Plectritis congesta and P. brachystemon are two very closely related species which grow sympatrlcally, and differ in their: breeding system, some associated morphological (floral) characters, and isozyme phenotypes. Plectritis congesta is approximately 70% outcrossed in nature, while P. brachystemon is less than 3% outcrossed in natural populations. Theory would predict that, all other things being equal, the outcrossed species would be more variable genetically than the selfed species. Since selection acts on genetic variability, the two species could be expected to respond differently to it. Six generations of plants of both species were grown under controlled conditions, and measured for a number of characters. Control and treatment (selection for tall and short height, and for early and late anthesis) populations were maintained. Two sets of P. congesta populations were maintained, one outcrossed (approximately 65%) and one selfed (outcrossed approximately 15%); the P. brachystemon populations were naturally self-pollinating. Selection pressure in the experiment was approximately 90%; 20 of the 200 plants in any population were selected to form the next -generation, on the basis of height or flowering time in the treatment populations, and at random in the control populations. The P. congesta populations responded to divergent selection for height at anthesis, indicating that genetic variability for this character was present in the populations. The outcrossed lines, PCO, diverged 66% or 148 mm from the control line; the selfed lines, PCS, diverged 78% or 175 mm. There were no significant differences between the outcrossed and selfed P. congesta lines over the course of the experiment. Two estimates of narrow sense heritability - realised heritability (b[sub=c]) and parent-offspring: regression (h²) - quantified this genetic variability: in PCO b[sub=c] = 0.53, h² = 0.45: in PCS b[sub=c] = 0.58, h² = 0.44. There was a decline in the phenotypic variance for height at anthesis in the P. corigesta lines selected for this character. In contrast, the P. brachystemon populations did not respond to selection for height at anthesis, and appear to have no detectable genetic variability for this character. Both species appear to have significant genetic variability for flowering time, as both responded to divergent selection for this character. The PCO lines diverged 33.5% or 31.8 days from the control line, the PCS lines diverged 28.7% or 27.3 days, and the P. brachystemon lines, PBS,-diverged 18.5% or 21.5 days. According to the heritability estimates, P. congesta is more variable genetically: in the PCO lines b[sub=c]=0.77, h² = 0.60; in PCS b[sub=c]= 0.75, h² = 0.72; while in PBS b[sub=c]= 0.49, and h²= 0.42. There was a decline in the phenotypic variance for flowering time in all three species groups. Of the other measured but unselected characters - number of days to emergence, number of nodes at anthesis, number of primary branches at anthesis, and fruit production - some responded to the selection pressure with divergence, notably those characters which were correlated with the selected characters (for example, number of nodes at anthesis, correlated with flowering time). With others there was no change which could be attributed to the selection procedure. There was no evidence from two qualitative characters - fruit wing phenotype and fruit pubescence pattern phenotype - for any response to selection; dispersion in both characters was not significantly different from that expected to result from random drift. The relatively high increase in aberrant characters in the P. congesta lines compared to the P. brachystemon lines is probably indicative of inbreeding depression in the normally outcrossed P. congesta. It appears that despite the difference in breeding system, the two Plectritis species are able to maintain variability by similar processes (genetic) in some characters, as in flowering time, and by different processes (genetic in P. congesta, phenotypic in P. brachystemon) in other characters, as in height at anthesis. Thus one quantitative character, height at anthesis, follows the pattern predicted by the breeding system difference, with the outcrossed P. congesta being much more variable genetically than the selfed P. brachystemon. This agrees with the levels of variability observed by Layton (1980) in electrophoretically detectable isozymes, and observed by Ganders and Maze (unpublished) in metrical fruit characters. The other quantitative character, flowering time, shows considerable genetic variance in the populations of the selfed P. brachystemon, though less than in the populations of P. congesta. The maintenance of such relatively high levels of genetic variability in the face of the strong inbreeding pressures which must be present in P. brachystemon populations is certainly adaptive, and probably comes about through occasional outcrossing and multiniche selection for variability among the segregating lines. / Science, Faculty of / Botany, Department of / Graduate

Counterfeit Integrated Circuits (ICs) are previously used ICs that are resold as new. They have become a serious problem in modern electronic devices. They cause lower performance, reduced life span and even catastrophic failure of systems and platforms. To prevent counterfeiting and the associated revenue loss, there is need for non-invasive and inexpensive techniques to establish the authenticity of devices. We describe a technique to detect a counterfeit IC that does not have any special anti-counterfeiting mechanisms built-in prior to deployment. Our detection criterion is based on measuring path delays. The experiments show that a single path delay cannot directly reveal the age, as it is also greatly influenced by process variation and this could result in large error in classifying ICs as authentic or counterfeit. �Instead, we establish that the relationship between the delays of two or more paths is a great indicator for the age of device. The idea is to project ICs from different age groups onto the space of the path delays and train a trusted reference hyper-surface for each age group. Ideally, the hyper-surfaces do not overlap. In this way, an IC under test can be assigned to one hyper-surface based on the distance of its footprint with respect to these hyper-surfaces, thus predicting its age. In our simulations, we observe over 97% correct prediction of identifying an aged IC from a new IC. / Master of Science

Environmental variation of Thamnocortus insignis Mast. (Restionaceae) is presented, by using average dry weight measurements of six populations of this species found along the coast of the Cape Province. The dry weight measurements were used to detect variation in the growth rates of the six populations, which in tum indicates the environmental variation among the populations. The results were showed no significant difference between all six populations and this was due to the relatively very small sizes of the seedlings when the measurements were taken. Genetic variation was investigated by using isozyme electrophoresis of the EST locus. One population (Puntjie) showed significant deviation from the Hardy-Weinberg equilibrium, whilst all the others agreed with the assumptions of the model except for the Superthatch-extra tall population, which was homologous. Estimation of allelic diversity among the populations produced a Fst of 0.098 that implies that there is a high level of gene flow among the six populations of the species. The allelic diversity estimate within populations was also very low (Fis = 0.079) implying that the genetic neighbourhoods are relatively large and there is a high incidence of gene flow within the populations. Both estimation results support the predicted results for dioecious wind-pollinated species such as T. insignis.

Student Number : 0318625T - MSc dissertation - School of Molecular and Cell Biology - Faculty of Science / Genetic variation in haptoglobin, a plasma protein, has been reported to be associated with susceptibility to and the rate of HIV/AIDS progression. The purpose of this study was to investigate the influence of haptoglobin polymorphism on HIV/AIDS in black South Africans. Polymorphism in the coding region of the haptoglobin gene was detected by direct DNA and allele-specific amplification. Polymorphism in the coding region of the gene was detected by amplification of DNA and by polyacrylamide gel electrophoresis of plasma protein. A statistically significant association was observed between allele -61C and resistance to HIV infection. The Hp0 phenotype, in which no haptoglobin protein is detected, was associated with HIV status and some promoter genotypes. Since in our study population there were a few samples with usable clinical data , further investigations need to be done to confirm the association of the -61C allele and the Hp0 phenotype with the risk of HIV infection.

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The investigation of the waters of Lake Bridgeport is to obtain data essential for a satisfactory understanding of the physical and chemical factors on the aquatic life. These factors detremine the kinds of food available for life there.

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