin traits were clustered together. At two positions, QTL for MFA, a physical trait related to wood stiffness, were clustered with QTL for lignin traits. Several cell wall candidate genes were co-located to QTL positions affecting different traits. Comparative QTL analysis with Eucalyptus globulus revealed two common QTL regions for cellulose and pulp yield. The QTL positions identified in this study provide a resource for identifying wood quality genes using the impending Eucalyptus genome sequence. Candidate genes identified in this study through co-location to QTL regions may be useful in association studies.     

海岛棉产量和早熟性相关性状的QTLs定位

对海岛棉产量和早熟性状进行QTL初步定位,为分子标记辅助育种提供依据。利用5200多对SSR引物筛选海岛棉品种新海3号和Giza82间的多态性引物,获得107对。以多态性引物检测新海3号×Giza82的190个F2:3家系,获得120个多态性位点。利用JoinMap3.0分析软件构建了一个包含22个连锁群,74个标记,标记间平均距离12.06 cM,全长893 cM,覆盖海岛棉基因组20.12%的分子标记遗传连锁图谱。采用复合区间作图法检测到21个与海岛棉产量性状和早熟性状有关的QTL,其中早熟性状检测到12个QTL,分别位于1、3、5、6、11、17、22共7个连锁群上;产量性状检测到9个QTL,分别位于1、4、5、6、7、16、22共7个连锁群上。研究结果为海岛棉产量性状和早熟性状的分子设计育种提供了有用的信息。