The mechanisms that control growth processes in biology tissues have attracted continuous research interest despite their complexity. With the emergence of big data experimental approaches there is an urgent need to develop statistical and computational models to fit the experimental data and that can be used to make predictions to guide future research. In this work we apply statistical methods on growth process of different biological tissues, focusing on development of neuron dendrites and tumor cells. We first examine the neuron cell growth process, which has implications in neural tissue regenerations, by using a computational model with uniform branching probability and a maximum overall length constraint. One crucial outcome is that we can relate the parameter fits from our model to real data from our experimental collaborators, in order to examine the usefulness of our model under different biological conditions. Our methods can now directly compare branching probabilities of different experimental conditions and provide confidence intervals for these population-level measures. In addition, we have obtained analytical results that show that the underlying probability distribution for this process follows a geometrical progression increase at nearby distances and an approximately geometrical series decrease for far away regions, which can be used to estimate the spatial location of the maximum of the probability distribution. This result is important, since we would expect maximum number of dendrites in this region; this estimate is related to the probability of success for finding a neural target at that distance during a blind search. We then examined tumor growth processes which have similar evolutional evolution in the sense that they have an initial rapid growth that eventually becomes limited by the resource constraint. For the tumor cells evolution, we found an exponential growth model best describes the experimental data, based on the accuracy and robustness of models. Furthermore, we incorporated this growth rate model into logistic regression models that predict the growth rate of each patient with biomarkers; this formulation can be very useful for clinical trials. Overall, this study aimed to assess the molecular and clinic pathological determinants of breast cancer (BC) growth rate in vivo.

THE ABSTRACT In the new global economy majority of the developed countries use imposition of sanctions in the case of some offences. I have applied the synthetic control methods on this particular case of political pressure to quantify the real costs of anti-Russian sanctions to the economy. Based on the results of this study it was identified, that real GDP growth rate of Russia was continuously reducing by about -1,19% per quarter on average. Reaching the highest value of sanction's effect of -2,8% in real GDP growth rate at the end of 2015. It was also revealed that sanctions had positive effect on current account balance of Russia, that indicator was increasing during the whole studied after sanction's period by about 3,15% per quarter on average. This thesis is presented as a research of interconnection the imposition of 2014 sanctions against Russia and indicators of economic development (GDP, inflation) using synthetic control methods. It was revealed that former economic and social mechanisms aren't capable to provide further development of economy of Russia, its self-sufficiency and safety. JEL Classification F12, F21, F23, H25, H71, H87 Keywords sanctions, synthetic control method, Russia, GDP growth rate, current account balance Author's e-mail 51375259@fsv.cuni.cz Supervisor's e-mail...

Microclimatic gradients may have large influence on individual vital rates and population growth rates of species, and limit their distributions. Therefore, I focused on the influence of microclimate on individual performance and distribution of species. Further, I examined differences in how microclimate affect species with contrasting distributions or different ecophysiological traits, and populations within species. More specifically, I investigated the performance of northern and southern distributed forest bryophytes that were transplanted across microclimatic gradients, and the timing of vegetative and reproductive development among northern, marginal and more southern populations of a forest herb in a common garden. Also, I compared the landscape and continental distributions across forest bryophytes and vascular plants and, thus, their distribution limiting factors at different spatial scales. Lastly, I examined the population dynamics