Elizângela Emídio Cunha

Characterization of genotypes and estimates of genetic parameters of productive traits for forage sorghum

Avaliou-se o desempenho produtivo de 29 genotipos de sorgo forrageiro por meio dos dados de materia verde, materia seca, altura da planta, floracao inicial e sobrevivencia da planta. Alem do desempenho, foram estimadas a herdabilidade de cada caracteristica e as correlacoes genotipicas e fenotipicas entre elas, as quais sao uteis nos programas de melhoramento genetico empregando-se selecoes direta e indireta. Utilizou-se o delineamento em blocos completos ao acaso com tres repeticoes, em analise de variância univariada. Houve variabilidade genetica para todas as caracteristicas, com diferencas significativas entre as medias dos genotipos. A herdabilidade foi elevada, sobretudo para altura da planta. As correlacoes genotipica e fenotipica da materia verde com a materia seca (0,83 e 0,76, respectivamente) e da materia seca com a altura da planta (0,87 e 0,72) foram expressivas. As correlacoes foram medianas entre materia verde e altura da planta (0,61 e 0,52) e entre materia verde com a sobrevivencia (0,71 e 0,61). A floracao inicial foi a caracteristica menos correlacionada as demais. A altura da planta, por ser medida antes do corte e ter apresentado herdabilidade muito alta, alem de correlacao genotipica moderada com a materia verde e alta com a materia seca, ambas medidas apos o corte, pode ser utilizada para obtencao de ganho genetico nessas caracteristicas via selecao indireta.Productive performance of 29 genotypes of forage sorghum was evaluated by data of fresh matter, dry matter, plant height, initial flowering and plant survival. Heritability was also estimated for each trait, as well as the genotypic and phenotypic correlations among them. Such parameters are useful in genetic breeding programs by using direct and indirect selection. Randomized complete block design with three replications was used, in univariate analysis of variance. Genetic variability for all traits was observed and the genotype means were significantly different. Heritability presented high values, mainly for plant height. Genotypic and phenotypic correlations between fresh matter and dry matter (0.83 and 0.76, respectively) and dry matter with plant height (0.87 and 0.72) produced high values. Correlations were moderate among fresh matter and plant height (0.61 and 0.52) and among fresh matter with survival (0.71 and 0.61). Initial flowering was the trait less strongly correlated with the others. Because plant height was recorded before cutting and for showing high heritability and moderate genotypic correlation with fresh matter and a high one with dry matter, both of them observed after cutting, it appears to be feasible as to achieve genetic breeding for those traits through indirect selection.

Oscilação genética em populações submetidas a métodos de seleção tradicionais e associados a marcadores moleculares

The effect of genetic drift in populations under selection with different effective sizes was evaluated using data simulated by the GENESYS program. Selection was applied during 20 generations based on Individual selection (IS) using breeding values predicted by classical best linear unbiased prediction (BLUP) and BLUP associated with molecular markers (BLUPM). The similarity matrix used in BLUPM was obtained by simulation of 100 micro-satellites markers (simple sequence repeats) using a similarity coefficient corresponding to the mean Euclidean distance for quantitative data. Six populations of selection were simulated corresponding to two effective sizes (18.18 and 66.66), and three mating systems of selected sires (random mating, exclusion of half sibs and exclusion of half as well as full sibs). The average phenotypic value was the parameter of evaluation. Large variation on average phenotypic values was due to genetic drift, mainly for BLUP and BLUPM methods and also for populations with small effective sizes. The results indicate genetic drift may cause large variation in genetic gains by selection in breeding programs designed for small populations.

Efeito de tipos de acasalamentos e razões sexuais na seleção baseada no BLUP

ABSTRACT - Different mating types were evaluated, through simulated data, in populations submitted to selection based on BLUP,during fifty generations. It was considered one quantitative trait with heritability of 0,10. The selected populations had the followingdata structure: mating ratio values: 10, 20, 25, and 50, numbers of selected males by generation: 10, 5, 4, and 2, and effective populationsizes: 36,36, 19,05, 15,38 and 7,84, respectively. In each mating ratio value, the populations were coupled according one of the matingtypes: preferential mating to half and full sibs, preferential mating between half sibs, random mating, exclusion of mating between fullsibs and exclusion of mating to half and full sibs. The genetic parameters evaluated were average phenotypic values and average inbreedingby generation. In the lowest mating ratio value, it was observed better phenotypic performance in all the mating types. The mating typeswhich didn’t allow mating between sibs provided higher phenotypic gains and were more effective in controlling the inbreeding, in theshort-term selection, although they didn’t avoid neither the increasing, nor the inbreeding accumulation, along the generations.Key Words: inbreeding, simulated data, long-term selection, effective population sizes

