Question

Ratio of complementary genes is
A. 9:3:4
B. 12:3:1
C. 9:3:3:4
D. 9:7

Answer 1

Hint: One of two or more genes that when present together produce effects qualitatively distinct from the separate effect of any one of them. Complementary genes are two pairs of non allelic dominant genes.

Complete answer:
 If two genes are present on different loci produce the same effect when present alone but interact to form a new trait when present together they are called complementary genes. Hence for the development of dominant character, presence of both the genes is necessary. For example, the flower colour in Lathyrus odoratus (sweet pea) is dependent upon two non allelic complementary genes C and P are essential for production of a particular or special phenotype i.e. complementary factor. When either of gene loci have homogenous recessive alleles (i.e. genotypes of ccPP, ccPp, Ccpp, ccpp) they produce identical phenotypes and change \[{F_2}\] ratio to 9:7
> 9:3:4 This ratio is obtained in case of recessive epistasis
 Example: Coat colour in mice
> 12:3:1 This ratio is obtained in case of dominant epistasis
 Example: fruit colour in Cucurbita pepo
> 9:3:3:4 This ratio is obtained in case of dihybrid cross phenotype ratio
 Example: Comb pattern in fowl
> 9:7 This ratio is obtained in case of complementary genes in \[{F_2}\] generation.
  Example: Flower colour in Lathyrus odoratus

So, the correct answer is option D.

Note: The Mendelian ratio 9:3:3:1 is changed to 9:7 due to complementation of both genes. Complementary genes were first discovered by Bateson and Punnett. Complementary genes are that both contribute to a single characteristic.