across microclimatic gradients of transplants from northern and southern populations of a forest moss. The effects of microclimatic conditions on performance differed among bryophytes with contrasting distributions. There were no clear differences between northern and southern populations in the timing of development of a forest herb or in the population dynamics of a moss. However, within each region there was a differentiation of the forest herb populations, related to variation in local climatic conditions and in the south also to proportion of deciduous trees. The continental distributions of species were reflected in their landscape distributions and vice versa, in terms of their occurrence optima for climatic variables. The variation in landscape climatic optima was, however, larger than predicted, which limit the precision for predictions of microrefugia. Probably, the distributions of vascular plants were more affected by temperature than the distributions of bryophytes. Bryophytes are sensitive to moisture conditions, which was demonstrated by a correlation between evaporation and the population growth rate of a forest moss. We might be able to predict species’ landscape scale distributions by linking microclimatic conditions to their population growth rates, via their vital rates, and infer larger scale distribution patterns. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p> / EkoKlim

Em ambientes degradados, a restauração ecológica visa acelerar o processo de sucessão ecológica. A técnica mais utilizada para a restauração de ambientes muito degradados é o plantio de mudas. A seleção das espécies é determinante para o sucesso dos projetos de restauração, pois as espécies precisam se estabelecer e crescer diante das condições do ambiente. Utilizar a abordagem de características funcionais pode ser uma ferramenta promissora para auxiliar a seleção de espécies em projetos de restauração. Em ambientes florestais, há evidências de que as características funcionais afetam o desempenho das espécies, entretanto, existem poucos estudos realizados em áreas em restauração. Neste estudo, foi avaliada a relação entre as características funcionais foliares e a taxa de crescimento relativo em altura e em diâmetro à altura do solo de espécies arbóreas nativas plantadas em uma área degradada que está sendo restaurada. Para descrever a relação entre as características funcionais e a taxa de crescimento relativo (TCR) dos indivíduos foi utilizada a abordagem de seleção de modelos baseados em modelos lineares de efeitos mistos (MLEM). A seleção de modelos foi realizada utilizando o critério de informação de Akaike (Akaike\'s Information Criterion) (AIC). As características funcionais não apresentaram relação com a taxa de crescimento relativo em altura e diâmetro dos indivíduos das espécies, possivelmente devido às diferenças nas condições ambientais entre ambientes florestais e ambientes degradados. Apesar de não ter sido encontrada uma relação entre as características funcionais e a TCR, o modelo mais plausível selecionado indica que indivíduos maiores no início do monitoramento possuem menores taxas de crescimento relativo em altura, ou seja, indivíduos mais altos possuem menores taxas de crescimento em altura. Isso pode ser um indicativo de que as espécies analisadas possuem taxa de crescimento relativo dependente do tamanho. Considerando que não foi encontrada relação entre as características funcionais morfológicas e a taxa de crescimento relativo em uma área em restauração, é razoável supor que essa abordagem não pode ser utilizada em todos os ambientes. Estudos que avaliem características funcionais foliares nos diferentes estágios de desenvolvimento das plantas em ambientes degradados podem refinar essas análises e ajudar a definir se a seleção de espécies para projetos de restauração pode ser feita usando a abordagem de características funcionais / In degraded environments, ecological restoration aims to accelerate the process of ecological succession. The most widely used technique for restoration of degraded environments is the planting of seedlings. The selection of species is crucial to the success of the restoration projects, because the species need to establish and grow under the harsh conditions of the environment. Using the approach of functional traits can be a promising tool to assist in the selection of species in restoration projects. In forest environments, there is evidence that functional traits affect the performance of the species, however, there are few studies conducted in areas undergoing restoration. In this study, the