The triangle of U ( ) is a theory about the evolution and relationships among the six most commonly known members of the plant genus Brassica. The theory states that the genomes of three ancestral diploid species of Brassica combined to create three common tetraploid vegetables and oilseed crop species. It has since been confirmed by studies of DNA and proteins. The theory is summarized by a triangular diagram that shows the three ancestral genomes, denoted by AA, BB, and CC, at the corners of the triangle, and the three derived ones, denoted by AABB, AACC, and BBCC, along its sides. The theory was first published in 1935 by Woo Jang-choon, a Korean-Japanese botanist (writing under the Japanized name "U Nagaharu"). Woo made synthetic hybrids between the diploid and tetraploid species and examined how the chromosomes paired in the resulting triploids. U's theory The six species are The code in the "Chr.count" column specifies the total number of chromosomes in each somatic cell, and how it relates to the number of chromosomes in each full genome set (which is also the number found in the pollen or ovule), and the number of chromosomes in each component genome. For example, each somatic cell of the tetraploid species Brassica napus, with letter tags AACC and count "2=4=38", contains two copies of the A genome, each with 10 chromosomes, and two copies of the C genome, each with 9 chromosomes, which is 38 chromosomes in total. That is two full genome sets (one A and one C), hence "2=38" which means "=19" (the number of chromosomes in each gamete). It is also four component genomes (two A and two C), hence "4=38". The three diploid species exist in nature, but can easily interbreed because they are closely related. This interspecific breeding allowed for the creation of three new species of tetraploid Brassica. (Critics, however, consider the geological separation too large.) These are said to be allotetraploid (containing four genomes from two or more different species); more specifically, amphidiploid (with two genomes each from two diploid species). Further relationships The framework proposed by U, although backed by modern studies, leaves open questions about the time and place of hybridization and which species is the maternal or paternal parent. B. napus (AACC) is dated to have originated about 8000 or 38000–51000 years ago. The homologous part of its constituent chromosomes has crossed over in many