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PubMed1995

Segregation and linkage analysis of serum angiotensin I-converting enzyme levels: evidence for two quantitative-trait loci.

Human serum angiotensin I-converting enzyme (ACE) levels vary substantially between individuals and are highly heritable. Segregation analysis in European families has shown that more than half of the total variability in ACE levels is influenced by quantitative-trait loci (QTL). One of these QTLs is located within or close to the ACE locus itself. Combined segregation/linkage analysis in a series of African Caribbean families from Jamaica shows that the ACE insertion-deletion polymorphism is in moderate linkage disequilibrium with an ACE-linked QTL. Linkage analysis with a highly informative polymorphism at the neighboring growth-hormone gene (GH) shows surprisingly little support for linkage (LOD score [Z] = 0.12). An extended analysis with a two-QTL model, where an ACE-linked QTL interacts additively with an unlinked QTL, significantly improves both the fit of the model (P = .002) and the support for linkage between the ACe-linked QTL interacts additively with an unlinked QTL, significantly improves both the fit of the model (P = .002) and the support for linkage between the ACe-linked QTL and GH polymorphism (Z = 5.0). We conclude that two QTLs jointly influence serum ACE levels in this population. One QTL is located within or close to the ACE locus and explains 27% of the total variability; the second QTL is unlinked to the ACE locus and explains 52% of the variability. The identification of the molecular mechanisms underlying both QTLs is necessary in order to interpret the role of ACE in cardiovascular disease.

Analysis of Variance↗
PubMed1996

Quantitative trait locus gene mapping: a new method for locating alcohol response genes.

Alcoholism is a multigenic trait with important non-genetic determinants. Studies with genetic animal models of susceptibility to several of alcohol's effects suggest that several genes contributing modest effects on susceptibility (Quantitative Trait Loci, or QTLs) are important. A new technique of QTL gene mapping has allowed the identification of the location in mouse genome of several such QTLs. The method is described, and the locations of QTLs affecting the acute alcohol withdrawal reaction are described as an example of the method. Verification of these QTLs in ancillary studies is described and the strengths, limitations, and future directions to be pursued are discussed. QTL mapping is a promising method for identifying genes in rodents with the hope of directly extrapolating the results to the human genome. This review is based on a paper presented at the First International Congress of the Latin American Society for Biomedical Research on Alcoholism, Santiago, Chile, November 1994.

Journal Article↗
PubMed1997

Mapping a quantitative trait locus involved in melanotic encapsulation of foreign bodies in the malaria vector, Anopheles gambiae.

A Plasmodium-refractory strain of Anopheles gambiae melanotically encapsulates many species of Plasmodium, whereas wild-type mosquitoes are usually susceptible. This encapsulation trait can also be observed by studying the response of refractory and susceptible strains to intrathoracically injected CM-Sephadex beads. We report the results of broad-scale quantitative trait locus (QTL) mapping of the encapsulation trait using the bead model system. Interval mapping using the method of maximum likelihood identified one major QTL, Pen1. The 13.7-cM interval containing Pen1 was defined by marker AGH157 at 8E and AGH46 at 7A on 2R. Pen1 was associated with a maximum LOD score of 9.0 and accounted for 44% of the phenotypic variance in the distribution of phenotypes in the backcross. To test if this QTL is important for encapsulation of Plasmodium berghei, F2 progeny were infected with P. berghei and evaluated for degree of parasite encapsulation. For each of the two markers that define the interval containing Pen1, a significant difference of encapsulation was seen in progeny with at least one refractory allele in contrast with homozygous susceptible progeny. These results suggest that Pen1 is important for melanotic encapsulation of Plasmodium as well as beads.

Animals↗
PubMed1992

P element transposition contributes substantial new variation for a quantitative trait in Drosophila melanogaster.