relationship between the functional leaf traits and the relative growth rate in height and in diameter at ground level of native tree species planted in a degraded area that is being restored was evaluated. To describe the relationship between the functional traits and the relative growth rate (RGR) of individuals, we used the approach of model selection based on linear mixed effects models (LMEM). The selection of models was performed using Akaike\'s Information Criterion (AIC). The functional traits showed no relationship with the relative growth rate in height and diameter of the individuals of the species, possibly due to differences in environmental conditions between forest environments and degraded environments. Despite not finding a relationship between the functional traits and the RGR, the most plausible model selected indicates that larger individuals at the beginning of monitoring have lower relative growth rates in height, that is, taller individuals have lower rates of growth in height. Considering that no relationship between the morphological functional traits and the relative growth rate in an area undergoing restoration was found, it is reasonable to assume that this approach cannot be applied in all environments. Studies that assess functional traits of the leaf in the different stages of plant development in degraded environments can refine these analyses and help define whether the selection of species for restoration projects can be accomplished using the approach of functional characteristics

Este trabalho iniciou-se com o objetivo de superexpressar proteínas com atividade ATPase, como tentativa de alterar a conservação de energia livre na levedura S. cerevisiae, de maneira a aumentar o rendimento da fermentação alcoólica. Para isso, duas ATPases nativas de S. cerevisiae, as chaperonas codificadas pelos genes HSP104 e CDC48, foram superexpressas, individualmente, sob o controle de quatro promotores de diferentes forças, provocando diferentes gastos energéticos na levedura. Entretanto, não foi possível obter aumento no rendimento em etanol. Em seguida, foi feito um estudo que visou comparar essas linhagens em situação de estresse térmico, ácido ou osmótico, tipicamente encontrados no processo brasileiro de produção de etanol. A 40 °C, uma linhagem superexpressando CDC48 apresentou velocidade específica máxima de crescimento 17 % maior que a linhagem de referência, indicando maior tolerância ao estresse térmico. Finalmente, avaliou-se Hsp104 e Cdc48 em um contexto fisiológico no qual as atividades dessas proteínas pudessem ser mais requeridas. Como as chaperonas moleculares são conhecidas por agirem como primeira linha de defesa contra a formação de proteínas incorretamente enoveladas e agregados proteicos, estudaram-se a morfologia e a fisiologia da superexpressão de HSP104 e CDC48 em linhagens com desarranjo no controle de qualidade de proteínas intracelulares, causado por mutações no proteassomo 20S. A superexpressão de CDC48 ou HSP104 reverteu em parte a morfologia alterada de alguns desses mutantes de proteassomo. / The initial goal of this work was to overexpress proteins with ATPase activity in Saccharomyces cerevisiae, as an attempt to alter the conservation of free energy in this yeast, in order to increase alcoholic fermentation yield. Therefore, two native S. cerevisiae ATPases, the chaperones encoded by HSP104 and CDC48, were individually overexpressed under the control of four promoters with different strengths, in order to provoke different levels of energy expenditure. Increments in the ethanol yield could not be observed in any of the constructed strains. Subsequently, a study was carried out to compare these mutant strains with reference strains under heat, acid or osmotic stress, which are typically found in the industrial fuel ethanol production in Brazil. At 40 oC a strain overexpressing CDC48 displayed a maximum specific growth rate 17 % higher than that of the reference strain, indicating a greater tolerance to heat stress. Finally, Hsp104 and Cdc48 were evaluated in a physiological context in which the activity of these proteins would be required in a higher level. Since molecular chaperones are known to act as the first defense line against the formation of misfolded proteins and aggregates, the physiological and morphological effects of HSP104 or CDC48 overexpression were analyzed in strains with protein quality control disarrangements caused by mutations in proteasome 20S. The overexpression of either CDC48 or HSP104 partially reversed the altered morphology of some of these proteasome mutants.

