Detection of quantitative trait loci for body weights and conformation traits in Beijing ducks

Quantitative trait loci (QTL) for body weights and conformation traits were detected in Beijing ducks. Traits included body weights (BW) at hatching and at 1-7 weeks of age; lengths of the body (BL), keel bone (KBL), shank (SL) and neck (NL) at 7 weeks of age; width of breast (BTW) at 7 weeks; and girths of shank (SG) and breast (BG) at 7 weeks. Using a half-sib analysis with a multiple-QTL model, linkage between the phenotypic traits and 95 microsatellite markers was studied. Six genome-wide suggestive QTL for three body weights and two conformation traits were identified in CAU1, CAU2, CAU6 and CAU12. Chromosome-wide significant QTL influencing one body weight trait and one conformation trait were located in CAU4 and CAU10 respectively. Twelve chromosome-wide suggestive QTL for six body weight traits and four conformation traits were found in seven linkage groups (CAU1, CAU2, CAU3, CAU4, CAU6, CAU10 and CAU12). In addition, the QTL in CAU6 at 21 and 73 cM jointly affected SG and explained 10.6% of the phenotypic variation. This study provides the first evidence for QTL involved in body weights and conformation traits in ducks, and will stimulate further investigations into the genetic architecture of these traits in this species.     

A genome scan reveals QTL for growth, fatness, leanness and meat quality in a Duroc-Pietrain resource population

We performed a genome-wide QTL scan for production traits in a line cross between Duroc and Pietrain breeds of pigs, which included 585 F(2) progeny produced from 31 full-sib families genotyped with 106 informative microsatellites. A linkage map covering all 18 autosomes and spanning 1987 Kosambi cM was constructed. Thirty-five phenotypic traits including body weight, growth, carcass composition and meat quality traits were analysed using least square regression interval mapping. Twenty-four QTL exceeded the genome-wide significance threshold, while 47 QTL reached the suggestive threshold. These QTL were located at 28 genomic regions on 16 autosomal chromosomes and QTL in 11 regions were significant at the genome-wide level. A QTL affecting pH value in loin was detected on SSC1 between marker-interval S0312-S0113 with strong statistical support (P < 3.0 x 10(-14)); this QTL was also associated with meat colour and conductivity. QTL for carcass composition and average daily gain was also found on SSC1, suggesting multiple QTL. Seventeen genomic segments had only a single QTL that reached at least suggestive significance. Forty QTL exhibited additive inheritance whereas 31 QTL showed (over-) dominance effects. Two QTL for trait backfat thickness were detected on SSC2; a significant paternal effect was found for a QTL in the IGF2 region while another QTL in the middle of SSC2 showed Mendelian expression.     

A genome-wide scan for quantitative trait loci affecting serum glucose and lipids in a White Duroc × Erhualian intercross F2 population

Serum glucose and lipid levels are associated with diabetes mellitus and cardiovascular disease. The purpose of this study was to identify quantitative trait loci (QTL) for serum glucose and lipids in a White Duroc × Erhualian resource population. Serum glucose, glycosylated serum proteins (GSP), and serum lipid levels were measured in a total of 760 F₂ animals at 240 days. Strong positive correlations were observed between total cholesterol (TC) and low-density-lipoprotein cholesterol (LDL-C)/high-density-lipoprotein cholesterol (HDL-C). A whole-genome scan was performed with 194 microsatellites covering the pig genome across the entire resource population, revealing 2 QTL for serum glucose and 15 QTL for serum lipids. Of them, three 1% genome-wide significant QTL were identified for LDL-C, TC, and triglycerides (TG) in an adjacent region (67–73 cM) on chromosome 2 (SSC2), and the QTL for LDL-C showed the largest effect with a 95% confidence interval of 5 cM. Another 1% genome-wide significant QTL was found for LDL-C at 87 cM on SSC8. Other QTL showed 5% genome-wide significant or suggestive effects on SSC4, 5, 7, 9, 11, 14, and 15. In total, five significant QTL for serum lipids and a suggestive QTL for GSP on SSC4 were identified for the first time in pigs. Most of the identified QTL are homologous to the previously reported QTL for serum lipids in humans and mice. As correlated traits, QTL for TC and LDL-C were always located in the same genomic regions. The results shed new light on studies of human atherosclerosis and cardiovascular-related diseases. R. Chen, J. Ren, and W. Li contributed equally to this work.     

