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PubMed2005

Results on quantitative trait loci for flushing date in oaks can be transferred to different segregating progenies.

Flushing date (bud burst) is one of the most important traits for the adaptation to different environments and climates in the temperate zone. Because of their wide geographic distribution, Quercus robur L. and Q. petraea (Matt.) Liebl. are suitable as model plants to study the genetic basis of bud burst. QTLs (Quantitative Trait Loci) with comparatively large effects have been mapped in a former study in a Q. robur x Q. robur full-sib family (French cross). In the present study, we performed a Bulked Segregant Analysis (BSA) in the F (1) progeny comprising 144 seedlings derived from a cross between a single Q. robur tree as common seed parent and five different pollen donors both from Q. robur and Q. petraea (Q. robur x Q. spp., Diekholzen crosses). In addition, markers linked to two bud burst QTLs with comparably strong effect in the above-mentioned full-sib family (French cross) were tested for their association with bud burst in the Q. robur x Q. spp. (Diekholzen) progeny. Using three microsatellite markers as anchor points, we could map QTLs on linkage group 7 and on linkage group 2, together explaining 16.2 % of the total phenotypic variance (PVE) in 1999 and 38.1 % in 2003. Out of 10 markers that segregated in both mapping progenies, four markers including the two microsatellite markers, showed a significant effect on bud burst in both materials. At microsatellite loci ssrQpZAG1/5 (linkage group 7) and ssrQpZAG119 (linkage group 2) alleles associated with early (allele 166 bp in ssrQpZAG1/5) and late bud burst (allele 57 bp in ssrQpZAG119) in the Q. robur x Q. robur full-sib family (French cross) showed a highly significant association with the same polarity of the effect in the Q. robur x Q. spp. (Diekholzen) progeny. The usefulness of these markers for marker-assisted selection in full-sib and half-sib families is discussed.

Genetic Linkage↗

PubMed1999

Interacting quantitative trait loci control phenotypic variation in murine estradiol-regulated responses.

The steroid hormone estradiol (E2) elicits a spectrum of systemic and uterotropic responses in vivo. For example, E2 treatment of ovariectomized adult and sexually immature rodents leads to uterine leukocytic infiltration, cell proliferation, and organ growth. E2-regulated growth is also associated with a variety of normal and pathological phenotypes. Historically, the uterine growth response has been used as the key model to understand the molecular and biochemical mechanisms underlying E2-dependent growth. In this study, genome exclusion mapping identified two quantitative trait loci (QTL) in the mouse, Est2 and Est3 on chromosomes 5 and 11, respectively, that control the phenotypic variation in uterine wet weight. Both QTL are linked to a variety of E2-regulated genes, suggesting that they may represent loci within conserved gene complexes that play fundamental roles in mediating the effects of E2. Interaction and multiple trait analyses using the uterine leukocyte response and wet weight suggest that Est4, a QTL on chromosome 10, may encode an interacting factor that influences the quantitative variation in both responses. Our results show that E2-dependent responses can be genetically controlled and that a genetic basis may underlie the variation observed in many E2-dependent phenotypes.

Animals↗

PubMed2002

Interacting quantitative trait loci control loss of peripheral tolerance and susceptibility to autoimmune ovarian dysgenesis after day 3 thymectomy in mice.

