Question

A purple flower with an unknown genotype is crossed with a white flower. Determine the genotype of the purple flower if purple (P) is dominant and white (p) is recessive

Answer 1

Heterozygous. A diploid organism is heterozygous at a gene locus when its cells contain two different alleles of a gene.[3] The cell or organism is called a heterozygote specifically for the allele in question, and therefore, heterozygosity refers to a specific genotype. Heterozygous genotypes are represented by a capital letter (representing the dominant allele) and a lowercase letter (representing the recessive allele), such as "Rr" or "Ss". Alternatively, a heterozygote for gene "R" is assumed to be "Rr". The capital letter is usually written first.

If the trait in question is determined by simple (complete) dominance, a heterozygote will express only the trait coded by the dominant allele, and the trait coded by the recessive allele will not be present. In more complex dominance schemes the results of heterozygosity can be more complex.

Answer 2

If purple is dominant, the genotype of the purple flower could be PP or Pp, as both would give a purple colour. However, if the crossed flower turned out to be white, we could say with certainty that the genotype of the purple flower is Pp as the genotype of the white crossed flower would be pp, which would not be possible if the purple flower's genotype was PP.