Linkage disequilibrium fine mapping of quantitative trait loci: A simulation study

Recently, the use of linkage disequilibrium (LD) to locate genes which affect quantitative traits (QTL) has received an increasing interest, but the plausibility of fine mapping using linkage disequilibrium techniques for QTL has not been well studied. The main objectives of this work were to (1) measure the extent and pattern of LD between a putative QTL and nearby markers in finite populations and (2) investigate the usefulness of LD in fine mapping QTL in simulated populations using a dense map of multiallelic or biallelic marker loci. The test of association between a marker and QTL and the power of the test were calculated based on single-marker regression analysis. The results show the presence of substantial linkage disequilibrium with closely linked marker loci after 100 to 200 generations of random mating. Although the power to test the association with a frequent QTL of large effect was satisfactory, the power was low for the QTL with a small effect and/or low frequency. More powerful, multi-locus methods may be required to map low frequent QTL with small genetic effects, as well as combining both linkage and linkage disequilibrium information. The results also showed that multiallelic markers are more useful than biallelic markers to detect linkage disequilibrium and association at an equal distance

nBu2Sn(SnBu)2 and nBu3SnEnBu (E = S or Se) - effective single source precursors for the CVD of SnS and SnSe thermoelectric thin films

The use of single source precursors offers a convenient option for the chemical vapour deposition of thin film semiconductor materials with good stoichiometric control and precursor efficiency. Here we show that reaction of nBu3SnCl with NaSnBu or LiSenBu, or nBu2SnCl2 with 2 mol equiv. of NaSnBu, gives the molecular alkyltin chalcogenolate precursors, nBu3SnEnBu (E = S (1), Se (3)) and nBu2Sn(SnBu)2 (2), respectively, in good yield as colourless (S) or yellow/orange (Se) oils. These were characterised by 1H, 13C{1H}, 77Se{1H} and 119Sn{1H} NMR spectroscopy, microanalysis and thermogravimetric analysis. Low pressure CVD experiments using these precursors showed that (1) gave S-deficient SnS thin films, whereas using (2) and implementing short deposition times and low precursor loadings, gave stoichiometric SnS films. Stoichiometric SnSe films were also obtained using (3) and confirmed by grazing incidence XRD analysis, which revealed the films adopt the orthorhombic Pnma structure. SEM and EDX analysis, together with Raman spectroscopic data, were also used to identify the films deposited and to correlate with the deposition conditions employed. Variable temperature Seebeck and Hall effect characterisation confirm that the stoichiometric SnS and SnSe films are semiconducting and highly resistive, giving large positive Seebeck coefficients, with the overall power factor ranging from 0.017 at 300 K to 0.049 μW cm−1 K−2 at 450 K for SnS and increasing from 0.06 at 300 K to 0.4 μW cm−1 K−2 at 425 K for SnSe