Two or more independent genes can work together to create a specific phenotype, which is known as complementary gene interaction. Bateson and Punnett crossed white and purple flowered Lathyrus plants and observed both flower colors in a 9:7 ratio in the F2 generation, showing complementary gene action. When recessive alleles at one gene locus prevent expression of alleles at another locus, it is known as dominant epistasis, which results in a phenotypic ratio of 12:3:1.

1. Non allelic gene interaction

3. Complementary gene interaction (9:7)
• Here two or more independent genes present on same loci or different
work together to create a specific phenotype.
• They are called complementary because they cannot express without
each other.
• Bateson and Punnett crossed Lathyrus odoratus. The white flowers of
Lathyrus is represented by both CCpp and ccPP genes. When they were
crossed, in F1 generation (CcPp) all plants produced purple flowers.
• The F2 generation was raised and both purple and white flowers were
obtained at a ratio of 9:7.

7. (13: 3)

9. (15: 1)

11. Epistasis

12. Dominant epistasis 12:3: 1

13. • When recessive alleles at one locus mask the expression
of both (dominant and recessive) alleles at another
locus, it is known as recessive epistasis.
• The modified phenotypic ratio is 9:3:4.