Video Transcript
Snapdragon flowers (pictured) show
incomplete dominance in the color of their petals. The petals can be red, CR CR white,
CW CW, or pink, CR CW. Two pink flowers are crossed. What is the probability, in
percent, that their offspring will also have pink flowers?
Let’s start by annotating our
diagram with the information given to us in the question. We are told that the genotype of
red snapdragons is CR CR. The C means color and the R means
red. Remember, the set of alleles an
organism possesses for a characteristic is their genotype. We are also told that the genotype
of white snapdragon flowers is CW CW, where this time the superscript W means
white. Finally, we know that the genotype
of pink snapdragon flowers is CR CW.
The phenotype is the observable
trait that is produced by the genotype. In these cases, the phenotype of
each individual plant is its flower color, red, white, or pink. The question states that the
inheritance of flower color in snapdragons shows incomplete dominance. Allele show in complete dominance
when an intermediate phenotype is created in an organism that is heterozygous for a
particular trait, which means that they have one of each allele. In this example, the intermediate
phenotype is the pink flower color, as it is a blend between the white and red
flowers and has a heterozygous genotype.
Let’s draw a Punnett square to work
out the percentage of offspring likely to be pink when these two parent plants with
pink flowers reproduce. Punnett squares like this one are
used to visually represent how alleles are inherited and predict the genotypes and
phenotypes of the offspring produced by crossing parents with known genotypes. We know that pink snapdragons have
the genotype CR CW. We put the alleles that will be
present in one parent’s gametes in the top row and we put the alleles that will be
present in the other parent’s gametes in the left column.
Now we need to fill in the blank
cells with the potential offspring genotypes that are able to be produced from a
cross between these two pink parents. We do this by taking the alleles in
the gametes from each row and column head, for example, the CR allele from this
parent and the CR allele from this other parent. Let’s do this for the rest of the
cells. We can see in the Punnett square
that one out of four of the offspring has the genotype CR CR and so has a
red-flowered phenotype. We can also see that one out of
four of the offspring has the genotype CW CW and so a white-flowered phenotype. Finally, two out of the four
offspring produced in this cross have the heterozygous genotype CR CW and so have a
pink-flowered phenotype.
The question asks us to determine
the probability in percent that the offspring produced by this cross will have pink
flowers. So let’s do this by converting this
value into a percentage by multiplying it by 100 percent. Therefore, the probability that the
offspring produced by two pink snapdragons will also be pink is 50 percent.
