Generation mean analysis in relation to polygenic systems with epistasis and fixed genes

Abstract

-Epistatic effects involving genic combinations of fixed and non fixed genes are shown to contribute to the genotypic mean of any population. These effects define specific additive x additive and additive x dominant epistatic components. As such components are not estimable, their relative importance cannot be assessed. These epistatic effects can cause bias in the estimates of the additive and dominance components to which they are confounded. The magnitude of the bias depends on the relative values of the epistatic effects, comparatively to deviations d and h, type of prevailing epistasis and direction of dominance.Index terms: biometrical genetics, components of means. ANÁLISE DE MÉDIAS DE GERAÇÕES EM RELAÇÃO A SISTEMAS POLIGÊNICOS COM EPISTASIA E GENES FIXADOSRESUMO -Neste artigo é demonstrado que efeitos epistáticos envolvendo combinações de genes fixados e não fixados contribuem para a média genotípica de qualquer geração. Estes efeitos definem componentes epistáticos específicos, dos tipos aditivo x aditivo e aditivo x dominante. Como tais componentes não são estimáveis, suas importâncias relativas não podem ser avaliadas. Estes efeitos epistáticos podem ser causa de viés nas estimativas dos componentes aditivo e de dominância, com os quais estão confundidos. A magnitude do viés depende dos valores relativos dos efeitos de interação entre genes não alélicos, comparativamente aos desvios d e h, do tipo predominante de epistasia e da direção dos efeitos de dominância.Termos para indexação: genética biométrica, componentes de médias.

Effects of Deforestation on the Onset of the Rainy Season and the Duration of Dry Spells in Southern Amazonia

“…Other studies have investigated the occurrence of dry spell events in several regions of Brazil and the largescale climatic variations associated with them (Assad et al, 1993;Carvalho et al, 2000;Minuzzi et al, 2005;Silva & Rao, 2002;Sleiman, 2008). However, Erfanian et al (2017) argued that recent dry periods in the Amazon cannot be explained only by changes in sea surface temperature, suggesting that other factors are contributing to severe drought.…”

Research Article Genetic control of internode length in winter squash (<i>Cucurbita</i> <i>moschata</i>)

“…The absence of significant dominance effects for ILAF in the dominant × additive model can be explained by the manifestation of epistatic effects in the control of the evaluated characteristics. According to Viana (2000), epistatic interactions tend to increase the biases in estimates of additive and dominant genetic components, and thus should be studied using the complete model rather than partial models.…”

“…Specifically, there was likely duplicated epistasis in the significant additive × additive and dominant × dominant effects found for both ILAF and ILBF. According to Viana (2000), duplicated epistasis can cause problems in estimating additive and dominance effects because it introduces bias into such estimates. In addition, the dominant × dominant epistasis had a high-magnitude and negative parameter value in the complete model, thus contributing to decreases in internode length.…”

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“…The generation mean analysis (GMA) is a simple but effective approach for the estimation of the nature and magnitude of gene actions (additive or dominance) involved in a particular trait. Besides this, GMA also helps breeders in the detection of various types of epistasis, viz., additive × additive, additive × dominance and dominance × dominance operating in the inheritance of a particular trait [35][36][37][38][39].…”