A classical example of interaction of genes is the complementation between two genes meaning that both genes are necessary for the production of a particular phenotype. W. Bateson and R.C. Punnett observed that, when two white flowered varieties of sweet pea, Lathyrus odoratus were crossed, F1progeny had coloured flowers. When F2 progeny obtained from F1 was classified, plants with coloured flowers and those with white flowers were obtained in 9 : 7 ratio. This is again a modification of 9 : 3 : 3 : 1 ratio, where only one character i.e. flower colour is involved and only two classes recognized (coloured and white flowers). The abbreviated genotypic ratio given in Table 3.4 will explain the kind of interaction involved.
It is obvious in the above example that both the dominant alleles, ‘C
’ and ‘P’
are necessary for the production of pigment in the flowers. Each of the two parents lacks one of the two dominant alleles and, therefore, both bear only white flowers. The two dominants are brought together in F1
generation and therefore coloured flowers are produced.