Index >> Genetic Interaction >> Complementary Genes or Duplicate Recessive Genes (9:7)

The F₁ plants when self-pollinated or crossed among themselves, produced the F₂,  generation with the phenotype ratio of 9 coloured and 7 white flowers. These surprising results could be understood by analysing the mechanism of colour production in flowers. A given enzyme (genetically controlled as to absence or presence in a given individual) acts upon chromogen (a colourless colour base whose absence or presence is also genetically controlled) to produce the purple or red colour of flowers. The dominant allele or alleles (CC or Cc) of gene C are responsible for the presence of chromogen, while the homozygous recessive alleles (cc) of this gene are responsible for the absence of chromogen. Likewise the dominant alleles of gene E in homozygous (EE) or heterozygous (Ee) conditions caused, production of an enzyme which is necessary for colour production from chromogen, while homozygous recessive (ee) condition does not produce any such enzyme. The appearance of 9 : 7 ratio besides 9.: 3 : 3 : 1 ratio from the cross of two white flowered sweet pea plant (CC eexcc EE).