• International Journal of Industrial Entomology and Biomaterials
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• v.20 no.2
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• pp.37-43
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• 2010

The wild silkworm, Antheraea mylitta Drury (Lepidoptera: Saturniidae) is a polyphagous silk producing insect that feeds on Terminalia arjuna, T. tomentosa and Shorea robusta and is distributed in the forest belts in different states of India. Phenotypically distinct populations of the A. mylitta are called "eco-race" or "ecotypes". Genetic improvement of this wild silkworm has not progressed much due to lack of adequate information on the factors that control the expression of most of the economically important traits. Considering the amazing technological advances taking place in molecular biology, it is envisaged that it is now possible to take greater control on these intractable traits if a combination of genetic, molecular and bioinformatics tools are used. Linkage disequilibrium (LD) mapping is one such approach that has extensively been used in both animal and plant system to identify quantitative trait loci (QTLs) for a number of economically important traits. LD mapping has a number of advantages over conventional biparental linkage mapping. Therefore, LD mapping is considered more efficient for gene discovery to meet the challenge of connecting sequence diversity with heritable phenotypic differences. However, care must be taken to avoid detection of spurious associations which may occur due to population structure and variety interrelationships. In this review, we discuss how LD mapping is suitable for the dissection of complex traits in wild silkworms (Antheraea mylitta).

• Asian-Australasian Journal of Animal Sciences
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• v.14 no.3
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• pp.302-306
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• 2001

This study was carried out to construct mapping population and to evaluate the methods involved, including polymorphic DNA marker system and appropriate statistical analysis. As an initial step to establish chicken genome mapping project, White Leghorn (WL) and Korean Ogol chicken (KOC) were used for generating backcross population. From 8 initial parents, total 280 backcross progenies were obtained and 40 were used for genotyping and linkage analysis. For development of novel polymorphic markers for KOC, Random Amplified Polymorphic DNA (RAPD) markers specific for this chicken line were generated. Also included in this study were six microsatellite markers from East Lansing map as reference loci. For segregation analysis, 15 RAPD markers and 6 microsatellites were used to genotype the backcross population. Among the RAPD markers that we developed, 2 pairs of markers were identified to be linked and another 4 RAPD markers showed linkage with microsatellites of known map. In summary, this study showed that our backcross population generated from the mating of KOC to WL serves as a valuable genetic resource for genotyping. Furthermore, RAPD markers are proved to be valuable in linkage mapping analysis.

• Asian-Australasian Journal of Animal Sciences
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• v.25 no.1
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• pp.17-21
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• 2012

The purpose of this study was to improve mapping power and resolution for the QTL influencing carcass quality in Hanwoo, which was previously detected on the bovine chromosome (BTA) 6. A sample of 427 steers were chosen, which were the progeny from 45 Korean proven sires in the Hanwoo Improvement Center, Seosan, Korea. The samples were genotyped with the set of 2,535 SNPs on BTA6 that were imbedded in the Illumina bovine 50 k chip. A linkage disequilibrium variance component mapping (LDVCM) method, which exploited both linkage between sires and their steers and population-wide linkage disequilibrium, was applied to detect QTL for four carcass quality traits. Fifteen QTL were detected at 0.1% comparison-wise level, for which five, three, five, and two QTL were associated with carcass weight (CWT), backfat thickness (BFT), longissimus dorsi muscle area (LMA), and marbling score (Marb), respectively. The number of QTL was greater compared with our previous results, in which twelve QTL for carcass quality were detected on the BTA6 in the same population by applying other linkage disequilibrium mapping approaches. One QTL for LMA was detected on the distal region (110,285,672 to 110,633,096 bp) with the most significant evidence for linkage (p< $10^{-5}$). Another QTL that was detected on the proximal region (33,596,515 to 33,897,434 bp) was pleiotrophic, i.e. influencing CWT, BFT, and LMA. Our results suggest that the LDVCM is a good alternative method for QTL fine-mapping in detection and characterization of QTL.

