The ratio of purple to white flowers would be 3:1. Let A be dominant allele and a recessive allele. The genotypes (and their phenotypes) will be: AA (purple flowers), Aa (purple flowers), and aa (white flowers). In a cross of two heterozygous purple flowers (Aa x Aa), the offspring will be as following: 1 AA (purple flowers), 2 Aa (purple flowers), and 1 aa (white flower). In other words, there will be 3 purple flowers and 1 white flower.