A certain red-flowered plant is self-fertilized. The progeny are 131 white-flowered plants and 169 red-flowered plants. Give a genetic explanation for these observations.

Ratio of red flowers: white flowers = 169: 131 = 9: 7  as given in the question. It is clear that the color is possible only by at least 2 genes.

Let assume genes are A and B.

Now the cross AaBb (Red) x AaBb (Red)

Gametes > AB Ab aB ab AB Ab aB ab

   AB              Ab                     aB             ab

AB AABB (Red)AABb (Red)AaBB (Red)AaBb (Red)

Ab AABb (Red)AAbb (White)AaBb (Red)Aabb (White)

aBAaBB (Red)AaBb (Red)aaBB (White)aaBb (White)

abAaBb (Red)Aabb (White)aaBb (White)aabb (White)

The ratio of Red flowers: White flowers is 9:7

The red color flower is produced when both the alleles of genes are dominant. if any of the alleles of genes is recessive, it will produce the white color flower. This is one of example complementary gene interaction where the presence of both genes in the dominant form complements each other to produce red color flowers.