A plant can produce either purple flowers or white flowers. The purple flower color is dominant over the white flower color. What is the ratio of the offspring with purple flowers to the total number of offspring if two plants that are heterozygous for purple flowers are crossed?

Let P represent the dominant purple allele and p the recessive white allele. Crossing two heterozygous plants (Pp × Pp) gives offspring genotypes PP, Pp, Pp, and pp. Three of the four have at least one dominant P allele and therefore have purple flowers, so the ratio is 3:4, choice C.

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