Rice, maize, wheat: few genotypes harvested, but genetic variation exists. Idea (vavilov: crops originated in areas where diversity of wild relatives is greatest. Vernalization (lysenko: apply cold treatment, induce early flowering, caused by epigenetic modification of flowering time genes, vernalization reset during meiosis, vernalized state not transmitted across generations, lysenko rejected mendelian, darwinism in favor of lamarck. Consequences: southern crops acclimatized to grow in north via lamarckian breeding. Domestication of crops: severe bottleneck: small subset chosen for cultivation, strong artificial selection: human retain best performing crops, select: germination timing, seed size, nutrition. Consequences: decreased genetic variation, ways o measure, h: average frequency of heterozygous individuals per gene locus, p : proporation of polymorphic gene loci, : average number nucleic differentiation per site. 1: future crop improvement, pest, pathogen management. Domestication of maize from teosinte: wild teosinte, domestivated maize, led to decreased variation, genetic diversity of teosinte high, genetic diversity in maize high but not 1:1.