Day 3 thymectomy (D3Tx) results in a loss of peripheral tolerance mediated by CD4(+)CD25(+) T cells and the development of autoimmune ovarian dysgenesis (AOD) in A/J and (C57BL/6J x A/J)F(1) (B6AF(1)) hybrids but not in C57BL/6J mice. Quantitative trait loci (QTL) linkage analysis using a B6AF(1) x C57BL/6J backcross population verified Aod1 and Aod2 that were previously mapped as qualitative traits. Additionally, three new QTL intervals, Aod3, Aod4, and Aod5, on chromosomes 1, 2, and 7, respectively, influencing specific subphenotypes of AOD were identified. QTL linkage analysis using the A x B and B x A recombinant inbred lines verified Aod3 and confirmed linkage to H2. Aod5 colocalized with Mater, an ovarian-specific autoantigen recognized by anti-ovarian autoantibodies in the sera of D3Tx mice. Sequence analysis of Mater identified allelic, strain-specific splice variants between A/J and C57BL/6J mice making it an attractive candidate gene for Aod5. Interaction analysis revealed significant epistatic effects between Aod1-5 and Gasa2, a locus associated with susceptibility to D3Tx-induced autoimmune gastritis, as well as with H2. These results indicate that the QTL controlling D3Tx-induced autoimmune phenomenon are both organ specific and more generalized in their effects with respect to the genesis and activity of the immunoregulatory mechanisms maintaining peripheral tolerance.

Amino Acid Sequence↗

PubMed2005

Quantitative trait loci mapping for intracellular calcium in spontaneously hypertensive rats.

BACKGROUND: Increased intracellular calcium ([Ca2+]i) in platelets is also proposed as an intermediate phenotype for hypertension in spontaneously hypertensive rats (SHR). Increased [Ca2+]i in platelets is hypothesized to contribute to atherothrombotic events. Platelet hyperactivity is frequently associated with cardiovascular disease. METHODS: In a genome scan, we performed the quantitative trait loci (QTL) mapping for [Ca2+]i in back-crossed rats derived from SHR and normotensive Fischer 344 rats, which demonstrated a single major QTL for hypertension on chromosome 1. Thrombin-stimulated [Ca2+]i in Ca2+-free and in Ca2+-containing buffers was measured in platelets using the Fura-2 method. RESULTS: Among the parental strains, systolic blood pressure and thrombin-stimulated [Ca2+]i were significantly greater in SHR than in Fischer 344 and F1 rats. The sarco(endo)plasmic reticulum Ca2+-dependent ATPase II gene locus (Serca2) between D12Mgh5 and D12Mgh6 showed the significant linkage for thrombin-stimulated [Ca2+]i in Ca2+-free and Ca2+-containing buffers. The peak logarithm of the odds scores were 3.6 and 3.3, respectively. These QTL explained 19.8% and 17.4% of the total variances, respectively. D3Mit13 and DXMgh1 showed suggestive linkage for thrombin-stimulated [Ca2+]i in Ca2+-free and in Ca2+-containing buffers, respectively. The peak logarithm of the odds scores were 2.6 and 2.1, respectively. CONCLUSIONS: A significant QTL for [Ca2+]i was mapped near Serca2 on chromosome 12, and suggestive QTL were identified near D3Mit13 and DXMgh1 in a genome scan. Genetic abnormalites in platelet [Ca2+]i may contribute to cardiovascular disease via platelet hyperactivity, independent of blood pressure elevation.

Animals↗

PubMed2003

Genetic mapping and analysis of quantitative trait loci affecting fiber and lignin content in maize.

Plant cell walls of forage provide a major source of energy for ruminant animals. Digestion of cell walls is limited by the presence of lignin, therefore the improving the digestibility of forages by reducing lignin content is a major goal in forage crop breeding programs. A recombinant inbred line maize population was used to map quantitative trait loci (QTL) for neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) of leaf-sheath and stalk tissues. All traits were positively genetically correlated. The larger genetic correlations were between NDF and ADF in sheaths (r = 0.84), NDF and ADF (r = 0.96), ADF and ADL (r = 0.83), and NDF and ADL (r = 0.76) in stalks. Twelve QTL were detected for NDF and 11 QTL for ADF in leaf-sheaths. Eight QTL detected for both traits were defined by the same or linked marker loci. Eight QTL were associated with leaf-sheath ADL. Eleven QTL were detected for NDF and ADF, and 12 QTL for ADL in stalks. Nine of eleven QTL detected for both NDF and ADF in stalks coincided in their genomic position. A high proportion of QTL detected for these traits had the same parental effects and genomic locations, suggesting that it is only necessary to select on one fiber component (NDF or ADF) to improve digestibility. Favorable correlated responses of unselected fiber components are expected due to coincident genomic locations of QTL and the high genetic correlation between fiber components. Several QTL detected in this study coincided in their positions with putative cellulose synthase genes from maize.

