Carotenoids are a group of pigments found in many plant species. They are formed
ID: 167626 • Letter: C
Question
Carotenoids are a group of pigments found in many plant species. They are formed via the terpenoid pathway. Lycopene (Lyc) is a red colored pigment, carotene (Car) is orange and Lutein (Lut) yellow. The precursor molecules are colorless. See figure 1. a. Red flower color in Coneflowers is dominant to white. (1pt) i. What symbols would you use to represent the genotypes of a heterozygous red flowered plant and a white flowered plant? ii. What would the expected phenotypic ratios be in a cross of these parents? b. Red flowered cone flowers x white flowered ones leads to yellow flowered coneflowers. What would explain this, that is how would genotype link to phenotype – look at the figure? (2pts) c. It is actually easier to map this as a two-locus interaction (see Labradors in the book). If you crossed F1 plants that were heterozygous at both loci, what would the genotypes and phenotypes be in a population of 100 progeny? (3pts) d. Would it be possible to have orange flowered coneflowers? If so, would they be dominant or recessive?
Phy Enzyme 1,2 PDs Lyc Enzyme 3 L-cyclase Car Enzyme 4,5 Hydroxylase LutExplanation / Answer
The given information is: Lycopene (Lyc) is a red colored pigment, carotene (Car) is orange and Lutein (Lut) yellow. The precursor molecules are colorless. See figure 1. a. Red flower color in Coneflowers is dominant to white.
Answer a) i) The symbol should be Rr X rr
Where, “R’ is the symbol for ‘red’ and ‘r’ is the symbol for ‘white’.
Answer a) ii)
The expected phenotypic ratio will be 1(red):1(white)
Answer b) Red flowered cone flowers (R_) x white flowered (rr) ones leads to yellow flowered coneflowers.
Explanation: This shows that apart from gene ‘R’; there is one more gene in the parents which is present in recessive form.
So, the genotype of red flower will be “RRyy”. The ‘R’ gene is responsible for red color. Since ‘y’ gene is in recessive form, its color is not there.
White flower is having the genotype “rrYY”. ‘Y’ gives yellow color in presence of ‘R’. In absence of ‘R’, the color will be white.
On crossing these two parents, the result will be ‘RrYy’ (yellow). This means that “Y” is epistatic over ‘R’; or yellow color masks the effect of red color. This is an example of dominant epistasis.
Answer c) Crossing of heterozygous F1 plants:
RrYy X RrYy
Result: R_Y_ will be yellow = 9/16
R_yy will be red = 3/16
rrY_ will be white = 3/16
rryy will be white = 1/16
So, the phenotypic ratio should be 9:3:4
Answer d) Appearance of orange color means that one more gene is there.