In pea plants, flower color and stem height are each controlled by a single gene. For flower color, purple flowers (P) are dominant and white flowers (p) are recessive. For stem height, tall stems (T) are dominant, and short stems (t) are recessive. You perform repeated crosses between a tall purple-flowered plant and a short white-flowered plant, which produce thousands of offspring, all of which are tall purple-flowered plants. What is the genotype of the tall purple-flowered parent plant?