Mapping of quantitative trait loci for flesh colour and growth traits in Atlantic salmon (Salmo salar)

Background

Flesh colour and growth related traits in salmonids are both commercially important and of great interest from a physiological and evolutionary perspective. The aim of this study was to identify quantitative trait loci (QTL) affecting flesh colour and growth related traits in an F2 population derived from an isolated, landlocked wild population in Norway (Byglands Bleke) and a commercial production population.

Methods

One hundred and twenty-eight informative microsatellite loci distributed across all 29 linkage groups in Atlantic salmon were genotyped in individuals from four F2 families that were selected from the ends of the flesh colour distribution. Genotyping of 23 additional loci and two additional families was performed on a number of linkage groups harbouring putative QTL. QTL analysis was performed using a line-cross model assuming fixation of alternate QTL alleles and a half-sib model with no assumptions about the number and frequency of QTL alleles in the founder populations.

Results

A moderate to strong phenotypic correlation was found between colour, length and weight traits. In total, 13 genome-wide significant QTL were detected for all traits using the line-cross model, including three genome-wide significant QTL for flesh colour (Chr 6, Chr 26 and Chr 4). In addition, 32 suggestive QTL were detected (chromosome-wide P < 0.05). Using the half-sib model, six genome-wide significant QTL were detected for all traits, including two for flesh colour (Chr 26 and Chr 4) and 41 suggestive QTL were detected (chromosome-wide P < 0.05). Based on the half-sib analysis, these two genome-wide significant QTL for flesh colour explained 24% of the phenotypic variance for this trait.

Conclusions

A large number of significant and suggestive QTL for flesh colour and growth traits were found in an F2 population of Atlantic salmon. Chr 26 and Chr 4 presented the strongest evidence for significant QTL affecting flesh colour, while Chr 10, Chr 5, and Chr 4 presented the strongest evidence for significant QTL affecting growth traits (length and weight). These QTL could be strong candidates for use in marker-assisted selection and provide a starting point for further characterisation of the genetic components underlying flesh colour and growth.     

Quantitative trait loci for litter size and prenatal loss in a White Duroc × Chinese Erhualian resource population

To detect quantitative trait loci (QTL) for litter size related traits, the total number of born piglets (TNB), the number of born alive piglets (NBA), the number of stillborn piglets (NSB) and the number of mummies (NM) at the first parity were recorded in 299 F₂ sows in a White Duroc × Chinese Erhualian intercross resource population. A whole genome scan was performed with 183 microsatellites distributed across 19 porcine chromosomes in the resource population, and the QTL analysis was performed with a least-squares method. A 5% genome-wide significant QTL was detected at 88 cM on pig chromosome (SSC) 15 for NBA, which also showed suggestive effect on TNB. In addition, four suggestive QTL were detected on SSC 6, 7, 8 and 15 for TNB, NBA or NSB. Two of the five QTL detected showed accordance with previous reports. No QTL was found for NM.     

QTL for body weight and condition factor in Atlantic salmon (Salmo salar): comparative analysis with rainbow trout (Oncorhynchus mykiss) and Arctic charr (Salvelinus alpinus)

Genotypes at 91 microsatellite loci in three full-sib families were used to search for QTL affecting body weight (BW) and condition factor in North American Atlantic salmon (Salmo salar). More than one informative marker was identified on 16-18 linkage groups in each family, allowing at least one chromosomal interval to be analyzed per linkage group. Two significant QTL for BW on linkage groups AS-8 and AS-11, and four significant QTL for condition factor on linkage groups AS-2, AS-5, AS-11, and AS-14 were identified. QTL for both BW and condition factor were located on linkage groups AS-1, 6, 8, 11, and 14 when considering both significant and suggestive QTL effects. The largest QTL effects for BW (AS-8) and for condition factor (AS-14) accounted for 20.1 and 24.9% of the trait variation, respectively. Three of the QTL for BW occur on linkage groups where similar effects have been detected on the homologous regions in either rainbow trout (Oncorhynchus mykiss) or Arctic charr (Salvelinus alpinus).     

