Why can purple-flowered pea plants carry an allele for white flowers?

Purple-flowered pea plants can carry an allele for white flowers because they are heterozygous for the trait of flower color, possessing one dominant allele for purple flowers (R) and one recessive allele for white flowers (r).12

In Gregor Mendel’s experiments, he discovered the phenomenon of dominance, where the purple-flower allele is completely dominant over the white-flower allele. Because of this dominance, a plant with the genotype Rr will express the purple phenotype even though it carries the genetic information for white flowers.12

These alleles do not blend or contaminate each other within the plant's genotype. Instead, they remain discrete units of heredity that segregate independently during the formation of gametes, allowing the recessive white-flower trait to reappear in subsequent generations when two recessive alleles are inherited together (rr).21