They don't have to be orange, carrots can come in a wide variety of colors derived from several different pigments. Upper left is a conventional "orange" carrot. The color is due mainly to beta-carotene, with some alpha-carotene, both of which are orange pigments.Center left is a "yellow" carrot, whose color is due mainly to xanthophylls (a type of carotene). Bottom left is a "red" carrot, due mainly to lycopene (another type of carotene, also found in tomatoes), in addition to some beta- and alpha-carotene. Upper right is a "purple" carrot, due to pigments in an entirely different class, the anthocyanins. Lower right is a "white" carrot, the color of a carrot with none of these pigments. Click here for a larger version (380x560) 164kb Click here for a high resolution version (2460x3348) 559kb
Root color genes -- P1, Y, L.
Darker Purple - Variation in anthocyanin pigments occurs naturally in carrots. Classical breeding methods are being used to cross some of these types, and select the darkest purple carrots with higher levels of pigments.
'A Plus' New darker-orange varieties of carrots have been produced by the breeding program. This picture shows one USDA Carrot Variety, 'A Plus', which is high in carotene levels.
Carrot breeding - Small (left) and large (right) isolation cages which are used for controlled crossing of one or more carrot plants.
Carrot breeding
Left: one small isolation cage used for controlled pollination of carrots. (click on photo for larger version)
Right: Inside the carrot isolation cages. Bees are pollinating the carrot flowers.
Root sugar gene Rs - This single gene in carrot controls the type of sugar in the root.
Sucrose is a disaccharide, composed of one molecule of fructose attached to one molecule of glucose. Fructose and glucose are reducing sugars, and sucrose is a non-reducing sugar. Thus, the gene name Rs stands for reducing sugar.
When this dominant allele (Rs) is present, the carrot root will accumulate the reducing sugars fructose and glucose. When both recessive alleles (rsrs) are present, the carrot root will accumulate primarily sucrose.
These graphs show the distribution of sugar types when a low reducing sugar type rsrs (P1) was crossed with a high reducing sugar type RsRs (P2), producing a hybrid offspring Rsrs (F1). Because Rs is dominant, the F1 resembles P1.
A backcross of the F1 with P2 (designated BC1P2) is half RsRs and half Rsrs, both of which are high reducing sugar types.
The F1 selfed (F2) should show a 3:1 segregation, due to the distribution of the three possible genotypes 1:RsRs, 2:Rsrs, 1:rsrs.
Garlic Pictures
Garlic true seed production - this plant was produced from a true seed of garlic, a rare event, since cultivated garlic has been exclusively propagated vegetatively for many hundreds of years.
Garlic coat of arms, 1450-1500, Germany
Garlic, Allium sativum, from the book Hortus Sanitatis, Mainz, 1485.
Printable Version
E-mail this page
