Estratégias de seleção, amostragem e mapeamento genético na seleção genômica

• Ano de defesa: 2009
• Autor(a) principal: Jangarelli, Marcelo
• Orientador(a): Euclydes, Ricardo Frederico
• Banca de defesa: Cruz, Cosme Damião , Souza, Gustavo Henrique de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Genética e Melhoramento
• Departamento: Genética animal; Genética molecular e de microrganismos; Genética quantitativa; Genética vegetal; Me
• País: BR
• Palavras-chave em Português: Distribuição dos extremos; Genotipagem seletiva; Marcadores moleculares; Simulação; QTL
• Palavras-chave em Inglês: Extremes distribution; Selective genotyping; Molecular markers; Simulation; QTL
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::GENETICA E MELHORAMENTO DOS ANIMAIS DOMESTICOS
• Link de acesso: http://locus.ufv.br/handle/123456789/1300

The simulation has contributed to the advancement of genomics in different areas of genetic improvement. The possibility of simulation of different scenarios, according to genetic assumptions and statistics of interest, optimizes the use of resources for analysis of genetic mapping and QTL studies. Different strategies of selection, sampling and mapping were simulated in this study, in order to estimate and compare the phenotypic performance in marker-assisted selection (MAS). Through the genetic simulation program Genesys three genomes were simulated, each one consisting of a single quantitative characteristic, whose only distinction was the value of the heritabilityof the character: 0,10; 0,40 and 0,70. A base population composed by 500 males and 500 females (1.000 individuals),unrelated to each other, was built from each simulated genomic structure. The initial populations were formed by the 1.000 descendents randomly selected in each base population, obtained from the crossing of 100 males and 100 females (1 female/male), producing 10 children/female/male (1.000 individuals). Each initial population was submitted to MAS by 20 consecutive generations. The selection was conducted with the purpose of increasing the phenotypic value. In Chapter 1, mating strategies between the parents selected were evaluated, in different sizes of family, through selective mating among the best and the worst, breeding only among the best and / or between the worst and random mating. In all scenarios of heritability and selection, selective breeding following the principle of selective genotyping, whose methodology uses individuals positioned at opposite extremes of the normal distribution of an evaluated parameter, was superior to the others. It was more effective in the phenotypic increment and minimization of endogamy averages and, consequently, in the detection of QTL over generations. By using the strategy of selective mating, smaller family size is required to optimize the phenotypic gain as the value of the heritability of the trait increases. In Chapter 2, this selective breeding was used to assess its ability to reduce the number of individuals required to optimize the phenotypic performance resulting from MAS. Each initial population, composed by 1.000 individuals, was subjected to 10 marker-assisted selections, in which the difference was in family size assumed over the selection process. Cluster analysis was realized with the phenotypic values resulting from selective processes, whose purpose was to obtain structures of classification among the family sizes to maximize the phenotypic growth. The selective breeding strategy was efficient in order to minimize the number of individuals needed in a mapping population for a particular phenotypic progress. As the magnitude of heritability rises, smaller family sizes are required to maintain the similarities in the phenotypic gains with the largest families. The use of samples with family sizes up to 30, 25 and 20 descendents, for the heritability 0,10; 0,40 and 0,70, respectively, is not necessary, according to the equivalent inferences indicated by the optimization method proposed by Tocher, originated from the Statistical Analysis System - SAEG. In the third chapter, the selective mating strategy was kept, assessing the genetic mapping in different levels of saturation by molecular markers. The difference from the previous chapters was in the initial populations, composed by 500 individuals randomly selected in each base population, obtained by crossing 50 males and 50 females (1 female/male), producing 10 children/female/male (500 individuals ). Each initial population was subjected to 15 marker-assisted selections, differing each other in the number of markers used in the genetic mapping. One more time, cluster analysis with phenotypic values resulting from the processes of selection was applied, in order to obtain structures of classification among the saturation levels, to benefit the phenotypic growth. The refinement using medium to high saturation by markers pointed efficiency in the phenotypic progress achieved with MAS. Lesser amounts of markers are required to maintain certain phenotypic progress as it increases the magnitude of heritability. Cluster analysis indicated optimization and correspondence in phenotypic answers when assuming the densities: i) 4 and 6 cM, ii) 4, 6, 8 and 10 cM, and iii) 6 and 8 cM, for heritabilities 0,10; 0,40 and 0,70, respectively.