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

An Introduction to Genetic Statistics.

The need for increased sustainability of performance in cereal varieties, particularly in organic agriculture (OA), is limited by the lack of varieties adapted to organic conditions. Here, the needs for breeding are reviewed in the context of three major marketing types, global, regional, local, in European OA. Currently, the effort is determined, partly, by the outcomes from trials that compare varieties under OA and CA (conventional agriculture) conditions. The differences are sufficiently large and important to warrant an increase in appropriate breeding. The wide range of environments within OA and between years, underlines the need to try to select for specific adaptation in target environments. The difficulty of doing so can be helped by decentralised breeding with farmer participation and the use of crops buffered by variety mixtures or populations. Varieties for OA need efficient nutrient uptake and use and weed competition. These and other characters need to be considered in relation to the OA cropping system over the whole rotation. Positive interactions are needed, such as early crop vigour for nutrient uptake, weed competition and disease resistance. Incorporation of all characteristics into the crop can be helped by diversification within the crop, allowing complementation and compensation among plants. Although the problems of breeding cereals for organic farming systems are large, there is encouraging progress. This lies in applications of ecology to organic crop production, innovations in plant sciences, and the realisation that such progress is central to both OA and CA, because of climate change and the increasing costs of fossil fuels.

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Developments in breeding cereals for organic agriculture

Chilling and heat requirements of almond cultivars for flowering

Several claims have been made about genetic engineering (GE) in comparison with crop domestication and classical plant breeding, including the similarity of genetic changes between those taking place during domestication and by GE, the increased speed and accuracy of GE over classical plant breeding, and the higher level of knowledge about the actual genes being transferred by GE compared with classical breeding. In reviewing evidence pertaining to these claims, I suggest that (i) it is unlikely that changes introduced by GE will make crops weedier, although exceptions have been noted, (ii) changes brought about by GE currently often involve gain-of-function mutations, whereas changes selected during domestication generally involve loss-of-function mutations, (iii) adoption of GE cultivars has been much faster than any previous introduction and spread of agriculture that occurred earlier but has occurred at about the same rate as the spread of cultivars obtained by plant breeding, (iv) introduction of agriculture reduced the health of agriculturists compared with that of hunter-gatherers, suggesting that introduction of innovations do not automatically improve well being, (v) although GE is not a substitute for plant breeding, it can significantly contribute to plant breeding by generating additional genetic diversity, (vi) uncertainties associated with the site of insertion of transgenes in the genome and the expression of transgenes following insertion, makes GE less rapid and precise than originally claimed, and (vii) a potential advantage of GE over classical breeding is the knowledge of the actual gene(s) being inserted, although few cases of unwanted gene introductions through classical plant breeding have been documented. Further advances in GE will increase the precision of the technique, its relevance to consumers, and its environmental friendliness. What is most needed are evenhanded, case-by-case assessments of the benefits and potential pitfalls of GE in comparison with other crop improvement techniques. Classical plant breeding may, in the end, also be regulated in the same way as GE.

A comparison between crop domestication, classical plant breeding, and genetic engineering

Preface. 1. Genetic Foundations: The Historical Setting. Part One: Quantitative Variation: Its Detection, Estimation and Utilization. 2. Genetic Models and their Predictive Value. 3. Experimental Mating Designs: An Assessment of their Use and Efficiency in Breeding Programs. 4. The Diallel Cross: The Ultimate Mating Design? 5. Selection with and without Competition. Part Two: Genotype and Environment: Their Interrelationships. 6. Genotype-Environment Interactions: Analysis and Problems. 7. Stability, Adaptability and Adaptation. 8. Breeding for Biotic and Abiotic Stress. 9. Genetic Resources, Genetic Diversity and Ecogeographic Breeding. Index.

Quantitative and Ecological Aspects of Plant Breeding

As we have already seen, most of those characters with which a plant breeder works vary continuously, and are controlled by several genes whose individual effects are too small to be detected by conventional Mendelian methods. Instead, the properties of these genes have to be inferred from analyses of the means and variances of appropriate generations or populations. We have already established, however, that the genes concerned obey the Mendelian laws of genetics, a premise which forms the basis of the models presented here.

Genetic models and their predictive value

Allied to the phenomena of genotype—environment interactions, discussed in the previous chapter, are the topics of stability, adaptability and adaptation, topics which arouse considerable interest among plant breeders. Indeed, not only do they excite interest, they often cause confusion because terms such as phenotypic stability, yield stability, adaptability and adaptation are frequently used interchangeably, to the extent that (1957) was moved to say that ‘the word adaptation has a great adaptability’. Before entering into the details of the statistical procedures required to estimate them, we will describe some of the basic concepts which have been proposed to understand the reaction of genotypes or populations to changing environments.

Stability, adaptability and adaptation

The genetic potential of breeding material commonly needs to be assessed in multi-environment trials. These environments may be artificial, such as different levels or combinations of fertilizer, or natural, such as different seasons or locations, or a combination of both. However environments are created, the analysis of such trials may well disclose the presence of genotype—environment interactions. As Comstock and Moll (1963) wrote

Genotype—environment interactions: analysis and problems

There are between 400 000 and 700 000 vascular plant species in the world, including angiosperms, gymnosperms and pteridophytes. Of these: 


about 200 000 are flowering plants


3000 may be potentially useful for human purposes


100 are important crops today


8 are major food crops (wheat, maize, rice, potato, barley, sweet potato, cassava and soya bean), of which


3 — wheat, maize and rice — constitute some 50% of the per capita food supplies for direct human consumption (FAO, 1995).

P. M. A. Tigerstedt

Papers

Quantitative and Ecological Aspects of Plant Breeding

Genetic models and their predictive value

Stability, adaptability and adaptation

Genotype—environment interactions: analysis and problems

Genetic resources, genetic diversity and ecogeographic breeding