Triangle of U

Triangle of U

The Triangle of U is a concept in botany that describes the evolutionary relationships among certain species of the genus Brassica. It was first proposed by the Korean-Japanese botanist Woo Jang-choon in 1935. The "U" in the name refers to Woo Jang-choon's family name, "U" being the Japanese reading of the character "Woo".

Diagram of the Triangle of U showing the relationships among Brassica species.

Description

The Triangle of U illustrates the genetic relationships between six species of Brassica. These species are:

• Brassica rapa (AA, 2n=20)
• Brassica nigra (BB, 2n=16)
• Brassica oleracea (CC, 2n=18)
• Brassica napus (AACC, 2n=38)
• Brassica juncea (AABB, 2n=36)
• Brassica carinata (BBCC, 2n=34)

The three diploid species, B. rapa, B. nigra, and B. oleracea, are the ancestors of the three allotetraploid species, B. napus, B. juncea, and B. carinata. The diagram shows that each allotetraploid species is derived from the hybridization of two of the diploid species.

Genetic Relationships

The Triangle of U is based on the observation that the genomes of the diploid species can combine to form the genomes of the allotetraploid species. The relationships are as follows:

• B. napus (AACC) is a hybrid of B. rapa (AA) and B. oleracea (CC).
• B. juncea (AABB) is a hybrid of B. rapa (AA) and B. nigra (BB).
• B. carinata (BBCC) is a hybrid of B. nigra (BB) and B. oleracea (CC).

These relationships are supported by cytogenetic and molecular studies, which have confirmed the chromosomal and genetic similarities among these species.

Significance

The Triangle of U is significant in the study of plant breeding and evolutionary biology. It provides a framework for understanding the genetic diversity and evolutionary history of the Brassica species, which are important agricultural crops. These species include vegetables like cabbage, broccoli, and mustard, as well as oilseed crops like canola.

Related pages

• Brassica
• Plant hybridization
• Polyploidy

References

• Woo, J. (1935). "Genomic analysis in Brassica with special reference to the experimental formation of B. napus and peculiar mode of fertilization". *Japanese Journal of Botany*.
• Prakash, S., et al. (2011). "Brassica and its close allies: cytogenetics and evolution". *Plant Breeding Reviews*.