Endogamia, fixação de alelos e limite de seleção em populações selecionadas por métodos tradicionais e associados a marcadores moleculares

This study aimed to evaluate the inbreeding coefficient, alleles fixation and selection limit in a population selected during 20 generations. Selection was based on breeding values predicted by classical best linear unbiased prediction (BLUP), BLUP associated with molecular markers (BLUPM) and individual selection (IS) using different mating designs. The genetic similarity matrix used in BLUPM was obtained by simulating 100 micro satellite markers (simple sequence repeats) using a similarity coefficient corresponding to the mean Euclidean distance between quantitative data. The selection methods were compared using populations with an effective size of 66.66 and a mean of 30 repetitions. The largest increase in inbreeding was observed for BLUPM, followed by BLUP and SI. The methods based on BLUP provided the higher fixation of favorable and unfavorable alleles. The BLUPM method provided the higher reduction in the selection limit during the twenty generations. Systems excluding between sibs mating resulted in lower increases in inbreeding rates, fewer losses due to unfavorable allele fixation and smaller decreases in selection limit.

Erros na classificação de touros, vacas e touros jovens geneticamente superiores avaliados na presença de heterogeneidade

Foram simuladas quatro estruturas de dados com diferentes padroes de heterogeneidade entre rebanhos e com diferentes graus de conexidade genetica. As estruturas simuladas diferiam quanto aos parâmetros heterogeneos entre rebanhos: 1) heterogeneidade para todos os parâmetros; 2) medias geneticas homogeneas e demais parâmetros heterogeneos; 3) heterogeneidade para parâmetros fenotipicos; e 4) rebanhos sem heterogeneidade. Apos a predicao dos valores geneticos, calculou-se a porcentagem de animais comuns entre dois grupos de classificacao para os animais geneticamente superiores: grupo 1 - classificacao com base nos valores geneticos verdadeiros e grupo 2 - classificacao com base nos valores geneticos preditos. Para dados com heterogeneidade para todos os parâmetros e 0% de conexidade genetica, a porcentagem de touros comuns aos dois grupos de classificacao foi baixa e houve grandes erros na classificacao dos touros geneticamente superiores. Quando os rebanhos possuiam 100% de conexidade genetica, esta porcentagem foi superior a 73% e os erros na classificacao dos touros foram menores. Para vacas e touros jovens, mesmo para dados com 100% de conexidade genetica entre rebanhos, a predicao dos valores geneticos foi muito afetada pela presenca da heterogeneidade para todos os parâmetros. Para as estruturas sem heterogeneidade para media genetica, as porcentagens de animais comuns entre os grupos de classificacao foram altas e os erros na classificacao dos animais geneticamente superiores foram pequenos, mesmo havendo heterogeneidade para outros parâmetros. Esses resultados sugerem que a heterogeneidade entre rebanhos para medias geneticas teve grande efeito sobre a acuracia da predicao dos valores geneticos dos animais. Contudo, quando a heterogeneidade entre os rebanhos ocorreu para outros parâmetros como variância genetica, media fenotipica e variância fenotipica, os resultados das avaliacoes geneticas dos animais foram proximos aos obtidos para dados sem heterogeneidade entre rebanhos.

Variabilidade genética e limite da seleção em populações de diferentes tipos de acasalamento

Populations of five different mating designs, submitted to selection based on best linear unbiased predicto (BLUP)r, were evaluated regarding to genetic losses by fixation of unfavorable alleles and selection limit, during 50 generations. Simulated data were used to obtain the genome of all individuals of the populations. A quantitative trait with heritability of 0.10 was studied in the selected populations, with the following structure: sexual ratio of 10, 20, 25, and 50 and effective population size of 36.36, 19.05, 15.38 and 7.84, respectively. For each sexual ratio different populations were generated corresponding to the following mating designs: preferential matings between half and full sibs, preferential matings between half sibs, random matings, exclusion of matings between full sibs and exclusion of matings of half and full sibs. Smallest percentage of unfavorably fixed loci and the highest selection limit were observed in the lower sexual ratio (d= 10). Better differentiation between the studied mating designs was also observed for the lower sexual ratio.

