In snapdragons, there are three flower colors: red, pink and white. A farmer crosses a heterozygous flower with a red flower. The farmer wants white flowers. Could the farmer get white flowers from this cross? If not, how could he get white flowers?
A heterozygous organism carries dissimilar alleles for the same gene. Homozygous organisms contain similar allele pairs. Before crossing snapdragons, it is important to understand the allele pairings. For this example the color trait is expressed with the letter T. A homozygous TT will produce a red flower. A heterozygous Tt will produce a pink flower, and the homozygous tt results in a white flower. It is also important to note that the single allele trait displayed in the snapdragon is not dominant, which allows for the pink flower when a red (T) and a white (t) allele are present. This is called incomplete dominance or partial dominance.
The Punnet squares (attached picture) show the outcomes for each cross. There are only two squares needed to answer the first question. It is not possible to get a white flower when crossing a red flower because the homozygous red will always produce a flower with some red allele distribution.
There are three ways to produce a white flower. Crossing homozygous whites will always produce white flowers. When crossing heterozygous (pink) flowers, a white flower may be produced about 25% of the time. Finally, crossing a pink and a white flower will result in half of the offspring as white flowers.
check Approved by eNotes Editorial