Cell Wall↗

PubMed2000

Mapping of quantitative trait loci for hypnotic sensitivity to ethanol in crosses derived from the C57BL/6 and DBA/2 mouse strains.

BACKGROUND: Acute ethanol sensitivity is thought to be a predisposing factor toward the development of alcoholism. Accumulated evidence suggests that this characteristic may be at least partly heritable. A widely accepted approach for identifying genes thought to contribute to alcoholism is to map quantitative trait loci (QTLs) for various ethanol-related behaviors in rodent models. METHODS: Ethanol sensitivity QTLs were interval-mapped in a C57BL/6 (B6) X DBA/2 (D2) F2 intercross that contained 391 mice. Sensitivity was measured as the duration of loss of righting reflex (LORR) after 4.1 g/kg ip. LORR also was evaluated in a chromosome 1 marker-assisted congenic strain that had an approximately 30 centiMorgan (cM) portion of D2 DNA from the distal end of chromosome 1 introgressed onto a B6 background. RESULTS: A suggestive QTL was mapped on chromosome 1 (LOD = 3.3; approximately 80 cM) and a provisional QTL on chromosome 5 (LOD = 2.3; approximately 26 cM). The provisional chromosome 5 QTL was found to be sex-specific (LOD = 2.5 for males; LOD < 1 for females) with the D2 allele increasing LORR. The chromosome 1 D2 allele decreased LORR. Consistent with the F2 QTL mapping, congenic mice heterozygous for the chromosome 1 interval (B6/D2) had a significantly different mean (+/- SEM) LORR of 74.0 +/- 4.9 min (n = 36) compared with 90.8 +/- 6.2 min (n = 33) for their homozygous (B6/B6) littermates (p = 0.02). Blood ethanol concentration at regain of righting reflex was 377 +/- 10 mg% for the B6/D2 and 368 +/- 10 mg% (p = NS) for the B6/B6. CONCLUSIONS: LORR results in the chromosome 1 congenic mice were consistent with and very similar to what was predicted from the QTL analysis in the B6 X D2 F2 population. These results support a suggestive LORR QTL on the distal end of mouse chromosome 1. The results also indicate that there is a provisional sex-specific LORR QTL on chromosome 5.

Alcoholism↗

PubMed2002

Functional mapping of quantitative trait loci underlying the character process: a theoretical framework.

Unlike a character measured at a finite set of landmark points, function-valued traits are those that change as a function of some independent and continuous variable. These traits, also called infinite-dimensional characters, can be described as the character process and include a number of biologically, economically, or biomedically important features, such as growth trajectories, allometric scalings, and norms of reaction. Here we present a new statistical infrastructure for mapping quantitative trait loci (QTL) underlying the character process. This strategy, termed functional mapping, integrates mathematical relationships of different traits or variables within the genetic mapping framework. Logistic mapping proposed in this article can be viewed as an example of functional mapping. Logistic mapping is based on a universal biological law that for each and every living organism growth over time follows an exponential growth curve (e.g., logistic or S-shaped). A maximum-likelihood approach based on a logistic-mixture model, implemented with the EM algorithm, is developed to provide the estimates of QTL positions, QTL effects, and other model parameters responsible for growth trajectories. Logistic mapping displays a tremendous potential to increase the power of QTL detection, the precision of parameter estimation, and the resolution of QTL localization due to the small number of parameters to be estimated, the pleiotropic effect of a QTL on growth, and/or residual correlations of growth at different ages. More importantly, logistic mapping allows for testing numerous biologically important hypotheses concerning the genetic basis of quantitative variation, thus gaining an insight into the critical role of development in shaping plant and animal evolution and domestication. The power of logistic mapping is demonstrated by an example of a forest tree, in which one QTL affecting stem growth processes is detected on a linkage group using our method, whereas it cannot be detected using current methods. The advantages of functional mapping are also discussed.