Cette thèse est dédiée au développement d’un modèle mathématique multi-échelle pour la régulation du cycle cellulaire par l’horloge circadienne. Ceci est motivé par le fait que plusieurs études ont montré un lien direct entre certains cancers et un dysfonctionnement du mécanisme de l’horloge circadienne. Le but est de comprendre l’effet des rythmes circadiens et leur perturbation sur la prolifération d’une population de cellules / This thesis is dedicated to the development of a multiscale mathematical model that describes the regulation of the cell cycle by the circadian clock. What motivated this work is the fact that several tumorigenic diseases are linked to circadian rhythms disruption. We would like to understand the effect of circadian rhythms on the proliferation of a cell population and hence give plausible explanation for diseases that arise form circadian clock disruption. The mammalian cell cycle and the circadian clock are two molecular processes that operate in a rhythmic manner and exquisite precision. On one hand, the cell cycle is driven by the rhythmic activity of cyclin dependent kinases which dictate the time a cell must engage mitosis and the time it must divide giving birth to two daughter cells. On the other hand, the circadian clock is a system of transcriptional and translational feedback-loops that generates sustained oscillations of different mRNAs and proteins with a period of approximately 24 h. It turns out that several components of the circadian clock regulates various cyclin-dependent kinases at different stages of the cell cycle. This makes the circadian clock a key player of the temporal organization of the cell cycle and makes these two biological processes act as two tightly coupled oscillators. Our modeling approach consists of using a molecular-structured partial differential equation that describes the proliferation of a cell population. Proliferation depends on the coupled cell cycle-circadian clock molecular state of cells. Due to the large number of molecular components involved in the cell cycle-circadian clock system, the problem becomes of high-dimensionality and specific numerical techniques are needed to solve the equation

Made available in DSpace on 2016-04-27T18:12:21Z (GMT). No. of bitstreams: 1 Byanka.pdf: 779527 bytes, checksum: 7203ac54ab45b641ad5cdb18a4434b5c (MD5) Previous issue date: 2007-05-16 / Fundação de Amparo a Pesquisa do Estado de São Paulo / Introduction: The study of Distortion Product Otoacoustic Emission Input/Output Function (DPOAE I/O) is a very useful instrument to access and to understand the cochlear physiology, specially the mechanism of compression, the cochlear non-linearity and the function of outer hair cells. Therefore, the importance of studies about the possible clinic applications of this test arises. The mechanisms of cochlear physiology still represent an important object of study; consequently, the researches that try to identify the possible clinic applications with the varied kinds of Otoacoustic Emissions (OAE) will result in a relevant development of the audiology area. Objective: To describe the results of the Distortion Product Otoacoustic Emission Input/Output Function (DPOAE I/O) of individuals with regular audiometric thresholds. Method: The DPOAE I/O were researched in the frequencies of 1kHz, 1,5kHz, 2kHz, 3kHz, 4kHz, 5kHz and 6kHz in 104 ears; it should be considered that 44 of these ears were male and 60 of them were female. The level of L2 varied from 45 to 75dBSPL, L1= 0,4*L2 + 39dB, and f1/f2 = 1,22. The equipment used was the ILO 292 USB II with software ILO V6 Otodynamics. Results: The results demonstrated meaningful statistic differences between the DPOAE I/O of the gender in the frequencies of 5kHz and 6kHz, and between the right and the left ears in the frequencies of 3kHz, 4kHz and 6kHz. It is important to note that meaningful statistic differences were also observed between the averages of slopes related to the gender in the frequencies of 5kHz and 6kHz. However, differences related to the age group of the population were not observed. Conclusions: The outcomes of DPOAE I/O and the values of female slopes were higher than the male slopes in the frequencies of 5kHz and 6kHz in both ears. While in the DPOAE I/O