Browsing by Author "Roodt-Wilding, R."

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    Evaluation of the OvineSNP50 chip for use in four South African sheep breeds : short communication
    (South African Society for Animal Science, 2016) Sandenbergh, L.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Roodt-Wilding, R.; Snyman, M. A.; Bester-Van Der Merwe, A. E.
    Relatively rapid and cost-effective genotyping using the OvineSNP50 chip holds great promise for the South African sheep industry and research partners. However, SNP ascertainment bias may influence inferences from the genotyping results of South African sheep breeds. Therefore, samples from Dorper, Namaqua Afrikaner (NA), South African Merino (SA Merino) and South African Mutton Merino (SAMM) were genotyped to determine the utility of the OvineSNP50 chip for these important South African sheep breeds. After quality control measures had been implemented, 85 SA Merino, 20 Dorper, 20 NA and 19 SAMM samples remained, with an average call rate of 99.72%. A total of 49 517 (91.30%) SNPs on the chip met quality control measures and were included in downstream analyses. The NA had the fewest polymorphic loci, 69.20%, while the SAMM, Dorper and SA Merino had between 81.16% and 86.85% polymorphic loci. Most loci of the SA Merino, Dorper and SAMM had a MAF greater than or equal to 0.3. In contrast, the NA exhibited a large number of rare alleles (MAF < 0.1) and a uniform distribution of other loci across the MAF range (0.1 < MAF ≤ 0.5). The NA exhibited the least genetic diversity and had the greatest inbreeding coefficient among the four breeds. The results of the Dorper, SA Merino, and SAMM compare favourably with those of international breeds and thus demonstrate the utility of the OvineSNP50 chip for these breeds. Effects of SNP ascertainment bias, however, could be seen in the number of non-polymorphic loci and MAF distribution of the three commercial breeds in comparison with those of the NA. The implementation of methods to reduce the effect of SNP ascertainment bias and to ensure unbiased interpretation of genotype results should therefore be considered for future studies using OvineSNP50 chip genotype results.
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    Isolation and validation of microsatellite markers from a depleted South African sciaenid species, the dusky kob (Argyrosomus japonicus), by means of the FIASCO/454 approach
    (Springer Verlag, 2013-04) Mirimin, L.; Ruiz Guajardo, J. C.; Vervalle, J.; Bester-Van der Merwe, Aletta; Kerwath, S.; Macey, B.; Bloomer, P.; Roodt-Wilding, R.
    The dusky kob (Argyrosomus japonicus) is a large, estuarine-dependent sciaenid fish that has been severely depleted in South African waters and that, in recent years, has received considerable attention from the local fish farming industry. Discovery and application of appropriate molecular markers is necessary to improve the understanding of wild population structure, assist the effectiveness of broodstock and breeding programmes, and ensure monitoring of potential interactions between wild and farmed fish. The present study uses a recently tested approach that combines the FIASCO enrichment protocol with 454 GS-FLX Next Generation Sequencing, to identify large numbers of microsatellite-containing sequences at a low cost and high discovery rate from the dusky kob genome. Following the FIASCO enrichment (targeting specifically tetranucleotide repeats), 2,355 potential tetranucleotide microsatellites (perfect repeat motifs including eight or more repeat units flanked by regions for primer design) were identified from 1/5th of a single 454 lane. From these sequences, a test panel of 60 potential markers was selected for validation. A total of eight (13 %) markers were successfully amplified from a test sample of wild dusky kob individuals and showed high levels of polymorphism (observed heterozygosity per locus ranging between 0.375 and 0.905). Cross-species amplification of seven of these markers was also successfully carried out in another closely related and commercially important South African sciaenid species, the silver kob (A. inodorus). The microsatellite markers developed in the present study are readily available tools suitable to address genetic variability of Argyrosomus species of southern Africa.
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    Molecular markers to assist the South African abalone industry
    (Academy of Science for South Africa, 2006) Roodt-Wilding, R.; Slabbert, Ruhan
    HALIOTIS MIDAE (PERLEMOEN) IS THE ONLY southern African species of abalone to be commercially exploited. Commercial farms are currently producing 750 tons per annum, making this an economically viable enterprise. Increasing world demand and dwindling natural populations have, however, necessitated the adoption of genetic management practices on South African abalone farms to remain sustainable. This can be done by means of DNA markers, which are employed to investigate various phenomena from genetic diversity, parentage and broodstock contributions to linkage mapping and marker-assisted selection for genetic enhancement of the commercial species. The use of microsatellite markers for various abalone aquaculture applications is highlighted in this review.
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    Resprouters versus reseeders : are wild rooibos ecotypes genetically distinct?
    (Frontiers, 2021-12-20) Brooks, J.; Makunga, N. P.; Hull, K. L.; Brink-Hull, M.; Malgas, R.; Roodt-Wilding, R.; Dlamini, Zodwa
    Aspalathus linearis (Burm. F.) R. Dahlgren (Fabaceae) or rooibos, is a strict endemic species, limited to areas of the Cederberg (Western Cape) and the southern Bokkeveld plateau (Northern Cape) in the greater Cape Floristic Region (CFR) of South Africa. Wild rooibos, unlike the cultivated type, is variable in morphology, biochemistry, ecology and genetics, and these ecotypes are broadly distinguished into two main groups, namely, reseeders and resprouters, based on their fire-survival strategy. No previous assessment of genetic diversity or population structure using microsatellite markers has been conducted in A. linearis. This study aimed to test the hypothesis that wild rooibos ecotypes are distinct in genetic variability and that the ecotypes found in the Northern Cape are differentiated from those in the Cederberg that may be linked to a fire-survival strategy as well as distinct morphological and phytochemical differences. A phylogeographical and population genetic analyses of both chloroplast (trnLF intergenic region) and newly developed species-specific nuclear markers (microsatellites) was performed on six geographically representative wild rooibos populations. From the diversity indices, it was evident that the wild rooibos populations have low-to-moderate genetic diversity (He: 0.618–0.723; Ho: 0.528–0.704). The Jamaka population (Cederberg, Western Cape) had the lowest haplotype diversity (H = 0.286), and the lowest nucleotide diversity (π = 0.006) even though the data revealed large variations in haplotype diversity (h = 0.286–0.900) and nucleotide diversity (π = 0.006–0.025) between populations and amongst regions where wild rooibos populations are found. Our data suggests that populations of rooibos become less diverse from the Melkkraal population (Suid Bokkeveld, Northern Cape) down towards the Cederberg (Western Cape) populations, possibly indicative of clinal variation. The largest genetic differentiation was between Heuningvlei (Cederberg, Western Cape) and Jamaka (FST = 0.101) localities within the Cederberg mountainous region, and, Blomfontein (Northern Cape) and Jamaka (Cederberg) (FST = 0.101). There was also a significant isolation by distance (R2 = 0.296, p = 0.044). The presence of three main clusters is also clearly reflected in the discriminant analysis of principal components (DAPC) based on the microsatellite marker analyses. The correct and appropriate management of wild genetic resources of the species is urgently needed, considering that the wild Cederberg populations are genetically distinct from the wild Northern Cape plants and are delineated in accordance with ecological functional traits of reseeding or resprouting, respectively. The haplotype divergence of the ecotypes has also provided insights into the genetic history of these populations and highlighted the need for the establishment of appropriate conservation strategies for the protection of wild ecotypes.