Chromosome Mapping↗

PubMed2000

Identification of quantitative trait loci influencing alcohol consumption in the high alcohol drinking and low alcohol drinking rat lines.

Selective breeding has been employed to develop high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) rat lines from the heterogeneous N/Nih rat. Within-family selection and a rotational breeding design were used to discourage inbreeding (Li et al, 1993). To identify quantitative trait loci (QTLs) contributing to alcohol consumption, reciprocal HAD and LAD matings in conjunction with F1 intercrosses were used to create 459 F2 progeny. Using selective genotyping of 151 F2 progeny with extreme alcohol consumption scores and a novel least squares method developed by Haley et al (1994), five chromosomal regions (1, 5, 10, 12, and 16) were identified with lod scores greater than 2.0. Genotyping of the entire sample of 459 F2 progeny produced maximum lod scores of 3.5 on chromosome 5, 2.4 on chromosome 10, 4.7 on chromosome 12 and 2.9 on chromosome 16. The evidence of linkage to chromosome 1 diminished substantially to a maximum lod score of 0.5 when all F2 progeny were genotyped. This study is the first genome-wide study for QTLs underlying alcohol consumption that has employed noninbred lines. Further localization of these QTLs will likely provide insight and candidate genes for the study of human alcoholism.

Alcohol Drinking↗

PubMed2004

Two quantitative trait loci affect ACE activities in Mexican-Americans.

Angiotensin-converting enzyme (ACE) activity is highly heritable and has been associated with cardiovascular disease. We are studying the effects of genes and environmental factors on hypertension and related phenotypes, such as ACE activity, in Mexican-American families. In the current study, we performed multipoint linkage analysis to search for quantitative trait loci (QTLs) that affect ACE activities on data from 793 individuals from 29 pedigrees from the San Antonio Family Heart Study. As expected, we obtained strong evidence (maximum log of the odds [LOD]=4.57, genomic P=0.003) that a QTL for ACE activity is located on chromosome 17 near the ACE structural locus. We subsequently performed linkage analyses conditional on the effect of this QTL and obtained strong evidence (LOD=3.34) for a second QTL on chromosome 4 near D4S1548. We next incorporated the ACEIns/Del genotypes in our analyses and removed the evidence for the chromosome 17 QTL (maximum LOD=0.60); however, we retained our evidence for the QTL on chromosome 4q. We conclude that the QTL on chromosome 17 is tightly linked to ACE and is in strong disequilibrium with the insertion/deletion polymorphism, which is consistent with other reports. We also have evidence that an additional QTL affects ACE activity. Identification of this additional QTL might lead to alternate means of prophylaxis.

Adolescent↗

PubMed2002

Evaluation of quantitative trait loci regulating severity of mycobacterial adjuvant-induced arthritis in monocongenic and polycongenic rats: identification of a new regulatory locus on rat chromosome 10 and evidence of overlap with rheumatoid arthritis susceptibility loci.

