Confirmation of linkage between the loci for HL-A and glyoxalase I

Summary Linkage analysis of 7 families with 30 children confirmed previous findings of the linkage between HL-A and GLO. Out of 28 families with 90 children the highest lod score value obtained was +8.887 (recombination fraction=0.1).Supported by the Deutsche Forschungsgemeinschaft.     

Probable genetic linkage between a locus for human urinary pepsinogen and the HL-A loci.

The genetic basis of familial variation in the relative intensities of human urinary pepsinogen isozymes is not completely clear from family studies. An investigation of the linkage relationships of pepsinogen isozyme 5, considering only segregation for the presence or absence of Pg 5, yields a peak lod score of 4.1 at theta = .1 for linkage with HL-A1 or HL-A2. Added to data from segregation interpreted according to a scheme proposed for the inheritance of intensity differences in Pg 5, the peak lod score becomes 3.0 at theta = .2. Data derived from the segregation of pepsinogen isozyme 4, possibly determined by an allele to that controlling the presence or absence of Pg 5, further reduces the total lod score at theta = .2 to 2.9. The results indicate probable linkage between a locus for urinary pepsinogen and the HL-A loci, but are insufficient to permit any conclusion concerning possible heterogeneity in the linkage relationships of Pg 4 and Pg 5 to HL-A.     

No evidence for linkage between the loci for coagulation factor XIII-A and HLA

Summary The linkage analysis between the locus for coagulation factor XIII-A (F13A) and HLA region genes (HLA-A,-C,-B) was performed. In males, the maximum of lod scores between F13A and HLA was 0.33 at =0.30, and in females lod scores were negative at all values of . The results provided no evidence for close linkage between F13A and HLA genes.     

Possible linkage of HL-A and GLO

Summary In 21 informative families with 60 children, a possible linkage between HL-A and GLO was found (recombination fraction approximatively 0.15). The sequence of the loci on chromosome 6 might be GLO, HL-A, PGM₃, MNSs.

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Zusammenfassung Koppelungsuntersuchungen bei 21 informativen Familien mit 60 Kindern zeigten, daß die Loci HL-A und GLO möglicherweise gekoppelt sind (Rekombinationsfrequenz ca. 15%). Die Reihenfolge der Loci am Chromosom 6 kann wie folgt angenommen werden: GLO, HL-A, PGM₃, MNSs.

     

Sex differences in linkage between autosomal loci

In the case of conventional selection theory with multiplicative gene action between loci and no sex differences except in crossover frequencies, it is shown that the usual conditions for stability hold when the mean of the recombination frequencies for the two sexes is used. For additive gene action between loci, it is shown that, after one generation of random mating, the gene frequencies of male and female origin are the same. This equality implies the nondecreasing property of the mean fitness function. Some attention is also given to neutral loci.     

Sequential sampling in determining linkage between marker loci and quantitative trait loci

Summary As compared to classical, fixed sample size techniques, simulation studies showed that a proposed sequential sampling procedure can provide a substantial decrease (up to 50%, in some cases) in the mean sample size required for the detection of linkage between marker loci and quantitative trait loci. Sequential sampling with truncation set at the required sample size for the non-sequential test, produced a modest further decrease in mean sample size, accompanied by a modest increase in error probabilities. Sequential sampling with observations taken in groups produced a noticeable increase in mean sample size, with a considerable decrease in error probabilities, as compared to straightforward sequential sampling. It is concluded that sequential sampling has a particularly useful application to experiments aimed at investigating the genetics of differences between lines or strains that differ in some single outstanding trait.     

Confirmation of the linkage HL-A/PGM3.

In a series of 42 families with 101 children the linkage between HL-A and PGM3 could be confirmed (most likely recombination fraction for male equals 0.15).     