A genome scan for quantitative trait loci affecting three ear traits in a White Duroc × Chinese Erhualian resource population

Chinese Erhualian pigs have larger and floppier ears compared with White Duroc pigs (small, half- or fully-pricked ears). To identify quantitative trait loci (QTL) for ear weight and area as well as erectness, a genome-wide scan with 194 microsatellites was performed in a White Duroc × Chinese Erhualian resource population (>1000 F₂ animals). Twenty-three genome-wide significant QTL and 12 suggestive QTL were identified. All QTL for ear erectness and size detected in two previous studies, bar two on SSC6 and 9, were confirmed here. The 1% genome-wide significant QTL at 70 cM on SSC5 and at 58 cM on SSC7 have profound and pleiotropic effects on the three ear traits, with Erhualian alleles increasing weight and area but decreasing erectness. Notably, the 95% confidence interval of the QTL for weight and area on SSC7 spanned only 3 cM. New QTL reaching 1% genome-wide significance were found on SSC8 (at 37 cM) for all three ear traits, on SSC4 and 16 for weight and area, and on SSCX for area. Unexpectedly, Erhualian alleles at these loci were associated with lighter and smaller or erect ear. Some new suggestive QTL were also found on other chromosome regions. Almost all the QTL for weight and area had essentially additive effects, while the QTL for erectness on SSC2, 5 and 7 showed not only additive effects but also partial dominance effects of Erhualian alleles. The two most significant QTL on SSC7 and SSC5 could be promising targets for fine mapping and identification of the causative mutations.     

Quantitative trait loci for production traits in pigs: a combined analysis of two Meishan x Large White populations

Combined analysis of data from two or more resource populations can improve the power and accuracy of QTL mapping and allow some cross-validation of results. In this study, we performed a genome-wide scan using combined data from two F(2) populations derived from a cross between Large White and Chinese Meishan pigs. A total of 739 pigs were included in the analysis. In total 187 markers were genotyped in the two populations, including 115 markers genotyped in both populations, and these markers covered 2282 cM of the pig genome with an average of 13.58 cM between markers. Seven traits (teat number, birth weight, weaning weight, test-end weight, fat depth at shoulder, fat depth at mid back and fat depth at loin) were analysed for both individual populations and the combined population. There were 9 (2, 10), 1 (4, 4) and 14 (5, 18) QTL that achieved 1% genome-wide, 5% genome-wide and suggestive significance levels respectively in population 1 (population 2, combined population). Additive effects of QTL detected in the two populations at all significance levels were largely consistent suggesting that the QTL represent real genetic effects, but this was not the case for dominance or imprinting effects. There were also a number of significant interactions between detected QTL effects and population.     

Selection for tonic immobility duration does not affect the response to novelty in quail

Genetic selection on a single fear test, the tonic immobility test, seems to result in selection on fearfulness, i.e. the propensity to exhibit fear responses, whatever the fear tests used. However, the conception of fear as a single variable has been challenged by the recognition that fear is multidimensional. This study was designed to test whether genetic selection on a classic index of fear in birds, tonic immobility duration, is accompanied by changes in the response to a single dimension of fear – novelty.Two lines of quail divergently selected for long (LTI) or short (STI) duration of tonic immobility were exposed to a novel object in their home cage. Quail of both lines showed typical fear reactions in response to novelty but there was no difference between lines. We conclude that genetic selection for tonic immobility duration does not affect all dimensions of fear, notably not novelty. Further studies are needed to investigate the dimensions of fear on which the two lines of quail could have been selected.     

Mapping QTL for growth and shank traits in chickens divergently selected for high or low body weight

An F₂ population (695 individuals) was established from broiler chickens divergently selected for either high (HG) or low (LG) growth, and used to localize QTL for developmental changes in body weight (BW), shank length (SL9) and shank diameter (SD9) at 9 weeks. QTL mapping revealed three genome‐wide QTL on chromosomes (GGA) 2, 4 and 26 and three suggestive QTL on GGA 1, 3 and 5. Most of the BW QTL individually explained 2–5% of the phenotypic variance. The BW QTL on GGA2 explained about 7% of BW from 3 to 7 weeks of age, while that on GGA4 explained 15% of BW from 5 to 9 weeks. The BW QTL on GGA2 and GGA4 could be associated with early and late growth respectively. The GGA4 QTL also had the largest effect on SL9 and SD9 and explained 7% and 10% of their phenotypic variances respectively. However, when SL9 and SD9 were corrected with BW9, a shank length percent QTL was identified on GGA2. We identified novel QTL and also confirmed previously identified loci in other chicken populations. As the foundation population was established from commercial broiler strains, it is possible that QTL identified in this study could still be segregating in commercial strains.     