of 3kHz, 4kHz and 6kHz there was a tendency of higher outcomes from the right ear than from the left ear. The higher occurrence of absent outcomes in the DPOAE I/O was in the frequency of 6kHz and at the level of L2=45dB. Differences related to the age group of the population were not observed / Introdução: O Estudo da Função de Crescimento das EOAPD têm se mostrado um instrumento muito favorável para o acesso e entendimento da fisiologia coclear, em especial ao mecanismo de compressão e à não-linearidade coclear além do funcionamento das células ciliadas externas. Desta forma, emerge a importância de estudos acerca das possíveis aplicações clínicas deste teste. Os mecanismos da fisiologia coclear ainda representam um importante objeto de estudo e, desta forma, pesquisas que tentem identificar possíveis aplicações clínicas com os diversos tipos de EOA trarão importantes avanços no campo da Fonoaudiologia. Objetivo: Descrever os resultados da Função de Crescimento das Emissões Otoacústicas - Produto de Distorção em indivíduos com limiares audiométricos normais. Método: Foram pesquisadas as FC-EOAPD nas freqüências de 1kHz, 1,5kHz, 2kHz, 3kHz, 4kHz, 5kHz e 6kHz, em 104 orelhas sendo 44 orelhas do sexo masculino e 60 do sexo feminino. O nível de L2 variou de 45 a 75dBNPS e L1= 0,4*L2+39dB e f1/f2 = 1,22. Foi utilizado o equipamento ILO 292 USB II com software ILO V6 Otodynamics. Resultados: Os resultados encontrados demonstraram diferenças estatisticamente significativas entre as FC-EOAPD dos sexos nas freqüências de 5kHz e 6kHz e entre orelhas nas freqüências de 3kHz, 4kHz e 6kHz. Também foram observadas diferenças estatisticamente significativas entre a médias do slopes em relação ao sexo nas freqüências de 5kHz e 6kHz. Não foram encontradas diferenças no que se refere à idade da população. Conclusões: As respostas da FC-EOAPD e os valores dos slopes do sexo feminino se apresentaram maiores que no sexo masculino nas freqüências de 5kHz e 6kHz em ambas orelhas. Nas FC-EOAPD de 3kHz, 4kHz e 6kHz houve uma tendência das respostas da orelha direita se apresentarem maiores que na orelha esquerda. A maior ocorrência de respostas ausentes nas FC-EOAPD foi na freqüência de 6kHz e no nível de L2 = 45dB. Não foram observadas diferenças em relação à faixa etária da população

A citricultura brasileira apresenta números bastante significativos e expressivos, refletindo a grande importância social e econômica que essa atividade agrícola e industrial tem para a economia do país. O Brasil se destaca como o maior produtor de laranja do mundo. As plantas cítricas podem ser produzidas e multiplicadas de várias formas e a enxertia é a forma de propagação vegetativa mais utilizada comercialmente no Brasil. Dentre os porta-enxertos mais empregados, sobressaem-se o citrumeleiro Swingle e a tangerineira Sunki. Apesar das vantagens presentes nesses dois genótipos, a produção deles está sendo limitada por doenças causadas por fungos e estraminipilas. Em citros, as diversas espécies de Phytophthora são responsáveis pelas doenças gomose e podridões, principalmente de radicelas. P. nicotianae é a espécie que mais afeta as plantas cítricas no Brasil. Não obstante a grande importância de P. nicotianae para os porta-enxertos, alguns mecanismos de resistência ou susceptibilidade ainda requerem mais investigações cientificas. O presente trabalho visa a elucidação de alguns mecanismos de resistência dos citros a P. nicotianae, por meio de estudos fisiológicos e bioquímicos dos porta-enxertos, além da ação de meios de cultura e da qualidade da luz no estudo da fisiologia desse estraminipila. Para isso realizou-se a detecção de alguns equivalentes de compostos fenólicos através da técnica HPLC e o comportamento do genótipo resistente frente à possível inibição da síntese de compostos fenólicos através do tratamento das raízes do porta-enxerto Swingle com Pro-Ca; avaliou-se a atração de zoósporos de P. nicotianae por exsudatos radiculares provenientes dos dois porta-enxertos com o uso de uma armadilha adaptada; verificou-se o comportamento do zoósporo, a motilidade e a zoosporogênese frente à ação de vários compostos fenólicos e testou-se a ação de diferentes meios de culturas e da qualidade da luz no crescimento micelial e na esporulação de P. nicotianae. Os