Video Transcript
The flower color of snapdragon plants shows incomplete dominance. C R indicates red flowers and C W indicates white flowers. Complete the Punnett square provided and state the probability, in percent, of the offspring inheriting pink flowers.
The question states that the flower color in snapdragon plants shows incomplete dominance. Incomplete dominance is one example of when one allele for a trait does not have complete dominance over another. So when an organism is heterozygous for a trait, which means that they have one of each allele that control it, the two traits combine into an intermediate blended phenotype. The question tells us that there’re three potential phenotypes for this flower color trait in snapdragon plants, red flowers, white flowers, or they can have pink flowers.
When an allele that codes for red flowers and an allele that codes for white flowers are both present in the genotype, this gives the organism a heterozygous genotype of C R C W. Given that the snapdragons show incomplete dominance for this trait, we can assume that when they have this heterozygous genotype that their flower color will be a blend between white and red, which is pink flowers. Let’s have a look at the Punnett square that we’ve been given.
Punnett squares visually represent how alleles are inherited and predict the genotypes and phenotypes of offspring produced by crossing parents with known genotypes. The gametes of the red-flowered parent are shown in the top row of the Punnett square here, and we can tell as each contains a superscript R for red. This parent is homozygous for the red trait, as they have two of the same alleles in their genotype. The gametes of the white-flowered parent are shown in the left-hand column here of the Punnett square, and we can tell as each contains a superscript W, which stands for white. This parent is also homozygous but for the white trait.
Remember, the uppercase C that precedes each superscript letter stands for color, and it shows that this pattern of inheritance of flower color does not show complete dominance. Let’s fill in the blank cells of the Punnett square, which represent the offspring’s potential genotypes, by using the alleles from the gametes from each row and column head. For example, the first blank cell will contain one C R allele from this parent and one C W allele from this parent.
The cells we have just filled in represent the potential genotypes of the offspring that could be produced by a cross between these two parents. And you might have noticed that they are all C R C W. This means that all of the offspring in this cross are heterozygous for this trait, as they have one allele coding for red flowers and one allele coding for white flowers.
As this trait shows incomplete dominance, the combination of the red and white coding alleles produces a new intermediate phenotype, which is pink flowers. As the question asks for the probability in percent of the offspring inheriting pink flowers, let’s convert this fraction into a percentage by multiplying it by 100 percent. Therefore, the probability that the offspring will inherit pink flowers is 100 percent.
