So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

Continued growth and intensi¢cation of aquaculture production depends upon the development of sustainable protein sources to replace ¢sh meal in aquafeeds. This document reviews various plant feedstuis, which currently are or potentially may be incorporated into aquafeeds to support the sustainable production of various ¢sh species in aquaculture. The plant feedstuis considered include oilseeds, legumes and cereal grains, which traditionally have been used as protein or energy concentrates as well as novel products developed through various processing technologies. The nutritional composition of these various feedstuis are considered along with the presence of any bioactive compounds that may positively or negatively aiect the target organism. Lipid composition of these feedstuis is not speci¢cally considered although it is recognized that incorporating lipid supplements in aquafeeds to achieve proper fatty acid pro¢les to meet the metabolic requirements of ¢sh and maximize human health bene¢ts are important aspects. Speci¢c strategies and techniques to optimize the nutritional composition of plant feedstuis and limit potentially adverse eiects of bioactive compounds are also described. Such information will provide a foundation for developing strategic research plans for increasing the use of plant feedstuis in aquaculture to reduce dependence of animal feedstuis and thereby enhance the sustainability of aquaculture.

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Expanding the utilization of sustainable plant products in aquafeeds: a review

Medical genetics was revolutionized during the 1980s by the application of genetic mapping to locate the genes responsible for simple Mendelian diseases. Most diseases and traits, however, do not follow simple inheritance patterns. Geneticists have thus begun taking up the even greater challenge of the genetic dissection of complex traits. Four major approaches have been developed: linkage analysis, allele-sharing methods, association studies, and polygenic analysis of experimental crosses. This article synthesizes the current state of the genetic dissection of complex traits—describing the methods, limitations, and recent applications to biological problems.

Genetic Dissection of Complex Traits

Heritability allows a comparison of the relative importance of genes and environment to the variation of traits within and across populations. The concept of heritability and its definition as an estimable, dimensionless population parameter was introduced by Sewall Wright and Ronald Fisher nearly a century ago. Despite continuous misunderstandings and controversies over its use and application, heritability remains key to the response to selection in evolutionary biology and agriculture, and to the prediction of disease risk in medicine. Recent reports of substantial heritability for gene expression and new estimation methods using marker data highlight the relevance of heritability in the genomics era.

Heritability in the genomics era — concepts and misconceptions

Flowering time is a complex trait that controls adaptation of plants to their local environment in the outcrossing species Zea mays (maize). We dissected variation for flowering time with a set of 5000 recombinant inbred lines (maize Nested Association Mapping population, NAM). Nearly a million plants were assayed in eight environments but showed no evidence for any single large-effect quantitative trait loci (QTLs). Instead, we identified evidence for numerous small-effect QTLs shared among families; however, allelic effects differ across founder lines. We identified no individual QTLs at which allelic effects are determined by geographic origin or large effects for epistasis or environmental interactions. Thus, a simple additive model accurately predicts flowering time for maize, in contrast to the genetic architecture observed in the selfing plant species rice and Arabidopsis.

/pdf/the-genetic-architecture-of-maize-flowering-time-247vcudvzn.pdf

The Genetic Architecture of Maize Flowering Time

The Illinois Long Term Selection Strains offer a unique opportunity to investigate the quantitative genetic basis of kernel chemical traits. This study was conducted to determine the number and magnitude of quantitative trait loci (QTL) influencing kernel oil concentration and kernel weight in a maize (Zea mays L.) population derived from a cross of Illinois High Protein (IHP) × Illinois Low Protein (ILP). The parental strains had been divergently selected for protein concentration for 76 cyles, yet varied in oil concentration from 29 g kg -1 (ILP) to 54g kg -1 (IHP) and in 300 kernel weight from 76.5g (ILP) to 41.1g (IHP) [...]

Molecular Markers Associated with Maize Kernel Oil Concentration in an Illinois High Protein × Illinois Low Protein Cross

The use of molecular markers to enhance plant breeding efforts is being widely studied. A major area of research is the use of molecular markers to identify and manipulate chromosome segments QTL (quantitative trait locus or loci depending on context) controlling quantitative traits. The objective of this paper is to review the theory and results associated with the use of molecular markers to manipulate QTL in plant breeding programs. First, methods of identifying marker-QTL associations are considered (.)

Molecular Markers in Plant Improvement: Manipulation of Genes Affecting Quantitative Traits

In one of the longest-running experiments in biology, researchers at the University of Illinois have selected for altered composition of the maize kernel since 1896. Here we use an association study to infer the genetic basis of dramatic changes that occurred in response to selection for changes in oil concentration. The study population was produced by a cross between the high- and low-selection lines at generation 70, followed by 10 generations of random mating and the derivation of 500 lines by selfing. These lines were genotyped for 488 genetic markers and the oil concentration was evaluated in replicated field trials. Three methods of analysis were tested in simulations for ability to detect quantitative trait loci (QTL). The most effective method was model selection in multiple regression. This method detected ∼50 QTL accounting for ∼50% of the genetic variance, suggesting that >50 QTL are involved. The QTL effect estimates are small and largely additive. About 20% of the QTL have negative effects (i.e., not predicted by the parental difference), which is consistent with hitchhiking and small population size during selection. The large number of QTL detected accounts for the smooth and sustained response to selection throughout the twentieth century.

https://www.genetics.org/content/genetics/168/4/2141.full.pdf

The genetic architecture of response to long-term artificial selection for oil concentration in the maize kernel.

Maize selection passes the century mark: a unique resource for 21st century genomics

In maize (Zea mays L.) breeding programs identifying potentially high yielding hybrids, assigning new inbreds to heterotic groups, and determining the parental line in a hybrid to which a potential donor line is most closely related, are significant problems. Data from a diallel cross among 14 maize inbreds were analyzed to evaluate use of molecular marker date to (i) predict yield potential of hybrids, (ii) assign inbreds to heterotic groups, and (iii) determine to which of the two inbred parents of a single cross a donor line is most closely related (...)

John W. Dudley

Papers

Molecular Markers Associated with Maize Kernel Oil Concentration in an Illinois High Protein × Illinois Low Protein Cross

Molecular Markers in Plant Improvement: Manipulation of Genes Affecting Quantitative Traits

The genetic architecture of response to long-term artificial selection for oil concentration in the maize kernel.

Maize selection passes the century mark: a unique resource for 21st century genomics

Molecular Markers and Grouping of Parents in Maize Breeding Programs