The P-M system of transposition in Drosophila melanogaster is a powerful mutator for many visible and lethal loci. Experiments using crosses between unrelated P and M stocks to assess the importance of transposition-mediated mutations affecting quantitative loci and response to selection have yielded unrepeatable or ambiguous results. In a different approach, we have used a P stock produced by microinjection of the ry506 M stock. Selection responses were compared between transposition lines that were initiated by crossing M strain females with males from the "co-isogenic" P strain, and ry506 M control lines. Unlike previous attempts to quantify the effects of P element transposition, there is no possibility of P transposition in the controls. During 10 generations of selection for the quantitative trait abdominal bristle number, none of the four control lines showed any response to selection, indicative of isogenicity for those loci affecting abdominal bristle number. In contrast, three of the four transposition lines showed substantial response, with regression of cumulative response on cumulative selection differential ranging from 15% to 25%. Transposition of P elements has produced new additive genetic variance at a rate which is more than 30 times greater than the rate expected from spontaneous mutation.

Animals↗
PubMed1996

Quantitative trait loci contributing to phencyclidine-induced and amphetamine-induced locomotor behavior in inbred mice.

Phencyclidine (PCP) and amphetamine (AMP) can induce psychotic syndromes in humans, whereas administration of these drugs to mice results in behavioral activation that is influenced by genetic factors. Quantitative trait loci (QTL) underlying genetic differences in response to PCP and AMP in mice were provisionally identified by correlating allelic variation at known marker loci in the BXD series of recombinant inbred (RI) mice and its progenitors (C57BL/6J and DBA/2J inbred strains) with the locomotor response of each strain to PCP and AMP. Total distance traveled for individual mice from each of the 26 BXD RI and two progenitor strains was measured after injections of normal saline and 7.5 mg/kg i.p. injection of PCP. This procedure was repeated after 1 week, using 5.0 mg/kg of AMP, instead of PCP. Markers significantly (p < .01) correlated with response to PCP map to murine chromosomes 1, 14, and 15. Response to amphetamine was correlated with markers mapping to chromosomes 4, 5, 6, 8, 14, and 18. Identification of the QTL underlying PCP-induced and AMP-induced behavior in mice may provide clues into the complicated genetics of psychosis in humans.

Amphetamine↗
PubMed1999

Sampling strategies for model free linkage analyses of quantitative traits: implications for sib pair studies of reading and spelling disabilities to minimize the total study cost.

One approach to establish linkage is based on allele sharing methods for sib pairs. In recent years the use of selected sib pairs to increase power for mapping quantitative traits in humans has been discussed intensively. In this paper the different basic principles for sib pair sampling proposed in the literature are made evident. Implications for ascertainment schemes of sib pairs to minimize the total study cost in linkage analyses on reading and spelling disabilities are discussed.

Child↗
PubMed1993

Microsatellite mapping of the gene causing weaver disease in cattle will allow the study of an associated quantitative trait locus.

A genetic disease in cattle, progressive degenerative myeloencephalopathy (weaver disease), is associated with increased milk production. This association could result from population stratification, from a pleiotropic effect of a single gene, or from linkage disequilibrium between the gene causing weaver disease and a quantitative trait locus (QTL) for milk production. To test these hypotheses, we performed an extensive linkage study in a bovine pedigree segregating for the weaver condition and identified a microsatellite locus (TGLA116) closely linked to the weaver gene (zmax, 8.15; theta, 0.03). TGLA116 and, by extension, the weaver locus were assigned to bovine synteny group 13. This microsatellite can be used to identify weaver carriers, to select against this genetic defect, and to study the effect of the corresponding chromosomal region on milk production in Brown Swiss and other breeds of cattle.

Animals↗
PubMed1996

Quantitative trait loci influencing cholesterol and phospholipid phenotypes map to chromosomes that contain genes regulating blood pressure in the spontaneously hypertensive rat.

