The first chapter gives an overall introduction to Arachis hypogaea L., the crop that was studied in this thesis. The literature reviewed touched on various aspects of the crop in general such as the importance of peanut as a crop, its botanical description, origin and distribution world-wide. Different marker studies done on A. hypogaea L. and their extents have also been reviewed. The chapter also looked at the oryzacystatin-1 (OC-1) gene as a possible candidate gene for peanut improvement in South Africa (Chapter I). Agronomic data was collected in an attempt to observe and evaluate variability amongst the 18 commercially cultivated peanut lines from South Africa. The growth habits, growth seasons, testa colours, total oil percentages and oleic and linoleic acid ratios were the agronomic characters used to study variation (Chapter II). One South African commercially cultivated peanut line, JL 24, was transformed with the oryzacystatin-1 (OC-1) gene, which was isolated from rice. Three to four week old plantlets were vacuum infiltrated with Agrobacterium during the transformation process and various methods were used to analyze the putative transformants (Chapter III). Two types of DNA markers along with phynotypic data were used to examine polymorphism among 18 South African peanut lines and a transformed line. The amplified fragment length polymorphisms (AFLPs) and simple sequences repeats (SSRs) were the two DNA markers used in this study to determine the level of variation amongst these lines (Chapter IV).