Ahorticulturalist wants to produce geraniums with specific characteristics. she knows that the trait of red flowers is governed by the allele r (rr and rr) and the trait of white flowers is governed by the allele r (rr). the horticulturalisst has a red geranium with an uncertain genetic makeup. she crosses it with a white geranium (rr) and gets a generation in which half of the plants have red flowers and have white flowers. what does this combination of offspring tell her about the genetic makeup of the red geranium parent?