Biological pigment general, contain six ubiquitous carotenoids: neoxanthin, violaxanthin, antheraxanthin, zeaxanthin, lutein and β-carotene. Lutein is a yellow pigment found in fruits and vegetables and is the most abundant carotenoid in plants. Lycopene is the red pigment responsible for the color of tomatoes. Other less common carotenoids in plants include lutein epoxide (in many woody species), lactucaxanthin (found in lettuce), and alpha carotene (found in carrots). In cyanobacteria, many other carotenoids exist such as canthaxanthin, myxoxanthophyll, synechoxanthin, and echinenone. Algal phototrophs such as dinoflagellates use peridinin as a light harvesting pigment. While carotenoids can be found complexed within chlorophyll-binding proteins such as
Labrador Retriever coat colour genetics the colour of the dark pigment, eumelanin, and is referred to as the B (brown) locus. The variation displayed by this locus is observed in many mammals, reflecting a so-called 'dilution', a lightening, of black eumelanin to a brown colour. Initial genetic research excluded a role for the melanocortin 1 receptor and the "Agouti" locus as being the cause of the black dilution trait in dogs. Instead, TYRP1 (tyrosine related protein 1) was found to be responsible. This enzyme is localised to melanosomes, the cellular organelles that produce and store pigments, and serves to catalyze oxidation of eumelanin precursors. In