The frequent coincidence of hypertension and dyslipidemia suggests that related genetic factors might underlie these common risk factors for cardiovascular disease. To investigate whether quantitative trait loci (QTLs) regulating lipid levels map to chromosomes known to contain genes regulating blood pressure, we used a genome scanning approach to map QTLs influencing cholesterol and phospholipid phenotypes in a large set of recombinant inbred strains and in congenic strains derived from the spontaneously hypertensive rat and normotensive Brown-Norway (BN.Lx) rat fed normal and high cholesterol diets. QTLs regulating lipid phenotypes were mapped by scanning the genome with 534 genetic markers. A significant relationship (P < 0.00006) was found between basal HDL2 cholesterol levels and the D19Mit2 marker on chromosome 19. Analysis of congenic strains of spontaneously hypertensive rat indicated that QTLs regulating postdietary lipid phenotypes exist also on chromosomes 8 and 20. Previous studies in the recombinant inbred and congenic strains have demonstrated the presence of blood pressure regulatory genes in corresponding segments of chromosomes 8, 19, and 20. These findings provide support for the hypothesis that blood pressure and certain lipid subfractions can be modulated by linked genes or perhaps even the same genes.

Animals↗
PubMed1994

Quantitative trait loci mapping of genes that influence the sensitivity and tolerance to ethanol-induced hypothermia in BXD recombinant inbred mice.

A recent method allows the identification of the rough genetic map location in mice of genes that exert modest effects on continuously distributed (i.e., quantitative) variables. Sensitivity and tolerance tolerance to the hypothermic effect of ethanol were studied with the purpose of identifying such quantitative trait loci (QTL). Mice from two progenitor inbred strains, C57BL/6J and DBA/2J, and 19 of their recombinant inbred (RI) BXD strains, were given ethanol daily for 3 days. By administering several doses of ethanol and recording multiple postdrug temperatures on the first and third injection day, the authors were able to compute several indices of initial sensitivity and tolerance magnitude in the RI strain battery. The strains differed at most times and doses in their acute reductions in body temperature with respect to their predrug base lines, which indicated genetic control of sensitivity to ethanol-induced hypothermia. The areas under the curve (which describes the initial hypothermic response over time), a measure that reflects both the maximal hypothermia achieved and the duration of total hypothermic response, also differed. The strains also differed in the magnitude of the tolerance developed to ethanol-induced hypothermia. Genetic determinants of sensitivity (and tolerance) to different doses of ethanol were primarily independent, although genetic sensitivity and tolerance to the intermediate (2- and 3-g/kg) doses were significantly correlated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Mapping quantitative trait loci for open-field behavior in mice.

By performing a whole genome screen in an F2 intercross of two strains of mice (A/J and C57BL/6J), which differ markedly in their behavioral response to a brightly lit open field (O-F), we have mapped several quantitative trait loci (QTL) for this complex behavioral phenotype. QTL on chromosomes 1 and 10 were identified that affect both initial ambulation in the O-F (initial "response to novelty" ambulation) (lod of 7.1 and 8.8, respectively) and vertical rearings (lod of 4.5 and 8.5, respectively). For habituated O-F behavior, QTL were identified on chromosomes 3 and 10 for ambulation (lod of 4.1 and 14.7, respectively) and on chromosomes 1, 10, and 19 for vertical rearings (lod of 5.8, 6.0, and 4.7, respectively). The QTL on chromosome 1 (near D1Mit116; 101 cM) was specific for initial O-F ambulation behavior, whereas the QTL on chromosome 10 (near D10Mit237; 74 cM) affected both initial and habituated rearing behavior. Additional suggestive QTL (lod, > 2.8) were mapped to chromosomes 1, 8, 11, 15, and 19. The QTL on chromosomes 1, 10, and 19 individually explain from 3.2 to 12.7%. Collectively, the multiple independent QTL explain from 16.3 to 24.1% of the F2 population's phenotypic variance, depending on the trait. These identified QTL should prove useful for dissecting the genetic and behavioral dimensions of O-F behavior, fostering an understanding of individual differences.

Animals↗
PubMed1995

Statistical validity for testing associations between genetic markers and quantitative traits in family data.