A whole genome scan to detect quantitative trait loci for gestation length and sow maternal ability related traits in a White Duroc × Erhualian F2 resource population

Gestation length and maternal ability are important to improve the sow reproduction efficiency and their offspring survival. To map quantitative trait loci (QTL) for gestation length and maternal ability related traits including piglet survival rate and average body weight of piglets at weaning, more than 200 F2 sows from a White Duroc × Erhualian resource population were phenotyped. A genome-wide scan was performed with 194 microsatellite markers covering the whole pig genome. QTL analysis was carried out using a composite regression interval mapping method via QTL express. The results showed that total number of born piglets was significantly correlated with gestation length (r = -0.13, P < 0.05). Three QTL were detected on pig chromosome (SSC)2, 8 and 12 for gestation length. The QTL on SSC2 achieved the 5% genome-wide significant level and the QTL on SSC8 was consistent with previous reports. Four suggestive QTL were identified for maternal ability related traits including 1 QTL for survival rate of piglets at weaning on SSC8, 3 QTL for average body weight of piglet at weaning on SSC3, 11 and 13.     

A whole genome scanning for quantitative trait loci on traits related to sperm quality and ejaculation in pigs

To identify quantitative trait loci (QTL) for traits related to semen and ejaculation, phenotype data including semen volume, sperm concentration, total sperm per ejaculate, sperm motility, sperm abnormality rate, semen pH value, ejaculation times and ejaculation duration were measured on 206 F(2) boar at 240 days in a White Duroc x Erhualian intercross. A genome-wide scan was performed and the entire White Duroc x Erhualian intercross was genotyped for 183 microsatellite markers covering the whole pig genome. QTL analysis was performed using a composite regression interval mapping method via QTLExpress. A total of 18 QTL were detected, including 4 genome-wide significant QTL each for semen pH on pig chromosome (SSC) 2 and SSC12, for semen volume on SSC15, and for ejaculation times on SSC17. Fourteen suggestive QTL were found on SSC1, 2, 3, 4, 6, 9, 17 and 18. To our knowledge, this is the first report about the QTL for semen and ejaculation traits in pigs, providing a start point to decipher the genetic basis of these complex traits.     

Sex- and lineage-specific inheritance of depression-like behavior in the rat

The Wistar–Kyoto (WKY) rat exhibits physiological and behavioral similarities to endophenotypes of human depression. In the forced swim test (FST), a well-characterized antidepressant-reversible test for behavioral despair in rodents, WKYs express characteristics of behavioral despair; increased immobility, and decreased climbing. To map genetic loci linked to behavior in the FST, we conducted a quantitative trait loci (QTL) analysis of the segregating F2 generation of a WKY × Fisher 344 (F344) reciprocal intercross. Using linear-model-based genome scans to include covariate (sex or lineage)-by-QTL interaction effects, four significant QTL influencing climbing behavior were identified. In addition, we identified three, seven, and two suggestive QTL for climbing, immobility, and swimming, respectively. One of these loci was pleiotropic, affecting both immobility and climbing. As found in human linkage studies, several of these QTL showed sex- and/or lineage-dependent effects. A simultaneous search strategy identified three epistatic locus pairs for climbing. Multiple regression analysis was employed to characterize the joint contributions of these QTL and to clarify the sex- and lineage-dependent effects. As expected for complex traits, FST behavior is influenced by multiple QTL of small effect, each contributing 5%–10%, accounting for a total 10%–30% of the phenotypic variance. A number of loci mapped in this study share overlapping candidate regions with previously identified emotionality QTL in mice as well as with susceptibility loci recognized by linkage or genome scan analyses for major depression or bipolar disorder in humans. The presence of these loci across species suggests that these QTL may represent universal genetic factors contributing to mood disorders.     

Genetic architecture of body weight,condition factor and age of sexual maturation in Icelandic Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>)

The high commercial value from the aquaculture of salmonid fishes has prompted many studies into the genetic architecture of complex traits and the need to identify genomic regions that have repeatable associations with trait variation both within and among species. We searched for quantitative trait loci (QTL) for body weight (BW), condition factor (CF) and age of sexual maturation (MAT) in families of Arctic charr (Salvelinus alpinus) from an Icelandic breeding program. QTL with genome-wide significance were detected for each trait on multiple Arctic charr (AC) linkage groups (BW: AC-4, AC-20; CF: AC-7, AC-20, AC-23, AC-36; MAT: AC-13/34, AC-39). In addition to the genome-wide significant QTL for both BW and CF on AC-20, linkage groups AC-4, AC-7, AC-8, and AC-16 contain QTL for both BW and CF with chromosome-wide significance. These regions had effects (albeit weaker) on MAT with the exception of the region on AC-8. Comparisons with a North American cultured strain of Arctic charr, as well as North American populations of Atlantic salmon (Salmo salar), and rainbow trout (Oncorhynchus mykiss), reveal some conservation in QTL location and structure, particularly with respect to the joint associations of QTL influencing BW and CF. The detection of some differences in genetic architecture between the two aquaculture strains of Arctic charr may be reflective of the differential evolutionary histories experienced by these fishes, and illustrates the importance of including different strains to investigate genetic variation in a species where the intent is to use that variation in selective breeding programs.     

