• Congwei Sun

      Articles written in Journal of Genetics

    • QTL mapping for combining ability in different population-based NCII designs: a simulation study

      Lanzhi Li Congwei Sun Yuan Chen Zhijun Dai Zhen Qu Xingfei Zheng Sibin Yu Tongmin Mou Chenwu Xu Xhongli Hu

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      The NCII design (North Carolina mating design II) has been widely applied in studies of combining ability and heterosis. The objective of our research was to estimate how different base populations, sample sizes, testcross numbers and heritability influence QTL analyses of combining ability and heterosis. A series of Monte Carlo simulation experiments with QTL mapping were then conducted for the base population performance, testcross population phenotypic values and the general combining ability (GCA), specific combining ability (SCA) and Hmp (midparental heterosis) datasets. The results indicated that:

      increasing the number of testers did not necessarily enhance the QTL detection power for GCA, but it was significantly related to the QTL effect.

      The QTLs identified in the base population may be different from those from GCA dataset. Similar phenomena can be seen from QTL detected in SCA and Hmp datasets.

      The QTL detection power for GCA ranked in the order of DH(RIL) based > F2 based > BC based NCII design, when the heritability was low.

      The recombinant inbred lines (RILs) (or DHs) allows more recombination and offers higher mapping resolution than other populations. Further, their testcross progeny can be repeatedly generated and phenotyped. Thus, RIL based (or DH based) NCII design was highly recommend for combining ability QTL analysis. Our results expect to facilitate selecting elite parental lines with high combining ability and for geneticists to research the genetic basis of combining ability.

    • Genomewide mapping reveals a combination of different genetic effects causing the genetic basis of heterosis in two elite rice hybrids

      Lanzhi Li Xiaohong He Hongyan Zhang Zhiming Wang Congwei Sun Tongmin Mou Xinqi Li Yuanming Zhang Zhongli Hu

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      North Carolina design III (NCIII) is one of the most powerful and widely used mating designs for understanding the genetic basis of heterosis. However, the quantitative trait mapping (QTL) conducted in previous studies with this design was mainly based on analysis of variance (ANOVA), composite interval or multiple interval mapping methods. These methodologies could not investigate all kinds of genetic effects, especially epistatic effects, simultaneously on the whole genome. In this study, with a statistical method for mapping epistatic QTL associated with heterosis using the recombinant inbred line (RIL)-based NCIII design, we conducted QTL mapping for nine agronomic traits of two elite hybrids to characterize the mode of gene action contributing to heterosis on a whole genomewide scale. In total, 23 main-effect QTL (M-QTL) and 23 digenic interactions in IJ (indica × japonica) hybrids, 11 M-QTL and 82 digenic interactions in II (indica × indica) hybrid QTLs were identified in the present study. The variation explained by individual M-QTL or interactions ranged from 2.3 to 11.0%. The number of digenic interactions and the total variation explained by interactions of each trait were larger than those of M-QTL. The augmented genetic effect ratio of most M-QTL and digenic interactions in (L1–L2) data of two backcross populations (L1 and L2) showed complete dominance or overdominance, and in (L1 + L2) data showed an additive effect. Our results indicated that the dominance, overdominance and epistatic effect were important in conditioning the genetic basis of heterosis of the two elite hybrids. The relative contributions of the genetic components varied with traits and the genetic basis of the two hybrids was different.

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