OBJECTIVE: To evaluate the regulatory potential of genetic loci controlling Mycobacterium butyricum adjuvant-induced arthritis (Mbt-AIA) using mono- and polycongenic rats. METHODS: Of 4 quantitative trait loci (QTLs) that regulate Mbt-AIA, F344 alleles at 3 of these loci, Aia1, Aia2, and Aia3, are associated with lower arthritis severity, whereas F344 alleles at Aia4 are associated with greater arthritis severity. In this study, we constructed congenic lines by transferring 1 or more of the F344 genomic segments containing Aia1, Aia2, and Aia3 onto the DA genome. We comparatively evaluated their responses to Mbt-AIA with the responses of parental DA and F344 rats. RESULTS: Aia1, encompassing the rat major histocompatibility complex, reduced arthritis severity in monocongenic rats of both sexes. The arthritis-lowering effects of Aia2 and Aia3 were sex-influenced and were therefore observed in only males and only females, respectively. Polycongenic rats containing F344 genomic regions at Aia1, Aia2, and Aia3 developed Mbt-AIA of relatively greater severity than did F344 rats, implying that in DA and F344 rats, there could be other Mbt-AIA loci in addition to Aia1, Aia2, Aia3, and Aia4. To test the possibility that some of these Mbt-AIA-regulatory loci may colocalize with other arthritis QTLs, we evaluated Mbt-AIA in DA.F344 monocongenic rats containing collagen-induced arthritis QTLs. Cia5 (the QTL region on chromosome 10), but not Cia5a, Cia4, or Cia6, also regulated Mbt-AIA, and was named Aia5. CONCLUSION: F344 genomic regions at Aia1, Aia2, and Aia3 and the newly identified Aia5 contain genes that reduce Mbt-AIA severity in DA rats. These Mbt-AIA-regulatory loci overlap rheumatoid arthritis-susceptibility loci in humans.

Alleles↗

PubMed2025

Quantitative trait loci for Globodera pallida resistance derived from wild potato species Solanum gourlayi.

Globodera pallida is a major pest that is responsible for huge losses in potato yields worldwide. Expanding the gene pool of cultivated potatoes with clones resistant to this pest is made possible by searching for resistance genes in wild Solanum species. The aim of this study was to identify quantitative trait loci (QTLs) for potato resistance to Globodera pallida derived from Solanum gourlayi. A resistant diploid potato clone, Sg 2/7 (Solanum gourlayi, accession CGN17592), was crossed with a susceptible potato hybrid clone, DW 94-4235, to generate an F1 mapping population. All clones were tested for nematode resistance using G. pallida, pathotypes Pa2 and Pa3, in 2 or 3 years (2017-2019), respectively. Diversity Array Technology (DArTseq) was used for genotyping and genetic map construction. QTLs for nematode resistance were identified on potato chromosomes II, IV, V, VI, VII, X, XI, and XII, explaining from 10.1 to 21.5% of phenotypic variance. The most significant QTL for resistance to G. pallida pathotype Pa2 was identified on chromosome XII, explaining 20.9% of the phenotypic variance in the dataset from 2017. The most significant QTL for resistance to the G. pallida Pa3 pathotype was identified on chromosome VI, with a CAPS marker Exp928 in its peak, explaining 21.5% of the phenotypic variance in the dataset from 2017. The novel QTLs for resistance to S. gourlayi may be useful for breeding resistant potato cultivars, further studies of candidate genes, and host responses of potato to G. pallida infection.

Quantitative Trait Loci↗

PubMed2005

Quantitative trait locus analysis of atherosclerosis in an intercross between C57BL/6 and C3H mice carrying the mutant apolipoprotein E gene.

Inbred mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) differ significantly in atherosclerosis susceptibility and plasma lipid levels on the apolipoprotein E-deficient (apoE-/-) background when fed a Western diet. To determine genetic factors contributing to the variations in these phenotypes, we performed quantitative trait locus (QTL) analysis using an intercross between the two strains carrying the apoE-/- gene. Atherosclerotic lesions at the aortic root and plasma lipid levels of 234 female F2 mice were analyzed after being fed a Western diet for 12 weeks. QTL analysis revealed one significant QTL, named Ath22 (42 cM, LOD 4.1), on chromosome 9 and a suggestive QTL near D11mit236 (20 cM, LOD 2.4) on chromosome 11 that influenced atherosclerotic lesion size. One significant QTL on distal chromosome 1, which accounted for major variations in plasma LDL/VLDL cholesterol and triglyceride levels, coincided with a QTL having strong effects on body weight. Plasma LDL/VLDL cholesterol or triglyceride levels of F2 mice were significantly correlated with body weight, but they were not correlated with atherosclerotic lesion sizes. These data indicate that atherosclerosis susceptibility and plasma cholesterol levels are controlled by separate genetic factors in the B6 and C3H mouse model and that genetic linkages exist between body weight and lipoprotein metabolism.

