A heterozygous trait contains two different allelic forms of a gene in which one is a dominant allele and one is recessive allele. If there is a crossing between two plants that are heterozygous for their trait then the probability of expression of the dominant allele is 3/4.
So according to this question plants are heterozygous that means the genes would be like Pp and Pp. Here P indicates the purple color allele which is dominant and p indicates recessive white color allele.
Therefore cross between these two will give genotypes PP, Pp Pp, and pp. So according to the law of dominance that says dominant allele will express itself, therefore, probability of purple-flowered offspring is 3/4 because 3 out of four genotypes have the dominant allele.