• Asian Journal of Turfgrass Science
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• v.22 no.1
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• pp.85-100
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• 2008

Gray leaf spot (GLS) is a serious fungal disease caused by Pyricularia oryzae Cavara, recently reported on the important turf and forage species, perennial ryegrass (Lolium perenneL.). This fungus also causes rice blast, which is usually controlled by host resistance, but durability of resistance is a problem. Few instances of GLS resistance have been reported in perennial ryegrass. However, two major QTL for GLS resistance have been detected on linkage groups 3 and 6 in an Italian x perennial ryegrass mapping population. To confirm that those QTL are still detectable in the next generation and can function in a different genetic background, a resistant segregant from this population has been crossed with an unrelated susceptible perennial clone, to form a new mapping population segregating for GLS resistance. QTL analysis has been performed in the new population, using two different ryegrass field isolates and RAPD, RFLP, and SSR marker-based linkage maps for each parent. Results indicate the previously identified QTL on linkage group 3 is still significant in the new population, with LOD and percent of phenotypic variance explained ranging from 2.0 to 3.5 and 5% to 10%, respectively. Also two QTL were detected in the susceptible parent, with similar LOD and phenotypic variance explained. Although the linkage group 6 QTL was not detected, the major QTL on linkage group 3 appears to beconfirmed. These results will add to our understanding of the genetic architecture of GLS resistance in ryegrass, which will facilitate its use in perennial ryegrass breeding programs.

• Asian-Australasian Journal of Animal Sciences
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• v.19 no.12
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• pp.1702-1705
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• 2006

A simulation study was conducted to evaluate a fine-mapping method exploiting population-wide linkage disequilibrium. Data were simulated according to the pedigree structure based on a large paternal half-sib family population with a total of 1,034 or 2,068 progeny. Twenty autosomes of 100 cM were generated with 5 cM or 1 cM marker intervals for all founder individuals in the pedigree, and marker alleles and a number of quantitative trait loci (QTL) explaining a total of 70% phenotypic variance were generated and randomly assigned across the whole chromosomes, assuming linkage equilibrium between the markers. The founder chromosomes were then descended through the pedigree to the current offspring generation, including recombinants that were generated by recombination between adjacent markers. Power to detect QTL was high for the QTL with at least moderate size, which was more pronounced with larger sample size and denser marker map. However, sample size contributed much more significantly to power to detect QTL than map density to the precise estimate of QTL position. No QTL was detected on the test chromosomes in which QTL was not assigned, which did not allow detection of false positive QTL. For the multiple QTL that were closely located, the estimates of the QTL positions were biased, except when the QTL were located on the right marker positions. Our fine mapping simulation results indicate that construction of dense maps and large sample size is needed to increase power to detect QTL and mapping precision for QTL position.

• Asian-Australasian Journal of Animal Sciences
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• v.14 no.4
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• pp.587-596
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• 2001

In the last decade, rapid developments in molecular biotechnology and of genomic tools have enabled the creation of dense linkage maps across whole genomes of human, plant and animals. Successful development and implementation of interval mapping methodologies have allowed detection of the quantitative trait loci (QTL) responsible for economically important traits in experimental and commercial livestock populations. The candidate gene approach can be used in any general population with the availability of a large resource of candidate genes from the human or rodent genomes using comparative maps, and the validated candidate genes can be directly applied to commercial breeds. For the QTL detected from primary genome scans, two incipient fine mapping approaches are applied by generating new recombinants over several generations or utilizing historical recombinants with identity-by-descent (IBD) and linkage disequilibrium (LD) mapping. The high resolution definition of QTL position from fine mapping will allow the more efficient implementation of breeding programs such as marker-assisted selection (MAS) or marker-assisted introgression (MAI), and will provide a route toward cloning the QTL.

• Asian-Australasian Journal of Animal Sciences
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• v.15 no.9
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• pp.1250-1256
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• 2002

