Cytochrome P4502E1 (CYP2E1), the ethanol-inducible isoform of cytochrome P450 superfamily, catalyzes many low molecular weight endogenous and exogenous compounds, including ethanol, acetone, drugs like acetaminophen and chlorzoxazone, and industrial solvents like benzene and styrene, most of which are carcinogenic. Besides, it has a high capacity to produce reactive oxygen species. CYP2E1 is induced by ethanol and isoniazid, as well by some pathophysiological conditions like diabetes and starvation. CYP2E1 gene shows genetic polymorphisms which are thought to play a major role in interindividual variability in drug response and in susceptibility to chemical-induced diseases, like several types of cancers. It is well established that CYP2E1 polymorphisms vary markedly in frequency among different ethnic and racial groups. Therefore, in this study, the frequency of two important CYP2E1 polymorphisms / the single nucleotide polymorphisms C-1019T / G-1259C in 5&rsquo / -flanking region and T7678A poymorphism in intron 6, in Turkish population was investigated. For this purpose, whole blood samples were collected from 132 healthy volunteers representing Turkish population and genomic DNA for each subject was isolated in intact form. The genotypes were determined by PCR amplification of corresponding regions followed by restriction endonuclease RsaI, PstI (for C-1019T / G-1259C SNPs) and DraI (for T7678A SNP) digestions. The genotype frequencies, for C-1019T / G-1259C SNPs, which are in complete linkage disequilibrium, were investigated on 116 DNA samples, and determined as 97.4% for homozygous wild type (c1/c1), 2.6% for heterozygotes (c1/c2) and 0.0% for homozygous mutants (c2c2). The allele frequency of wild type allele (c1) was calculated as 98.7% and that of mutated allele (c2) as 1.3%. The genotype frequencies for T7678A SNP, investigated in 108 DNA samples were determined as 80.6% for homozygous wild type (DD), 19.4% for heterozygotes (CD) and 0.0% for homozygous mutants (CC). The corresponding allele frequencies were 90.3% for wild type allele (D), and 9.7% for mutated allele (C). Genotype frequencies of both polymorphisms fit Hardy-Weinberg equation and showed no significant difference with respect to gender. The genotype distributions of both polymorphisms showed similarity when compared to other Caucasian populations like French, Swedish, German, and Italian populations, while both polymorphisms studied differed significantly from Chilean, Japanese, Taiwanese and Chinese populations, as compared with Chi-Square test.

Thesis (Ph.D. (Plant Production)) -- University of Limpopo, 2021 / Cassava (Manihot esculenta Crantz) is a widely cultivated crop in many tropical countries in Africa, Latin America, and Asia. Cassava is a staple food security crop for over one billion people worldwide. It is a multi‑purpose and well adapted to different agricultural production systems. Although cassava is adaptable to marginal soils with low fertility, and to irregular rainfall conditions, as it allows a relatively stable productivity and flexibility for harvesting process, the challenges posed by global climate change (both temperature and drought severity increasing) have caused negative impacts on this crop‘s productivity. Given the increasing demand for higher productivity to improve food security and alleviate poverty in the dry prone regions of Africa, there is a concurrent increasing demand to expand production into marginal ecologies and improve its adaptation in such ecologies. Breeding efforts have resulted in the development of high-yielding varieties, but due to late bulking and long time taken before crop is ready for harvest, the improved varieties were not easily adopted by farmers. The complex nature of yield and other productivity traits, coupled with the biology of cassava, make it more challenging to improve the crop. However, biotechnology has revolutionised breeding with the development of advanced molecular tools that have facilitated breeding-by-design approaches leading to effective manipulation of genes for complex traits. The potential and impact of the new tools are now providing a stronger basis to adopt molecular breeding to genetically improve the crop for key traits. The main objectives of the research were to: (i) Develop a mapping population and identify traits driving the physiological basis of drought tolerance in F1 cassava genotypes; (ii) Identify traits linked with early bulking in the F1 population; (iii) Identify quantitative trait loci (QTLs) for drought tolerance and early bulking in F1 cassava genotypes; and (iv) Estimate the genetic improvement for drought tolerance in the F1 population. Two genotypes (TMS98/0505 and TMS98/0581) with contrasting desirable traits such as high yield in marginal environment, good disease resistance, vigour, and flowering potentials were used in the development of the mapping population used in this study. Results indicate that there was a positive correlation between yield, yield-related traits .and morphological/physiological traits. Principal component analysis identified the scar level, height of stem with leaf, fresh root yield, dry root yield, root number and dry-matter content as traits driving drought tolerance in marginal environment. This study also identified early-bulking cassava varieties in the F1 population and traits associated with early bulking. Fresh root yield was significantly associated with morphological and productivity traits while principal component analysis identified important traits such as root weight, root number, plant biomass, fresh root yield, plant height, , and stem diameter. Composite interval mapping identified 27QTLs and 30 QTLs in the first and second year, respectively, associated with the traits phenotyped in dry savannah ecology of Nigeria, while 16 and 12 QTLs associated with early bulking at 7 MAP were identified in the first and second year. Identification of these loci will aid breeding for drought tolerance and early root bulking in cassava. There was a better performance among traits such as biomass, root number, dry-matter content, number of scars, number of leaves, and length of stem with leaf in the second population (population C) than in the first population (population B). Twenty superior genotypes were selected from population C, which will be incorporated in the breeding programmes for further evaluation and germplasm enhancement. KEY WORDS: Composite interval mapping, Fresh root yield, Manihot esculenta, morphological traits, Population C, physiological traits. / National Root Crops Research Institute (NRCRI) Umudike