Genetic analysis: Gene interactions In Mimulus cardinalis, two genes Y and R affect flower colour. Neither Y or R is completely dominant over the mutant alleles y and r. The two alleles of the two genes interact to produce 7 different flower colours: YY RR gives crimson flowers; Yy RR = magenta; YY Rr = orange-red; Yy Rr = magenta-rose; YY rr = yellow; Yy rr = pale yellow and all three combinations (RR, Rr and rr) with yy are white A crimson-flowered plant (YY RR) was crossed to a white flowered plant (yy rr). 1. What will be the genotype and colour of the flowers in the F1? Crimson YY RR x White yy rr. Taking into account co-dominance and dosage effects: All F1 will be magenta-rose (Yy Rr) 2. The F1 plant was selfed to produce an F2 generation. Use a Punnett Square to determine the ratio of different flower coloured plants in the F2 generation. YR Yr y R yr YR YY RR YY rR yY RR yY rR Y r YY Rr YYrr yY Rr yY rr y R Yy RR Yy rR yy RR yy rR yr Yy Rr Yy rr yy Rr yy rr From the F2 genotypes, the phenotypic ratio will be: 1 crimson : 2 magenta : 2 orange-red : 4 magenta-rose : 1 yellow : 2 pale yellow : 4 white
3. What colour flowers would be produced when F1 plants are backcrossed to their crimson parent? You may find it helpful to use a Punnett square. YR YR YR YR YR YY RR YY RR YY RR YY RR Yr YY Rr YY Rr YY Rr YY Rr y R Yy RR Yy RR Yy RR Yy RR yr Yy Rr Yy Rr Yy Rr Yy Rr F1 Yy Rr x crimson YYRR 1:1:1:1 crimson YY RR : magenta Yy RR: orange-red YY Rr : magenta rose Yy Rr 4. From the interactions of these two genes, what can you deduce about the biosynthetic pathway that leads to the final flower colour? Y/y R/r white yellow crimson