Purple is dominant to white. A heterozygous purple flower is crossed with a white flower. What are the genotypes and phenotypes of the offspring?

• A. 50% Pp (purple); 50% pp (white)
• B. 100% Pp purple
• C. 50% PP; 50% pp
• D. 25% PP; 75% Pp

Answer: (A)

When a dominant allele determines the trait, a heterozygous parent can pass on either the dominant or recessive allele to each offspring, while a homozygous recessive parent can only pass the recessive allele. Here, purple is dominant (P) over white (p), and the purple parent is heterozygous (Pp) while the white parent is homozygous recessive (pp). So each offspring gets a P or a p from the purple parent and a p from the white parent, yielding genotypes Pp or pp in equal chances. That means half of the offspring will be purple (Pp) and half will be white (pp). The purple phenotype appears in the Pp individuals because the dominant P masks the recessive p, while the pp individuals show the white phenotype. Therefore, the offspring are 50% Pp purple and 50% pp white.