AFLP
See amplified fragment length polymorphism.

Ag
See antigen.

Agarose gels
A polysaccharide gel used to measure the size of nucleic acids (in base or base pairs) See “Gel Electrophoresis”. This is the gel of choice for DNA or RNA in the range of thousands of bases in length, or even up to 1 megabase if you are using pulsed filed gel ectrophoresis.

Agricultural biological diversity
See agrobiodiversity.

Agrobacteriurn
A genus of bacteria that includes several plant pathogenic species, causing tumour-like symptoms. See Agrobacterium tumefaciens; crown gall; hairy root culture; Ri plasmid Ti plasmid.

Agrobacteriurn tumefaciens
A bacterium that causes crown gall disease in some plants. The bacterium infects a would, and injects a short stretch of DNA into some of the cells around the wound. The DNA comes from a large plasmid - the Ti (tumour induction) plasmid - a short region of which (called T-DNA, = transferred DNA) is transferred to the plant cell, where it causes the cell to grow into a tumour-like structure. The T-DNA contains gene which inter alia allows the infected plant cells to make two unusual compounds, nopaline and octopine, that are characteristic of transformed cells. The cells form a gall, which hosts the bacterium. This DNA-transfer mechanism is exploited in the genetic engineering of plants. The Ti plasmid is modified so that a foreign gene is transferred into the plant cell along with or instead of the nopaline synthesis genes. When the bacterium is cultured with isolated plant cells or with wounded plant tissues, the "new" gene is injected into the cells and ends up integrated into the chromosomes of the plant.

Agrobacterium tumefaciens-mediated transformation
A naturally occurring process of DNA transfer from the bacterium A. tumefaciens to plants.

Agrobiodiversity; agricultural biological diversity
That component of biodiversity 'that is relevant to food and agriculture production. The term agrobiodiversity encompasses within-species, species and ecosystem diversity. (Based on FAD, 1999)