resultados revelaram que a tangerineira Sunki possui maiores quantidades de equivalentes em apigenina que o citrumeleiro Swingle nos dois períodos de avaliação, para o HPLC. O porta-enxerto resistente apresentou mais equivalentes de ácido clorogênico que o genótipo susceptível. Quanto ao Pro-Ca, os equivalentes de compostos fenólicos em raízes de plântulas do citrumeleiro Swingle não diferiram daquelas plantas tratadas com água. O Pro-Ca não inibiu e não desativou a síntese de compostos fenólicos. O uso do anticorpo contra a elicitina \"&alpha;-plurivorina\" teve resultados intermediários no consumo de água por plântulas de tangerineira Sunki e a atividade zoosporicida dos compostos fenólicos apresentou resultados variáveis no comportamento da motilidade de zoósporos. Os compostos fenólicos escopoletina e tricetinpentametoxi conseguiram paralisar a motilidade e proporcionaram as menores porcentagens de zoosporogênese. O meio de cultura AA permitiu a maior TCMD, seguido de CA e V8-CaCO3-Ágar. Os maiores valores de esporulação foram encontrados nesses dois últimos meios, respectivamente. Todas as faixas de luzes (e a ausência de luz) estudadas no presente trabalho podem ser avaliadas para o crescimento micelial, porém o tratamento claro foi aquele que mais induziu a esporulação de zoósporos de P. nicotianae. / The Brazilian citrus industry has very significant and expressive numbers, reflecting the great social and economic importance of this industrial and agricultural activity has for the economy. Brazil stands out as the world\'s largest orange producer. Citrus plants can be produced and multiplied in various ways and the bud is the form of vegetative propagation more commercially used in Brazil. Among the most commonly used rootstocks, stand up the Swingle citrumelo and Sunki mandarin. Despite the advantages these two genotypes present, their production is being limited by diseases caused by fungi and estraminipilas. In citrus, all species of Phytophthora are responsible for diseases gummosis and fibrous root rot, especially. P. nicotianae is the kind that affects citrus plants in Brazil. Regardless of the great importance of P. nicotianae for rootstocks, some mechanisms of resistance or susceptibility still require further scientific investigation. This study aims to elucidate some mechanisms of resistance of citrus to P. nicotianae, through physiological and biochemical studies of rootstocks, beyond of action culture media and quality of light in the physiological study of this estraminipila. To this was carried out to detect certain equivalent of phenolic compounds by HPLC and genotype resistant behavior against the possible inhibition of the synthesis of phenolic compounds by treatment of the roots of Swingle rootstock with Pro-Ca; evaluated the zoospores attraction P. nicotianae by exudates from the two rootstocks using an adapted trap; it was the zoospore behavior, motility and zoosporogenesis to the action of various phenolic compounds and tested the action of different culture media and quality of light on mycelial growth and sporulation of P. nicotianae. The results for HPLC revealed that Sunki mandarin has larger amounts of apigenin equivalents Swingle citrumelo in that the two periods. The sturdy rootstock had more chlorogenic acid equivalents of the susceptible genotype. As for the Pro-Ca equivalent of phenolic compounds in Swingle seedling roots not differ from those plants treated with water. The Pro-Ca not inhibited and not disabled the synthesis of phenolic compounds. The use of the antibody against elicitin \"&alpha;-plurivorin\" had intermediate results in water consumption by Sunki mandarin seedlings and zoosporicide activity of phenolic compounds showed variable results in the behavior of zoospore motility. The scopoletin and tricetinpentametoxi phenolic compounds managed to paralyze the motility and provided the smallest percentages of zoosporogenesis. The culture medium AA allowed greater DMGR, followed by CA and V8-CaCO3-Agar. The highest sporulation values were found in the last two media, respectively. All lights tracks (and the absence of light) studied in this work can be evaluated for mycelial growth, but the treatment light was that more induced sporulation of zoospores of P. nicotianae.