Detection of linkage between marker loci and loci affecting quantitative traits in crosses between segregating populations

Summary By making use of pedigree information and information on marker-genotypes of the parent and F-1 individuals crossed to form an F-2 population, it is possible to carry out a linkage analysis between marker loci and loci affecting quantitative traits in a cross between segregating parent populations that are at fixation for alternative alleles at the QTL, but share the same alleles at the marker loci. For two-allele systems, depending on marker allele frequencies in the parent populations, 2–4 times as many F-2 offspring will have to be raised and scored for markers and quantitative traits in order to provide power equivalent to that obtained in a cross between fully inbred lines. Major savings in number of F-2 offspring raised can be achieved by scoring each parent pair for a large number of markers in each chromosomal region and scoring F-1 and F-2 offspring only for those markers for which the parents were homozygous for alternative alleles. For multiple allele systems, particularly when dealing with hypervariable loci, only 10%–20% additional F-2 offspring will have to be raised and scored to provide power equivalent to that obtained in a cross between inbred lines. When a resource population contains novel favorable alleles at quantitative trait loci that are not present (or rare) in a commercial population, analyses of this sort will enable the loci of interest to be identified, mapped and manipulated effectively in breeding programs.Contribution no. 2124-E, 1987 series from The Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel     

Optimum spacing of genetic markers for determining linkage between marker loci and quantitative trait loci

The cost of experiments aimed at determining linkage between marker loci and quantitative trait loci (QTL) was investigated as a function of marker spacing and number of individuals scored. It was found that for a variety of experimental designs, fairly wide marker spacings (ca. 50 cM) are optimum or close to optimum for initial studies of marker-QTL linkage, in the sense of minimizing overall cost of the experiment. Thus, even when large numbers of more or less evenly spaced markers are available, it will not always be cost effective to make full utilization of this capacity. This is particularly true when costs of rearing and trait evaluation per individual scored are low, as when marker data are obtained on individuals raised and evaluated for quantitative traits as part of existing programs. When costs of rearing and trait evaluation per individual scored are high, however, as in human family data collection carried out primarily for subsequent marker — QTL analyses, or when plants or animals are raised specifically for purposes of marker — QTL linkage experiments, optimum spacing may be rather narrow. It is noteworthy that when marginal costs of additional markers or individuals are constant, total resources allocated to a given experiment will determine total number of individuals sampled, but not the optimal marker spacing.     

Sample sizes required to detect linkage disequilibrium between two or three loci.

Estimates of the degree of nonrandom association among genes (linkage disequilibrium) can provide evidence of the role of natural selection in maintaining allozyme polymorphisms in natural populations. This paper outlines the maximum likelihood procedures for such estimates based on gametic or zygotic frequencies at the level of two loci. The analysis is extended to estimating disequilibrium between three loci. In particular, the question of the sampling requirements to detect different intensities of disequilibrium is considered. It is found that relatively large samples are required to detect nonrandom association, unless gene frequencies are intermediate and disequilibrium is relatively intense. This might be one reason why cases of linkage disequilibrium have so far proved to be the exception, rather than the rule, in population studies.     

Bayesian analysis of linkage between genetic markers and quantitative trait loci. I. Prior knowledge

Summary Prior information on gene effects at individual quantitative trait loci (QTL) and on recombination rates between marker loci and QTL is derived. The prior distribution of QTL gene effects is assumed to be exponential with major effects less likely than minor ones. The prior probability of linkage between a marker and another single locus is a function of the number and length of chromosomes, and of the map function relating recombination rate to genetic distance among loci. The prior probability of linkage between a marker locus and a quantitative trait depends additionally on the number of detectable QTL, which may be determined from total additive genetic variance and minimum detectable QTL effect. The use of this prior information should improve linkage tests and estimates of QTL effects.     

Close linkage between the albumin and Gc loci in the horse

Evidence for close linkage between the structural loci for albumin and Gc protein in the horse was presented. A recombination frequency (c) of 0.009 ± 0.006 (95 % confidence limits: 0.001 < c < 0.032) was estimated. These results were based on a study of a large sire family comprising 223 offspring from informative matings. No evidence of linkage disequilibrium was observed in one horse population studied.