In snapdragons, there are 3 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, then how could he get white flowers? What are the phenotypic and genotypic ratios of their possible offspring? What type of dominance is this?

Expert Answers

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Snapdragon flower color is an example of incomplete dominance (neither allele is dominant).

When the allele is homozygous (AA) the flowers are red and when it is homozygous (aa) the flowers are white. However, when the alleles are Aa (heterozygous), the flowers are pink. This is referred to as an indeterminant trait.

Thus, if a farmer were to cross a heterozygous flower (Aa - pink) with a red flower (AA), no white flowers could be obtained, because the resulting offspring would be 50% AA (red) and 50% Aa (pink).

See the attached image for the Punnet square. 

Note that red flowers are considered the wild type in snapdragons.

In order to obtain white flower offspring, we could mate two pink flowers (Aa x Aa = AA, 2Aa, aa), or a white flower and a pink flower (aa x Aa = 2Aa, 2aa). 

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