O fósforo (P) que é um nutriente pouco disponível em solos tropicais devido a sua deficiência natural e também por causa da imobilização do mesmo em constituintes do próprio solo, formando fosfatos insolúveis e assim indisponíveis as plantas. A solubilização destes fosfatos inorgânicos é uma estratégia para aumentar a disponibilidade deste nutriente no solo. Uma forma seria a utilização de microrganismos solubilizadores de P que deixam este nutriente disponível às plantas. Desta forma, o presente trabalho teve como objetivos: (i) avaliar o crescimento do cafeeiro em função das fontes e doses de P2O5; (ii) determinar o fósforo disponível e (iii) avaliar o estado nutricional do cafeeiro, em função da fonte e dose de P2O5. O desenvolvimento das mudas de cafeeiro é superior com o uso de fonte de P solúvel, em relação à fonte de solubilidade gradual, independentemente da dose. A determinação da capacidade de substituição da fonte solúvel pela fonte de solubilidade gradual depende do tempo de reação no solo, cuja máxima equivalência é igual a 84 %, aos 180 dias após a aplicação do fertilizante (MSF). Em solos com teor de P disponível suficiente para a cultura do cafeeiro é viável a substituição de uma fonte solúvel (SFS) por outra de baixa solubilidade associada à micro-organismos (MSF). / Phosphorus (P) which is a little available nutrient in tropical soils due to their disability and also because natural impoundment of the same constituents in the soil itself, forming insoluble phosphates and thus unavailable to plants. The solubilization of inorganic phosphate is a strategy to increase the availability of this nutrient in the soil. One way would be to use P-solubilizing microorganisms that make nutrients available to plants that. Thus, this study aimed to: (i) evaluate the growth of coffee as a function of the sources and levels of P2O5, (ii) determine the available phosphorus and (iii) assess the nutritional status of coffee, depending on the source and dose of P2O5. The development of coffee seedlings is higher with the use of soluble P source, in relation to the source of gradual solubility regardless of dose. The determination of the replacement capacity of the water soluble source of gradual solubility depends on the reaction time in the soil, whose maximum equivalence is equal to 84% at 180 days after fertilizer application (MSF). In soils with a sufficient level of available P for the cultivation of coffee is feasible to replace a water soluble (SFS) for another low solubility associated with micro-organisms (MSF).

Thesis (M. Sc. Agriculture (Animal Production)) -- University of Limpopo, 2018 / Two experiments were conducted to determine the effect of replacing maize meal with a low tannin sorghum meal (Macia) on productivity, gut morphology, carcass characteristics and bone morphometrics of Ross 308 broiler chickens aged one to 42 days. In each experiment, a total of 160 Ross 308 broiler chickens were assigned to a complete randomized design with 5 treatments, replicated 4 times with 8 chickens per replicate. Five diets were formulated to contain sorghum replacement levels at 0, 25, 50, 75 and 100% to meet the nutrient requirements of Ross 308 broiler chickens. Data was analysed using statistical analysis of variance. The first experiment determined the effect of replacing maize meal with a low tannin white sorghum meal on productivity and gut morphology of unsexed Ross 308 broiler chickens aged 1 to 21 days. Feed intake, growth rate, feed conversion ratio, live weight, N-retention, caecum and large intestine digesta pH, large intestine lengths, crop, gizzard, caecum and large intestine weights, gut intestinal villi height, crypt depth and villi height to crypt depth ratio of unsexed Ross 308 broiler chickens were not affected (P>0.05) by the treatment effects. However, replacement of maize meal with sorghum meal improved (P<0.05) metabolisable energy intake and small intestine digesta pH values. It was concluded that maize meal can be replaced by a low tannin white sorghum meal in the diet without adverse effects on unsexed Ross 308 broiler chickens aged one to 21 days. The second experiment determined the effect of replacing maize meal with sorghum meal on productivity, gut morphology, carcass characteristics and bone morphometrics of Ross 308 male broiler chickens aged 22 to 42 days. Replacing maize meal with sorghum meal had no effect (P>0.05) on feed intake, feed conversion ratio (FCR), live weight and nitrogen retention (N-retention) of male Ross 308 broiler chickens aged 22 to 42 days. Replacing maize meal with sorghum meal improved (P<0.05) ME intake and growth rate of the chickens. Caecum and large intestine digesta pH, GIT, caecum and large intestine lengths, small intestine, caecum and large intestine weights, gut intestinal villi height, crypt depth and villi height to crypt depth ratio, drumstick, thigh and wing weights, drumstick, thigh and wing colour, meat sensory evaluation, meat pH and bone morphometrics of male Ross 308 broiler chickens were not affected (P>0.05) by replacement of maize meal with sorghum vii meal. It was concluded that maize meal can be replaced by a low tannin white sorghum meal at 25, 50, 75 and 100% levels without causing adverse effects on productivity and carcass characteristics of male broiler chickens aged 22 to 42 days. Key words: Low tannin sorghum meal, Maize meal, Broiler chickens, Growth rate, Carcass characteristics. / National Research Foundation (NRF)