Question

(1) The hardy geranium, Geranium lanuginosum, is native to the Himalayas and is widely cultivated due to its brilliant blue flowers, but flowers can be dark blue, light blue, speckled blue, and white. You have identified 2 genes involved in flower color. The alabaster gene catalyzes the conversion of a colorless precursor into a light blue pigment. The amount of pigment that is produced is determined by the number of functional copies of the alabaster gene. Normally, the pigment is then deposited evenly along the surface of the flower's petals due to the punctunm gene product. Without any functional punctum gene products, the pigment is instead deposited in spots which gives a speckled appearance. When the pigment is deposited in spots, it is not possible to differentiate between dark blue and light blue coloration. (a) What are the possible genotypes of the 4 color phenotypes in G. lanuginosum? (i.e, Predict the phenotypes of all allelic combinations). (2 points (b) You cross a true-breeding white Geranium with a true-breeding speckled blue-flowered plant. The offspring all have light blue flowers. If you intercross these F1 plants, what are the predicted ratios of the offspring in the F2 generation? (4 points) (c) You find another true-breeding variety of white-flowered plants and cross it against the same true- breeding speckled variety from above. This time the offspring all have speckled flowers. If you intercross these plants, what phenotypic ratios would you expect to observe in the F2 generation? (4 points)

Answer 1

• alabaster gene controls color formation.
• alabaster gene AA or Aa.....color flowers
• diluted (A) is dominant over non diluted (a)
• so A is dominant over a
• aa.......is non diluted with more blue color
• Aa... diluted light blue flower
• AA........ no color.........white
• white flower...........rrAA (white)
• dark blue flower..............RRaa (non diluted blue)
• light blue flower...........RRAa (diluted blue)
• White has genotypes.......rrAA, rrAa, rraa
• if speckled (both alleles for white and blue color are present)......RrAa or Rraa or RrAA
• true breeeding white geranium crossed to true breeding speckled blue
• rraa xRrAA

• 	ra
  RA	RrAa (speckled light blue)
  RA	RrAa (speckled light blue)
  rA	rrAa (white )
  rA	rrAa (white )