Impacts of ignoring the non-additive genetic effects of dominance on animal genetic evaluation

The objective of this study was to evaluate impacts of ignoring the dominance effects on the estimation of genetic parameters and prediction of genetic values by the restricted maximum likelihood method, under the additive animal model, using MTDFREML. Two gene action models were simulated for the same genomic architecture: one model that included only additive effects of the genes and the other with additive effects and positive and complete dominance into 100% of the loci. Under each genetic model, three base populations were generated corresponding to the characteristics with heritabilities of 0.15 (low), 0.30 (average) and 0.60 (high). Starting from the base populations the initial populations were generated which by selection and mating at random, for six consecutive and discrete generations, each one produced 18,000 animals with record. The estimates of the components of variance and heritability obtained in the model with additive gene action were similar to the actual values for all traits, while under dominance gene action, every component was overestimated, especially the additive genetic variance. The non-estimated dominance variance by the animal model adopted was redistributed between the additive genetic and residual components estimated. Accuracy was lost in the genetic evaluation, under the genetic model with dominance, that resulted in smaller correlations between the actual and predicted breeding values of the animals. Additional studies are needed since the simulated genome might not correspond to the true biological systems.

Seleção tradicional e associada a marcadores moleculares na avaliação genética animal

Resumo – O objetivo deste trabalho foi comparar a selecao, utilizando valores geneticos preditos pelo BLUP classico (BLUP), BLUP marcadores (BLUPM) e pela selecao individual (SI), usando simulacao com o programa Genesys. Para obter a matriz de similaridade genetica utilizada no BLUPM, foram simulados cem marcadores moleculares do tipo microssatelite (SSR – Simple Sequence Repeat), por meio de um coeficiente de similaridade correspondente a distância euclideana media para dados quantitativos. A fim de comparar os diferentes metodos, utilizaram-se populacoes com tamanho efetivo de 66,66 e media de 30 repeticoes, avaliando-se os valores fenotipicos medios. Os ganhos ao longo das 20 geracoes de selecao foram maiores para o BLUP em relacao ao BLUPM, e este foi superior a SI. Quanto ao ganho obtido nas cinco primeiras geracoes, o BLUPM apresentou ganhos semelhantes ao BLUP e superiores a SI. Diferentes sistemas de acasalamento dos reprodutores selecionados nao revelaram diferencas em ganho genetico nos metodos baseados no BLUP. Termos para indexacao: BLUP, selecao fenotipica, simulacao, sistemas de acasalamento. Traditional and associated selection with molecular markers in the genetic evaluation of animals

Ratios between variability components of simulated quantitative traits with genetic effects of dominance and overdominance

Ratios were assessed between variability components of quantitative traits simulated from the genome incorporating non-additive genetic effects in random mating populations and short-term phenotypic selection. A trait of low (h2 = 0.10) heritability and another of high (h2 = 0.60) heritability were studied, both influenced by 600 bi-allelic loci. Five gene action models were simulated, of which four included complete and positive dominance for 25, 50, 75 and 100% of the loci (D25, D50, D75 and D100, respectively); and one model included positive overdominance for 50% of the loci. Every model included additive effects of the alleles for 100% of the loci. The main quantified ratios were d2 (dominance variance/phenotypic variance) and d2a (dominance variance/additive variance). For both traits, d2 and d2a increased according to the increase in the variance of dominance with the growing inclusion of loci with dominance deviation and under overdominance. For the same model, both ratios, especially d2, are greater under high heritability, that indicates that the dominance effects explain the greater part of the total variability of this trait under selection.

Comparação de metodologias de seleção sob oscilação genética

Determinou-se o numero adequado de repeticoes na comparacao de metodos de selecao tradicionais e associados a marcadores moleculares, com diferentes tamanhos efetivos e sob diferentes sistemas de acasalamento dos reprodutores selecionados, usando simulacao com o programa GENESYS. Para comparar os diferentes metodos de selecao utilizaram-se populacoes com tamanhos efetivos de 18,18 (TE1) e de 66,66 (TE2) e uma, 10 e 30 repeticoes por geracao, avaliando-se os valores fenotipicos medios. Para as situacoes com apenas uma repeticao, os resultados apresentaram incoerencias, independentemente do tamanho efetivo (TE1 ou TE2) ou do sistema de acasalamento (RAA - reprodutores acasalados aleatoriamente, EIC - exclusao de irmaos completos ou EICMI - exclusao de irmaos completos e meio-irmaos). Observou-se que a oscilacao genetica influencia o ganho genetico, principalmente, em populacoes com pequeno tamanho efetivo e que um valor minimo de 10 repeticoes por geracao e necessario para assegurar a consistencia dos resultados obtidos pelos metodos de selecao.