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| Untersuchte Arbeit: Seite: 21, Zeilen: 1 ff. (komplett) |
Quelle: Mohamed 2009 Seite(n): 23 f., Zeilen: 3 ff.; 24: 4 ff. |
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| [Due to the out-breeding character of this species, LD extends only over a few kb and thus leads to] a high genetic resolution, up to the level of individual candidate genes that can be associated with a given trait (Rafalski and Morgante 2004, Gupta et al. 2005).
A European germplasm collection of 146 two-rowed spring barley cultivars was used to carry out LD mapping of yield traits using 236 AFLP markers (Kraakman et al. 2004). Associated markers were identified that are located in similar regions where QTLs for yield had been found in barley (Romagosa et al. 1999 and Li et al. 2006). A survey of 953 cultivated barley accessions representing a broad spectrum of the genetic diversity in barley genetic resources revealed that LD extends up to 50 cM but is highly dependent on population structure (Kraakman et al. 2004 and Malysheva-Otto et al. 2006). On the one hand, the high level of LD in barley is due to the inbreeding mating type of this species; on the other hand, the selection of germplasm plays an important role analysis of a germplasm collection of European cultivars, land races and wild barley accession from the Fertile Crescent region provided hints that the level of LD increases from cultivars to landraces to wild barley (Caldwell et al. 2006). Similarly, Morell et al. (2005) reported low levels of LD in wild barley by examining LD within and between 18 genes from 25 accessions. The genotyping database for 953 cultivated barley accessions profiled with 48 SSR markers was established. The principal coordinate analysis revealed structuring of the barley population with regard to (i) geographical regions and (ii) agronomic traits. Geographic origin contributed most to the observed molecular diversity. Genome-wide linkage disequilibrium (LD) was estimated as squared correlation of allele frequencies (r2). The values of LD for barley were comparable to other plant species (conifers, poplar and maize). The pattern of intrachromosomal LD with distances between the genomic loci ranging from 1 to 150 cM revealed that in barley LD extended up to distances as long as 50 cM with r2 > 0.05, or up to 10 cM with r2 > 0.2. Few loci mapping to different chromosomes showed significant LD with r2 > 0.05. The number of loci in significant LD as well as the pattern of LD was clearly dependent on the population structure. The LD in homogenous group of 207 European 2-rowed spring barleys compared to the highly structured worldwide barley population was increased in the number of loci pairs with r2 > 0.05 and had higher values of r2, although the percentage of intrachromosomal loci pairs in significant LD based on P < 0.001 was 100% in the whole set of varieties, but only 45% in the subgroup of European 2-rowed spring barley. The value of LD also varied depending on polymorphism of the loci selected for genotyping (Malysheva-Otto et al. 2006). |
Due to the out-breeding character of this species, LD extends only over a few kb and thus leads to a high genetic resolution, up to the level of individual candidate genes that can be associated with a given trait (Rafalski and Morgante 2004, Gupta et al. 2005).
[...] A European germplasm collection of 146 tworowed spring barley cultivars was used to carry out LD mapping of yield traits using 236 AFLP markers (Kraakman et al. 2004). Associated markers were identified that are located in similar regions where QTLs for yield had been found in barley. (Romagosa et al. 1999 and Li et al. 2006). A systematic survey of 953 gene bank accessions representing a broad spectrum of the genetic diversity in barley genetic resources revealed that LD extends up to 50 cM but is highly dependent on population structure (Kraakman et al. 2004 and Malysheva- Otto et al. 2006). On the one hand, the high level of LD in barley is due to the inbreeding mating type of this species; on the other hand, the selection of germplasm plays an important role Analysis of a germplasm collection of European cultivars, land races and wild barley accession from the Fertile Crescent region provided hints that the level of LD increases from cultivars to landraces to wild barley (Caldwell et al. 2006). Similarly, Morell et al. (2005) reported low levels of LD in wild barley by examining LD within and between 18 genes from 25 accessions. The genotyping database for 953 cultivated barley accessions profiled with 48 SSR markers was established. The PCoA revealed structuring of the barley population with regard to (i) geographical regions and (ii) agronomic traits. Geographic origin contributed most to the observed molecular diversity. Genome-wide linkage disequilibrium (LD) was estimated as squared correlation of allele frequencies (r2). The values of LD for barley were comparable to other plant species (conifers, poplar and maize). The pattern of intrachromosomal LD with distances between the genomic loci ranging from 1 to 150 cM revealed that in barley LD extended up to distances as long as 50 cM with r2 > 0.05, or up to 10 cM with r2 > 0.2. Few loci mapping to different chromosomes showed significant LD with r2 > 0.05. The number of loci in significant LD as well as the pattern of LD was clearly dependent on the population structure. The LD in the homogenous group of 207 European 2-rowed spring barleys compared to the highly structured worldwide barley population was increased in the number of loci pairs with r2 > 0.05 and had higher values of r2, although the percentage of intrachromosomal loci pairs in significant LD based on P < 0.001 was 100% in the whole set of varieties, but only 45% in the subgroup of European 2-rowed spring barleys (Malysheva-Otto et al. 2006). |
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