A novel fine-mapping method exploiting linkage disequilibrium (LD) was applied to better refine the quantitative trait loci (QTL) positions for milk production traits on bovine chromosome 14 in the pedigree comprising 22 paternal half-sib families of a Black-and-White Holstein-Friesian grand-daughter design in the Netherlands for a total of 1,034 sons. The chromosome map was constructed with the 31 genetic markers spanning 90 Kosambi cM with the average inter-marker distance of 3.5 cM. The linkage analyses, in which the effects of sire QTL alleles were assumed random and the random factor of the QTL allelic effects was incorporated into the Animal Model, found the QTL for milk, fat, and protein yield and fat and protein % with the Lod scores of 10.9, 2.3, 6.0, 25.4 and 3.2, respectively. The joint analyses including LD information by use of multi-marker haplotypes highly increased the evidence of the QTL (Lod scores were 25.1, 20.9, 11.0, 85.7 and 17.4 for the corresponding traits, respectively). The joint analyses including DGAT markers in the defined haplotypes again increased the QTL evidence and the most likely QTL positions for the five traits coincided with the position of the DGAT gene, supporting the hypothesis of the direct causal involvement of the DGAT gene. This study strongly indicates that the exploitation of LD information will allow additional gains of power and precision in finding and localising QTL of interest in livestock species, on the condition of high marker density around the QTL region.

• Asian-Australasian Journal of Animal Sciences
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• v.17 no.3
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• pp.309-312
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• 2004

We performed exon trapping in order to locate functional genes on chicken chromosomes (GGA) and to identify functional gene sequences from chicken cosmids. Sequence analysis of 100 clones revealed 17 putative exons, five of which were identified with known sequences in a gene database search: thymopoietin beta (TMPO), U5 snRNP-specific 40 kDa protein (HPRP8BP), dihydropyridine receptor alpha 1 subunit (CACNL1A3), cystein string protein (CPS) and C15orf4. We attempted to map the genes to chicken chromosomes by using FISH and linkage analysis. The chromosomal localizations were GGA1 (TMPO), GGA10 (C15orf4), GGA23 (HPRP8BP) and GGA28 (CPS) by FISH and linkage analysis, while that of CACNL1A3 was predicted to be on a microchromosome by FISH but not by linkage analysis. Comparative mapping analyses between chickens and humans for the genes revealed both known and new synteny. The syntenic conservation between GGA1 and human chromosome (HSA) 12q23 (TMPO) and between GGA10 and HSA15q25 (C15orf4), were consistent with a recent publication, while two new syntenies were observed between GGA28 and HSA20q13.3 in CPS and between GGA23 and HSA1p34-35 in HPRP8BP. The information of presently mapped genes can contribute as anchor markers based on functional genes and the construction of a comparative map.

• Asian-Australasian Journal of Animal Sciences
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• v.16 no.10
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• pp.1402-1405
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• 2003

The QTL(quantitative traits loci) linkage mapping of Hanwoo (Korean Cattle) chromosome 6 for daily gain and marbling score was performed using 378 individuals from 18 paternal half-sib families in Hanwoo. Hanwoo chromosome 6 were mapped to total length of 394.2 cM between 28 microsatellite loci using 36 microsatellite primers of BTA 6 linkage group. The QTL analysis for daily gain in Hanwoo showed 8 microsatellite loci (BM3026-5.66, EL03-5.58, BM4311-5.29, ILSTS035-4.50, BMS1242-4.37, BM1329-3.67, BM415-3.11, BMS2460-3.03) in larger than LOD score 3.0. Based on the QTL analysis for marbling score, LOD scores of 12 microsatellite loci (BM415-8.88, BM3026-7.15, ILSTS093-5.45, ILSTS035-4.91, EL03-4.69, BMS690-4.52, BM1329-4.43, BMS511-3.74, BMS1242-3.66, BMS518-3.65, BM4311-3.41, BMC4203-3.36) were found larger than 3.0.

• BMB Reports
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• v.35 no.5
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• pp.465-471
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• 2002

From fruiting bodies of L. edodes strain L-54, single-spore isolates (SSIs) were collected. Two parental types of L-54 were regenerated via monokaryotization. By means of random-amplified polymorphic DNA (RAPD), DNA samples from L-54, its two parental types, and 32 SSIs were amplified with arbitrary primers. Dedikaryotization was demonstrated, and 91 RAPD-based molecular markers were generated. RAPD markers that were segregated at a 1:1 ratio were used to construct a linkage map of L. edodes. This RAPD-linkage map greatly enhanced the mapping of other inheritable and stable markers [such as those that are linked to a phenotype (the mating type), a known gene (priA) and a sequenced DNA fragment (MAT)] with the aid of mating tests, bulked-segregant analysis, and PCR-single-strand conformational polymorphism. These markers comprised a genetic map of L. edodes with 14 linkage groups and a total length of 622.4 cM.