Quantitative trait loci with parent-of-origin effects in chicken

We investigated potential effects of parent-of-origin specific quantitative trait loci (QTL) in chicken. Two divergent egg-layer lines differing in egg quality were reciprocally crossed to produce 305 F2 hens. Searching the genome using models with uni-parental expression, we identified four genome-wide significant QTL with parent-of-origin effects and three highly suggestive QTL affecting age at first egg, egg weight, number of eggs, body weight, feed intake, and egg white quality. None of these QTL had been detected previously using Mendelian models. Two genome-wide significant and one highly suggestive QTL show exclusive paternal expression while the others show exclusive maternal expression. Each of the parent-of-origin specific QTL explained 3-5 % of the total phenotypic variance, with the effects ranging from 0.18 to 0.4 phenotypic SD in the F2. Using simulations and further detailed analyses, it was shown that departure from fixation in the founder lines, grand-maternal effects (i.e. mitochondrial or W-linked) and Z-linked QTL were unlikely to give rise to any spurious parent-of-origin effects. The present results suggest that QTL with parent-of-origin specific expression are a plausible explanation for some reciprocal effects in poultry and deserve more attention. An intriguing hypothesis is whether these effects could be the result of genomic imprinting, which is often assumed to be unique to eutherian mammals.     

Fear and distress in Japanese quail chicks of two lines genetically selected for low or high adrenocortical response to immobilization stress.

Behavioral and adrenocortical reactivity to stressful stimulation was examined in 12- and 13-day-old chicks of two lines of Japanese quail selected over several generations for exaggerated (HS: high stress) or reduced (LS: low stress) plasma corticosterone (B) response to brief immobilization stress. Plasma B concentrations and tonic immobility (TI) fear reactions were measured in unstressed (control) and stressed (overnight cooping) chicks of both lines. The stress treatment was applied over a period of 12-20 hr and it involved capture by the experimenter, inescapable exposure to an unfamiliar environment and to strange conspecifics, reductions in ambient temperature and floor space, and the deprivation of food and water. Chicks of the HS line were more susceptible to the induction of TI and they remained immobile longer than did LS chicks. Therefore HS chicks were considered to be more fearful than their LS counterparts. Stress treatment elicited a marked adrenocortical response that was more pronounced in HS than in LS chicks. Stress treatment also increased susceptibility to TI but did not significantly affect the duration of immobility. These findings suggest that selecting the quail for differential corticosterone response to a particular stressor had exerted an unconscious and concomitant effect on underlying fearfulness as well as on their adrenocortical reactivity to several other stressful situations. The results are further discussed in terms of a putative relationship between adrenocortical activation and fearfulness.     

A first-generation microsatellite linkage map of the Japanese quail

A linkage map of the Japanese quail (Coturnix japonica) genome was constructed based upon segregation analysis of 72 microsatellite loci in 433 F(2) progeny of 10 half-sib families obtained from a cross between two quail lines of different genetic origins. One line was selected for long duration of tonic immobility, a behavioural trait related to fearfulness, while the other was selected based on early egg production. Fifty-eight of the markers were resolved into 12 autosomal linkage groups and a Z chromosome-specific linkage group, while the remaining 14 markers were unlinked. The linkage groups range from 8 cM (two markers) to 206 cM (16 markers) and cover a total map distance of 576 cM with an average spacing of 10 cM between loci. Through comparative mapping with chicken (Gallus gallus) using orthologous markers, we were able to assign linkage groups CJA01, CJA02, CJA05, CJA06, CJA14 and CJA27 to chromosomes. This map, which is the first in quail based solely on microsatellites, is a major step towards the development of a quality molecular genetic map for this valuable species. It will provide an important framework for further genetic mapping and the identification of quantitative trait loci controlling egg production and fear-related behavioural traits in quail.     