In genetic analysis it is often of interest to analyze associations between traits of unknown genetic etiology and genetic markers from pedigree data. Statistical methods that assume independence of pedigree members cannot be used because they disregard the statistical dependencies of members in a pedigree. For quantitative traits, a regression model proposed by George and Elston [Genet Epidemiol 4:193-201, 1987] uses an asymptotic likelihood ratio test and incorporates a correlation structure that allows for statistical dependence among the pedigree members. The statistical validity of this test is assessed for finite samples by measuring the discrepancy between the empirical and theoretical chi-square distributions. The variance of the mean of the dependent variable is determined to be related to this discrepancy and can be used to determine whether a pedigree structure is large enough for making valid statistical inferences on the basis of the asymptotic test. A multi-generational pedigree of 200 or so individuals should in many cases be sufficient for valid results when using the asymptotic likelihood ratio test for the association between markers and continuous traits.

Family↗
PubMed2002

Mapping of the QTL (quantitative trait locus) conferring partial resistance to leaf blast in rice cultivar Chubu 32.

The rice cultivar Chubu 32 possesses a high level of partial resistance to leaf blast. The number and chromosomal location of genes conferring this resistance were detected by restriction fragment length polymorphism (RFLP) linkage mapping and quantitative trait locus (QTL) analysis. For the mapping, 149 F(3) lines derived from the cross between rice cultivar Norin 29, with a low level of partial resistance, and Chubu 32 were used, and their partial resistance to leaf blast was assessed in upland nurseries. A linkage map covering six chromosomes and consisting of 36 RFLP markers was constructed. In the map, only one significant QTL (LOD>2.0) for partial resistance was detected on chromosome 11. This QTL explained 45.6% of the phenotypic variation. The segregation ratio of the F3 lines was 3:1 for partial resistance to susceptibility. These results suggest that the partial resistance in Chubu 32 is controlled by a major gene.

Journal Article↗
PubMed1996

Quantitative trait locus analyses of sleep-times induced by sedative-hypnotics in LSXSS recombinant inbred strains of mice.

The long-sleep (LS) and short-sleep (SS) selected lines of mice show highly significant differences in sleep-time for many sedative-hypnotic drugs, and the quantitative genetic nature of these differences has been well-established. Using an interval-mapping approach, quantitative trait locus (QTL) analyses of LSXSS recombinant inbred (RI) strains have been applied to sleep-time responses for various classes of sedative-hypnotic drugs: alcohols (ethanol, n-propanol, and n-butanol), the atypical anesthetic chloral hydrate, barbiturates (pentobarbital and secobarbital), and benzodiazepines (chlordiazepoxide and flurazepam). Several provisional QTLs were mapped to similar locations within and between drug classes, suggesting that some common loci are involved in sleep-times elicited by these drugs. Consistent with correlations of strain mean sleep-times between drugs tested in the LSXSS recombinant inbred strains, the number of provisional QTLs mapping to the locations of highest significance for ethanol decreases when the lipid solubility of a particular drug becomes less similar to that of ethanol. Provisional QTLs mapped for the benzodiazepines, however, revealed considerable overlap with those mapped for ethanol, although these drugs represented the most lipid-soluble category of sedative-hypnotics tested. Provisional QTLs for pentobarbital and secobarbital differed from most of those mapped for the alcohols, which supports the hypothesis that alcohols and barbiturates exert their effects mainly through different biological mechanisms in the LS and SS lines. Blood ethanol concentrations at regaining the righting reflex also mapped to several provisional QTLs corresponding to ethanol-induced sleep-times that support the contention that sleep-time is a reasonable index of the observed differences in central nervous system sensitivities to ethanol between LS and SS mice.

1-Butanol↗
PubMed2002

Quantitative Trait Loci Associated with Foliar Trigonelline Accumulation in Glycine Max L.

