Avaliação de delineamentos genéticos em programas de melhoramento populacional recorrente, por meio de simulação / Evaluation of genetic delineation in programs of recurrent population improvement, through simulation

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Comstock and Robinson (1948) have suggested the evaluation of full-sib lineages obtained by crossing m male with f female distinct groups, in order to esteem the additive components, considering the dominance of the genotypic variance, and also the average degree of dominance. This system of controlled crossings was called Delineation I. The objective of this work was to analyze the genetic gains due to the selection and alterations in the population genotypic variance. Selection was performed between families of full sib, between families of full sib obtained using Delineation I, selection in tandem and selection between families of half sib. The merit of Delineation I was analyzed through simulations, as a crossings system in programs of recurrent population improvement, on the basis of realized gains. Thus, it was considered genic systems with 10 genes, associated to three values of heritability (10, 50 and 90%), in three population classes (little improved, much improved and with intermediate frequencies of the favorable genes). In each population class, seven characters were considered, representing distinct degrees of dominance (2 and -2, 1 and -1, 0,5 and -0,5 and 0). With degree of positive dominance, the favorable gene (the one that increases the expression of the character) is dominant and with negative degree of dominance it is recessive. The average gains were evaluated after 10 cycles of selection, each process of simulation being repeated 10 times. It was possible to validate the simulation process, since the obtained results were very similar to those presented in literature relating to experimental works on corn. It was verified that the strategy of selection between half sib families was the worst strategy when comparing the realized gains, in 73% of the evaluated situations. The selection strategy between full sib families was the best strategy in only 21% of the evaluated situations. The selection strategies using Delineation I presented the biggest carried through gains - as suggested by Comstock and Robinson - in the great majority of the observed cases (68,2%), throughout 10 cycles of selection. This demonstrates its potential use in programs of recurrent population improvement. Independent of the character, when the favorable gene is recessive or in situation of dominance absence, populations whose unit of selection was half sib families had retained bigger genotypic variability in the population in the tenth cycle. In many situations when the favorable gene was dominant and where the strategies of selection between full sib families were obtained using Delineation I and selection in tandem, it was observed that genotypic variability was high after 10 cycles of election. The loss of genes for drift was not very sharp, occurring basically in populations little improved or very improved, with recessive favorable gene. These were infrequent in the initial population and diminished with decreasing value of the average degree of dominance. On the basis of the obtained results, it was concluded that the best unit of selection is full sib family and the best strategy of selection is between full sib families using Delineation I, as suggested by Comstock and Robinson.

ASSUNTO(S)

half sib families plant genetics full sib family delineamento i famílias de irmãos completos delineation i seleção de plantas famílias de meios-irmãos plant selection melhoramento genético genética vegetal genetica quantitativa breeding

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