Animals↗

PubMed1996

Combining extremely concordant sibpairs with extremely discordant sibpairs provides a cost effective way to linkage analysis of quantitative trait loci.

Extremely discordant (ED) sibpairs have been shown to be very powerful for linkage analysis of human quantitative traits [Risch and Zhang (1995) Science 268: 1584-1589]. In many cases, the extremely concordant (EC) sibpairs collected in the process of screening for ED sibpairs carry valuable information for linkage. Therefore, it seems justifiable to investigate the advantages of genotyping and to include them with the ED sibpairs for linkage analysis. Herein we explore the distributions of EC as well as ED sibpairs under various genetic models and provide a basis for combining both types of sibpairs. A simple statistic testing means of genes shared identical by descent (IBD) in applied to combine both types of EC sibpairs (high-high and low-low) with the ED pairs. We show that when a decent number of EC pairs is added to the ED sample for analysis, the power is much enhanced, making it especially desirable when the number of available ED pairs is small. We show at the same time that combining EC pairs with ED pairs is more cost effective than pursuing ED sibpairs alone.

Costs and Cost Analysis↗

PubMed1995

How can maximum likelihood methods reveal candidate gene effects on a quantitative trait?

Different maximum likelihood approaches were used to explore the role of candidate genes in the variability of quantitative trait Q1 while accounting for the effects of age, Q2, and Q3. Segregation analysis, under the class D regressive model, provides evidence for a Mendelian gene effect on the adjusted trait Q1. Results of gene mapping through lod-score analyses remain puzzling. Pairwise lod scores indicate a possible linkage with the candidate gene C5 which is excluded when using tightly linked informative marker loci. Finally, our combined segregation and linkage analysis clearly shows that a C5 linked gene is involved in Q1 variability. However, given the lod-score results within the C5 region, we postulate a more complex mechanism for Q1 than a single di-allelic C5 linked gene. The knowledge of the true model (C5 is MG1 and has three alleles) permits a partial explanation of our results. This study demonstrates the advantages of using complementary approaches to reveal the role of candidate genes in complex traits, and the value of simultaneous estimation of linkage and segregation parameters.

Alleles↗

PubMed1997

Assessment of learning by the Morris water task and fear conditioning in inbred mouse strains and F1 hybrids: implications of genetic background for single gene mutations and quantitative trait loci analyses.

Genetic methods including the creation of transgenic or null mutant models and mapping studies using quantitative trait loci strategies can be used to identify candidate genes in mice that regulate learning processes. Interpretations as to the impact of single gene mutations for polygenic behaviours like learning will depend in part on the genetic background of the animals used for these manipulations. To address the issue of genetic variability, 12 inbred strains and seven different F1 hybrids were tested on multiple behavioural tasks, including two complex learning paradigms: the Morris water task and fear conditioning. Strain differences were found for all variables measured. In the hidden platform version of the Morris task, the albino animals performed poorly while overall the F1 hybrids showed the best selectivity for the trained quadrant as measured in a probe trial. In contrast, almost all genotypes performed well on the contextual fear conditioning task and learned to associate the test context with the pairing of a foot shock and auditory stimulus as demonstrated 24 h after training by increased freezing in the test environment compared to an altered context. Significant genetic correlations were obtained for behavioural measures suggesting that the same genes regulate various aspects of performance on behavioural tasks. Scores from these multiple inbred strains and F1 hybrids provide a baseline level of learning ability for fear conditioning and the Morris water task. The results of the present study confirm the importance of genetic background in the performance of various learning tasks. This variability should be considered when developing new transgenic or null mutant animal models.

