section_path: Plants/Changes to plant genome
section_name: Changes to plant genome
paragraph_text: Changes to plant genome
  
  During domestication, crop species undergo intense artificial selection that alters their genomes, establishing core traits that define them as domesticated, such as increased grain size. Comparison of the coding DNA of chromosome 8 in rice between fragrant and non-fragrant varieties showed that aromatic and fragrant rice, including basmati and jasmine, is derived from an ancestral rice domesticate that suffered a deletion in exon 7 which altered the coding for betaine aldehyde dehydrogenase (BADH2). Comparison of the potato genome with that of other plants located genes for resistance to potato blight caused by Phytophthora infestans.
  
  In coconut, genomic analysis of 10 microsatellite loci (of noncoding DNA) found two episodes of domestication based on differences between individuals in the Indian Ocean and those in the Pacific Ocean. The coconut experienced a founder effect, where a small number of individuals with low diversity founded the modern population, permanently losing much of the genetic variation of the wild population. Population bottlenecks which reduced variation throughout the genome at some later date after domestication are evident in crops such as pearl millet, cotton, common bean and lima bean.
  
  In wheat, domestication involved repeated hybridization and polyploidy. These steps are large and essentially instantaneous changes to the genome and the epigenome, enabling a rapid evolutionary response to artificial selection. Polyploidy increases the number of chromosomes, bringing new combinations of genes and alleles, which in turn enable further changes such as by chromosomal crossover.