Botany online 1996-2004. No further update, only historical document of botanical science!
Both the products of the gene loci C (ochre) and A (green) have a part in the pigmentation. A dominant C-locus leads to a pigmented seed coat (red, topmost row (1)). If a Ds-element (pink) is integrated into the C-gene then is the latter inactivated. As a consequence are colourless seed coats developed (yellow, second row (2)).
Rows at the bottom (3): Seed coat development starts with an integrated Ds-element but in the course of ontogenesis is Ds removed by Ac (light blue) in several cells reactivating C. The clones that develop from these cells are pigmented. As a result looks the seed coat speckled.
The spm-system (suppressor - mutator) and its influence on the expression of A (green). The A-gene, too, is needed for pigment production (row 4). If it is preceded by a defect spm-element (light grey) the transcription rate is lowered and the seed coat is only pigmented faintly (row 5). Rows at the bottom (6): In case that the first part of an intact spm-element (dark grey -grey) is located in front of an A-gene, no pigment is generated. The addition of the back part (mutator) inactivates the suppressor, the A-gene becomes active again and pigment is produced (mosaic pattern). (according to N. FEDOROFF, 1984)