Acoustic Stimulation↗

PubMed1993

Detection of quantitative trait loci from frequency changes of marker alleles under selection.

A method was developed to estimate effects of quantitative trait loci (QTL) by maximum likelihood using information from changes of gene frequency at marker loci under selection, assuming an additive model of complete linkage between markers and QTL. The method was applied to data from 16 molecular and coat colour marker loci in mouse lines derived from the F2 of two inbred strains which were divergently selected on 6-week weight for 21 generations. In 4 regions of the genome, marker allele frequencies were more extreme than could be explained by sampling, implying selection at nearby QTL. An effect of about 0.5 standard deviations was located on chromosome 11, and accounted for nearly 10% of the genetic variance in the base population. QTL with effects as small as 0.2 phenotypic standard deviations could be detected. For typing of a given number of individuals, the power of detection of QTL is very high compared to, for example, analysis of an F2 population. The joint effects of linkage and selection were investigated by Monte Carlo simulation. Marker gene frequencies change little as a consequence of selection at a QTL unless the marker and QTL are less than about 20 cM apart.

Alleles↗

PubMed1994

A pleiotropic nonadditive model of variation in quantitative traits.

A model of mutation-selection-drift balance incorporating pleiotropic and dominance effects of new mutations on quantitative traits and fitness is investigated and used to predict the amount and nature of genetic variation maintained in segregating populations. The model is based on recent information on the joint distribution of mutant effects on bristle traits and fitness in Drosophila melanogaster from experiments on the accumulation of spontaneous and P element-induced mutations. These experiments suggest a leptokurtic distribution of effects with an intermediate correlation between effects on the trait and fitness. Mutants of large effect tend to be partially recessive while those with smaller effect are on average additive, but apparently with very variable gene action. The model is parameterized with two different sets of information derived from P element insertion and spontaneous mutation data, though the latter are not fully known. They differ in the number of mutations per generation which is assumed to affect the trait. Predictions of the variance maintained for bristle number assuming parameters derived from effects of P element insertions, in which the proportion of mutations with an effect on the trait is small, fit reasonably well with experimental observations. The equilibrium genetic variance is nearly independent of the degree of dominance of new mutations. Heritabilities of between 0.4 and 0.6 are predicted with population sizes from 10(4) to 10(6), and most of the variance for the metric trait in segregating population is due to a small proportion of mutations (about 1% of the total number) with neutral or nearly neutral effects on fitness and intermediate effects on the trait (0.1-0.5 sigma P).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Identification of quantitative trait loci influencing wood specific gravity in an outbred pedigree of loblolly pine.

We report the identification of quantitative trait loci (QTL) influencing wood specific gravity (WSG) in an outbred pedigree of loblolly pine (Pinus taeda L.). QTL mapping in an outcrossing species is complicated by the presence of multiple alleles (> 2) at QTL and marker loci. Multiple alleles at QTL allow the examination of interaction among alleles at QTL (deviation from additive gene action). Restriction fragment length polymorphism (RFLP) marker genotypes and wood specific gravity phenotypes were determined for 177 progeny. Two RFLP linkage maps were constructed, representing maternal and paternal parent gamete segregations as inferred from diploid progeny RFLP genotypes. RFLP loci segregating for multiple alleles were vital for aligning the two maps. Each RFLP locus was assayed for cosegregation with WSG QTL using analysis of variance (ANOVA). Five regions of the genome contained one or more RFLP loci showing differences in mean WSG at or below the P = 0.05 level for progeny as grouped by RFLP genotype. One region contained a marker locus (S6a) whose QTL-associated effects were highly significant (P > 0.0002). Marker S6a segregated for multiple alleles, a prerequisite for determining the number of alleles segregating at the linked QTL and analyzing the interactions among QTL alleles. The QTL associated with marker S6a appeared to be segregating for multiple alleles which interacted with each other and with environments. No evidence for digenic epistasis was found among the five QTL.

Alleles↗