Question

A purebred purple flowering plant is crossed with a purebred white flowering plant, and they produce offspring that have purple flowers. Which is the trait for purple flowers?

Answer 1

The purple is the dominate trait for the flower

Answer 2

The given case says, the pure breed purple flower is crossed with pure breed white flower. The pure breed traits are always homozygous in nature.

On crossing white and purple flower, all the  progeny have a phenotype of purple flower. In cross reproduction, the progeny inherit one allele from each parent. So, in the progeny, there would be one allele for purple and one for white, but the phenotype is purple, so, it suggest that purple trait masks the effect of white trait. Hence, the purple phenotype is dominant over white phenotype.

The given cross represent the cross between purple (PP) and white (pp) pure breeds.