A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016. / The Organic Cation Transporter 2 (OCT2) gene is responsible for facilitating the transport of cationic compounds, which include both endogenous substrates and clinical drugs. Single nucleotide polymorphisms (SNPs) within this gene were extensively explored in the South African black population as little research has been conducted on these individuals so far. We sequenced the OCT2 promoter region of 10 DNA samples from the South African black population and identified four SNPs and one INDEL. We performed a luciferase assay to determine their effects on gene expression and we found two variants (rs59695691 and rs138765638) that showed a statistically significant change in luciferase expression suggesting that they may be associated with a change in OCT2 regulatory function. We also indentified thirteen SNPs and two INDELs within the OCT2 promoter region, and nine SNPs within the OCT2 coding region through analysing various South African population studies. These variations could affect both gene expression and protein function. These findings help contribute to filling the gap pertaining to OCT variation in South African populations. / LG2017

Leptin, a 16 (kilo Dalton) kDa hormone secreted predominantly by white adipocytes, regulates reproduction, energy intake and expenditure, and is involved in immune system function. Previous studies have identified associations between polymorphism E2FB in the leptin gene (lep) of cattle and milk quality and quantity, feed intake, and fat deposition in dairy and beef cattle though further studies have shown inconclusive results. Furthermore, indigenous South African cattle have not been involved in lep investigations or the applicability of the marker in South African beef grading systems. An investigation was conducted into the association of an SNP of a cytosine (C) to thymine (T) SNP (single nucleotide polymorphism) mutation in exon 2 of the bovine lep (leptin) gene with weight gain, body condition, carcass fat content and quality in a population of indigenous Nguni cattle (n = 70) as well as a population of exotic British Hereford cattle (n = 54). The Hereford population had higher T-allele frequencies and a lower P-value (P = 0.172) for the E2FB genotypes than the Nguni population (P = 0.958). The resulting E2FB lep genotypes CC, CT and TT did not show an association with the pre- and post-slaughter traits initial live weight (ILW), body condition score (BCS), slaughter live weight (SLW), carcass fat content (FAT), carcass conformation (CFN) or warm carcass mass (WCM) for either population though t-tests revealed an association with the CT genotype with increased ILW than TT and a significantly higher WG in the TT genotypes than the CT (P<0.05). Subsequently, differences in pre- and post-slaughter traits in both populations were largely attributable to breed differences. The Hereford population exhibited significantly higher WG, CFN, SLW, WCM and CCM (P<0.05) than the Nguni population. The Nguni displayed significantly higher ILW and BCS values when graded in terms of the commercial South African AAA feedlot system. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.