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Chapter

Cover Plants, Genes & Agriculture

The Domestication of Our Food Crops  

Paul Gepts

This chapter assesses crop domestication, discussing how and where modern crops arose from wild plants. Wheat was domesticated in the Middle East, and domestication resulted in diploid (Einkorn), tetraploid (durum or pasta wheat), and hexaploid (bread wheat) varieties. Meanwhile, three varieties of rice — japonica, indica, and aus — were domesticated in different parts of Asia. The chapter then looks at the domestication of maize and beans, before considering how domestication has accelerated evolution because of selection pressures imposed by humans and farming techniques. Crop evolution has been marked by major genetic bottlenecks that follow domestication, dispersal to new regions, and scientific breeding programs. The result is decreased genetic diversity in most crops. The chapter also studies hybridization, polyploidy, and the sequencing of crop-plant genomes.

Chapter

Cover Plants, Genes & Agriculture

Genes, Genomics, and Molecular Biology  

The Basis of Modern Crop Improvement

Kranthi K. Mandadi and T. Erik Mirkov

This chapter begins the consideration of the basic biology that is the foundation of crop-plant improvement by describing genetics, heredity, and molecular biology. The basics of DNA, RNA, and protein synthesis are necessary to an understanding of genes and how/when/where they are expressed; a crucial prerequisite for crop improvement. Gene expression encompasses all the steps from transcription of the DNA to the formation of the final protein. The chapter looks at mutations, which are the basis of polymorphism in the DNA, leading to polymorphism in the individuals of a population. Plant breeders are interested in understanding which polymorphism is associated with which trait. The chapter then highlights the importance of genome sequencing, bioinformatics, and gene editing technologies for plant biologists and breeders.

Chapter

Cover Plants, Genes & Agriculture

From Classical Plant Breeding to Molecular Crop Improvement  

Paul Gepts and Todd Pfeiffer

This chapter addresses plant breeding, where humans deliberately make crosses and choose specific plant varieties with characteristics that are desirable for food, feed, fibre, and fuel production. Crop improvement requires a never-ceasing pursuit of genetic diversity to introduce new alleles and new gene combinations into elite cultivars. This diversity originates in a wide range of sources, including other cultivars, landraces, wild progenitors, other crossable species, and transgenes. Plant breeding is a well-established science that, since the 1930s, has adopted approaches aimed to increase the efficiency of selection. These approaches include the use of quantitative genetics, artificial mutagenesis, and marker-assisted selection. More recent tools include genome-wide association studies, genomic selection based on extensive genome sequencing, and high-throughput phenotyping.