Answer:
Tallness allele is dominant over dwarfness allele and purple allele is dominant over white allele.
Step-by-step explanation:
Tall, white flowering plant DDww was mated with dwarf, purple flowering plant (ddWW).
DDww x ddWW
Offspring: all DdWw (tall and purple)
Since all the offspring appeared tall and purple, it means that the tallness allele (D) is dominant over the dwarfness allele (d) while the purpleness allele (W) is dominant over the whiteness allele (w). Both d and w are said to be recessive.
In a trait that is defined by dominant/recessive alleles, the dominant allele always masks the expression of the recessive allele.