Flower color in snapdragons results from the amount of the pigment anthocyanin in the petals. Red flowers are produced by plants that have full anthocyanin production, and ivory-colored flowers are produced by plants that lack the ability to produce anthocyanin. The allele An1 has full activity in anthocyanin production, and the allele An2 is a null allele. Dr. Ara B. Dopsis, a famous genetic researcher, crosses pure-breeding red snapdragons to pure-breeding ivory snapdragons and produces F₁ progeny plants that have pink flowers. He proposes that this outcome is the result of incomplete dominance, and he crosses the F₁ to test his hypothesis. What phenotypes does Dr. Dopsis predict will be found in the F₂, and in what proportions?

Question

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next question. If we cross white, dominant, ally A and red, recessive A flowers and the offspring followed codominance. What color can we expect among heterozygous offspring? Choice A is white. Choice B pink, choice C white and red patches or choice D red. Well, to answer this question, we'd want to recall what codominance is and that is when both alleles are inherited, both traits are expressed together in the phenotype. So that means what we're gonna expect in this case is that if our offspring is heterozygous, so has inherited the white and red alleys. We'd expect to see choice C white and red patches. Both the white and red expressed together in the phenotype. We might be a little confused and think the answer is choice be pink. But that would be a case of incomplete dominance in which heterozygous show an intermediate phenotype different from either parent. So in that case, uh pink, in the case of incomplete dominance where you'd see this intermediate color, not the same as either parent as opposed to codominance where you see the parental phenotypes just expressed together. So that's why choice B, pink is not our correct answer. So it's always good to keep codominance and incomplete dominance straight because it's a little easy to mix them up. Choice A white is incorrect because that would be an example of complete dominance where you would only see the dominant trait expressed in the phenotype. The recessive one would be completely masked. So that's why choice A is incorrect. And of course, choice D red would be an expression of the recessive phenotype over the dominant phenotype and you just wouldn't see that. So again, if we cross white and red flowers and the offspring followed codominance, what color can we expect among heterozygous offspring? And the answer is choice C white and red patches. See you in the next video.

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Key Concepts

Incomplete Dominance

Alleles and Their Functions

Punnett Square and Phenotypic Ratios