Microsatellite mapping of quantitative trait loci affecting meat quality, stress hormones and production traits in Duroc × Large White F2 pigs

An F2 cross between Duroc and Large White pigs was carried out in order to detect quantitative trait loci (QTL) for 11 meat quality traits (L*, a* and b* Minolta coordinates and water-holding capacity (WHC) of two ham muscles, ultimate pH of two ham and one loin muscles), 13 production traits (birth weight, average daily gain during post-weaning and fattening periods, carcass fat depths at three locations, estimated lean meat content, carcass length and weights of five carcass cuts) and three stress hormone-level traits (cortisol, adrenaline and noradrenaline). Animals from the three generations of the experimental design (including 456 F2 pigs) were genotyped for 91 microsatellite markers covering all the autosomes. A total of 56 QTL were detected: 49 reached the chromosome-wide level (suggestive QTL with a maximal probability of 0.05) and seven were significant at the genome-wide level (with a probability varying from 6 × 10(-4) to 3 × 10(-3)). Twenty suggestive QTL were identified for ultimate pH, colour measurements and WHC on chromosome (SSC) 5, 6, 7, 8, 9, 11, 13, 14, 15 and 17. For production traits, 33 QTL were detected on all autosomes except SSC6, 8 and 9. Seven of these QTL, located on SSC2, 3, 10, 13, 16 and 17, exceeded the genome-wide significance threshold. Finally, three QTL were identified for levels of stress hormones: a QTL for cortisol level on SSC7 in the cortisol-binding globulin gene region, a QTL for adrenaline level on SSC10 and a QTL for noradrenaline level on SSC13. Among all the detected QTL, seven are described for the first time: a QTL for ultimate pH measurement on SSC5, two QTL affecting birth weight on SSC2 and 10, two QTL for growth rate on SSC15 (during fattening) and 17 (during post-weaning) and two QTL affecting the adrenaline and noradrenaline levels. For each QTL, only one to five of the six F1 sires were found to be heterozygous. It means that all QTL are segregating in at least one of the founder populations used in this study. These results suggest that both meat quality and production traits can be improved in purebred Duroc and Large White pigs through marker-assisted selection. It is of particular interest for meat quality traits, which are difficult to include in classical selection programmes.     

Mapping of multiple quantitative trait loci affecting bovine spongiform encephalopathy

A whole-genome scan was conducted to map quantitative trait loci (QTL) for BSE resistance or susceptibility. Cows from four half-sib families were included and 173 microsatellite markers were used to construct a 2835-cM (Kosambi) linkage map covering 29 autosomes and the pseudoautosomal region of the sex chromosome. Interval mapping by linear regression was applied and extended to a multiple-QTL analysis approach that used identified QTL on other chromosomes as cofactors to increase mapping power. In the multiple-QTL analysis, two genome-wide significant QTL (BTA17 and X/Y(ps)) and four genome-wide suggestive QTL (BTA1, 6, 13, and 19) were revealed. The QTL identified here using linkage analysis do not overlap with regions previously identified using TDT analysis. One factor that may explain the disparity between the results is that a more extensive data set was used in the present study. Furthermore, methodological differences between TDT and linkage analyses may affect the power of these approaches.     

QTL mapping for growth and carcass traits in an Iberian by Landrace pig intercross: additive,dominant and epistatic effects

Results from a QTL experiment on growth and carcass traits in an experimental F2 cross between Iberian and Landrace pigs are reported. Phenotypic data for growth, length of carcass and muscle mass, fat deposition and carcass composition traits from 321 individuals corresponding to 58 families were recorded. Animals were genotyped for 92 markers covering the 18 porcine autosomes (SSC). The results from the genomic scan show genomewide significant QTL in SSC2 (longissimus muscle area and backfat thickness), SSC4 (length of carcass, backfat thickness, loin, shoulder and belly bacon weights) and SSC6 (longissimus muscle area, backfat thickness, loin, shoulder and belly bacon weights). Suggestive QTL were also found on SSC1, SSC5, SSC7, SSC8, SSC9, SSC13, SCC14, SSC16 and SSC17. A bidimensional genomic scan every 10 cM was performed to detect interaction between QTL. The joint action of two suggestive QTL in SSC2 and SSC17 led to a genome-wide significant effect in live weight. The results of the bidimensional genomic scan showed that the genetic architecture was mainly additive or the experimental set-up did not have enough power to detect epistatic interactions.