Unraveling the genetic basis of hybrid vigor

Division of Biological Sciences, University of Missouri, Columbia, 65211, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 09/2006; 103(35):12957-8. DOI: 10.1073/pnas.0605627103
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Available from: James A Birchler
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    • "their homozygous parental inbred lines (Birchler et al., 2006; ). This aim may be achieved by heterosis breeding by using desired lines/varieties. "

    Full-text · Article · Jan 2016 · International Journal of Current Research
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    • "A third genetic model, referred to as " pseudo-overdominance, " is actually a simple case of dominance complementation in which the two genes are linked and the increasing alleles are inherited in repulsion, i.e. each parent contributes one of the two increasing alleles at two different but genetically linked genes to the hybrid. This type of complementation in the hybrid resembles overdominance , because of the tight chromosomal linkage and the co-inheritance of these genes as a single one [1]. In fact, distinction between the overdominance and dominance models should give an indication of how much the specific heterozygosity, as opposed to overall heterozygosity (proportional to the genetic distance between parents of the hybrids), causes heterosis. "
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    ABSTRACT: The genomic makeup and phenotypes of plants are diversifying, in part due to artificial or natural selection in agricultural and natural environments. Utilization of these variations to enhance crop productivity requires an understanding of the relationships between genotype and phenotype in inbreds and hybrids derived from crosses between these populations. This review highlights recent studies on hybrid vigor (heterosis) and the related phenomenon of hybrid weakness - two types of non-additive inheritance. Heterosis is a phenomenon whereby the phenotype of first-generation hybrids is superior to that of their parents. Intralocus interactions between alleles, complementation of dominant alleles, or inter-loci epistatic interactions are genetic mechanisms that may cause non-additive phenotypic inheritance in hybrids. However, there are different views on what portion of the heterotic variation is modulated by each of these mechanisms. Another aspect of plant vigor is phenotypic stability or robustness in different environments and how this is influenced by gene heterozygosity. Hybrids are not necessarily more phenotypically stable than inbreds since local heterozygosity might be associated with negative effects on biochemical activities. This review integrates genetic and biochemical considerations to illustrate how these relationships may be tightly linked with breeding system and sequence divergence.
    Full-text · Article · Dec 2014 · Plant Science
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    • "If overdominant loci are common, they should cause substantial reductions in fitness when organisms are inbred, and indeed, inbreeding depression is very common (Charlesworth & Charlesworth , 1987). However, data returning from long-term genetic studies of corn began to suggest that heterosis is caused more by pseudo-overdominance than genuine heterozygote advantage (Gardner, 1963; Moll et al., 1964; Crow, 1987; but also see Birchler et al., 2006). Here, pseudo-overdominance refers to elevated fitness in hybrids owing to complementation of recessive deleterious alleles at two closely linked genes (see Table 1 for definitions of some relevant terms). "
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    ABSTRACT: I. II. III. IV. V. VI. VII. VIII. References SUMMARY: Balancing selection refers to a variety of selective regimes that maintain advantageous genetic diversity within populations. We review the history of the ideas regarding the types of selection that maintain such polymorphism in flowering plants, notably heterozygote advantage, negative frequency-dependent selection, and spatial heterogeneity. One shared feature of these mechanisms is that whether an allele is beneficial or detrimental is conditional on its frequency in the population. We highlight examples of balancing selection on a variety of discrete traits. These include the well-referenced case of self-incompatibility and recent evidence from species with nuclear-cytoplasmic gynodioecy, both of which exhibit trans-specific polymorphism, a hallmark of balancing selection. We also discuss and give examples of how spatial heterogeneity in particular, which is often thought unlikely to allow protected polymorphism, can maintain genetic variation in plants (which are rooted in place) as a result of microhabitat selection. Lastly, we discuss limitations of the protected polymorphism concept for quantitative traits, where selection can inflate the genetic variance without maintaining specific alleles indefinitely. We conclude that while discrete-morph variation provides the most unambiguous cases of protected polymorphism, they represent only a fraction of the balancing selection at work in plants.
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