The objective of this study was to utilize a Glycine max RIL population to (1) evaluate foliar trigonelline (TRG) content in field-grown soybean, (2) determine the heritability of TRG accumulation, and (3) identify DNA markers linked to quantitative trait loci (QTLs) conditioning variation in TRG accumulation. Frequency distributions of 70 recombinant inbred lines showed statistically no significant departure from normality (P >.05) for TRG accumulation measured at pod development stage (R4). Six different molecular linkage groups (LGs) (B2, C2, D2, G, J, and K) were identified to be linked to QTLs for foliar TRG accumulation. Two unique microsatellite markers (SSR) on two different linkage groups identified QTL significantly associated with foliar TRG accumulation: a region on LG J (Satt285) (P =.0019, R(2) = 15.9%) and a second region on LG C2 (Satt079) (P =.0029, R(2) = 13.4%).

Journal Article↗
PubMed1975

H-2-associated quantitative traits; statistical analysis of the relative contributions of the H-2 linked genes and the residual genotype.

Several associations have been recently reported of the kind that a certain H-2 haplotype tends to be accompanied by a low value and another H-2 haplotype by a high value of some quantitative traits. This includes also the weights of lymphoid and reproductive organs. In order to throw more light on the seeming clustering within the H-2 gene complex of the genetic determinants of such traits, statistical analysis of the relative contributions of the H-2 and the total residual genotypes to the variations in the weight of the thymus, spleen, lymph nodes, testes, seminal vesicles and ovaries was performed. Ten genotypically uniform populations of 2-month-old mice, each consisting of 31 males and 31 females, were analyzed using two different statistical procedures. Four of them were mice of the inbred strains A (H-2a), B10 (H-2b), A.BY (H-2b) and B10.A (H-2a) and six were various F1 hybrids derived from these four strains. The conclusion based on both approaches was that the relative contribution to the variations in the weight of the tested organs from the H-2 haplotype is much smaller or maximally not greater than the contribution from the total residual genotype.

Animals↗
PubMed1995

Mapping of quantitative trait loci for blood pressure and cardiac mass in the rat by genome scanning of recombinant inbred strains.

In the HXB and BXH recombinant inbred strains derived from the spontaneously hypertensive rat and the normotensive Brown Norway rat, we determined the strain distribution patterns of 500 genetic markers to scan the rodent genome for quantitative trait loci regulating cardiac mass and blood pressure. The markers spanned approximately 1,139 cM of the genome and were tested for correlations with left ventricular mass adjusted for body weight, and with systolic, diastolic, and mean arterial pressures. The marker for the dopamine 1A receptor (Drd1a) on chromosome 17 showed the strongest correlation with left ventricular heart weight (P = .00038, r = -0.59) and the relationship to heart weight was independent of blood pressure. The markers showing the strongest correlations with systolic, diastolic, and mean arterial pressure were D19Mit7 on chromosome 19 (P = .0012, r = .55), D2N35 on chromosome 2 (P = .0008, r = .56), and Il6 on chromosome 4 (P = .0018, r = .53), respectively. These studies demonstrate that the HXB and BXH strains can be effectively used for genome scanning studies of complex traits and have revealed several chromosome regions that may be involved in the genetic control of blood pressure and cardiac mass in the rat.

Animals↗
PubMed1995

A brute force dichotomization approach to quantitative trait linkage analysis.

The effect of dichotomizing a continuous phenotype in linkage analysis of a simulated oligogenic trait is explored. We conclude that dichotomization does not in itself preclude the detection of loci which account for as little as 16% of the genetic variance of the disease. The effects of inclusion of known covariates and quantitative trait linkage analysis are also discussed.

Genetic Diseases, Inborn↗
PubMed1997

Confirmation of quantitative trait loci for ethanol sensitivity in long-sleep and short-sleep mice.

Initial insensitivity to alcohol is a strong predictor of human alcoholism, a widespread and heritable health problem. The Long Sleep and Short Sleep lines of mice were developed by genetic selection for high or low alcohol sensitivity. We have identified seven quantitative trait loci (QTLs) specifying differences in alcohol sensitivity using intercross progeny from these selected strains. These QTLs (Lorel-Lore7) together account for approximately 60% of the total genetic variance for this trait. This represents the first report of linkages for genes influencing alcohol action in any mammalian system using stringent, genome-wide mapping criteria.

Alcoholic Intoxication↗