You are an aspiring botanist and decide to study some orchid

You are an aspiring botanist and decide to study some orchid genetics. Knowing that the pink color phenotype is an incompletely dominant phenotype, you decide to study it further. You discover that when you cross two pink orchids, you only ever obtain a phenotypic ratio of 1/3 white orchids to 2/3 pink orchids. How might you explain this phenomenon?

Solution

This can be explained from the fact that pink phenotype is produced in heterozygous condition when both allele for red colour (R) and allele for white colour (r) occurs together. The plant incompletely expresses the dominant trait (R) causing plants with the Rr genotype to express flowers with less red pigment resulting in pink flowers.

Due to this heterozygous condition, we get phenotypic ratio of 1/3 white orchids. This phenotupe is produced due to combination of recessive allele (r) on each from each parent and 2/3 pink orchids due to combination one allele for red colour (R) from one parent and allele for white colour (r) from other parent and vice versa.