Question

The F2 hybrid phenotypic ratio 9: 3: 4 is explained on the basis of:
A. Epistatic gene
B. Supplementary gene
C. Allelic interaction
D. Complementary gene interaction

Answer 1

Hint: It is a type of interaction wherein a dominant allele of a gene is superior to that of another gene. In this case of supplementary gene interaction, the dominant allele of one gene governs a particular character and shows that specific phenotypic effect.

Complete answer: The dominant gene of another allele does not show its effect but when it is present with the dominant gene of the other allele it modifies the phenotype.

For example, genes A and B are responsible for the fur color of mice.
AA is dominant and is responsible for the albino mice. BB is dominant and is responsible for black. In AABB, allele A is dominant over allele B, but B influences A.
This produces agouti colored mice.

	AB	Ab	aB	ab
AB	AABBAgouti	AABbAgouti	AaBBAgouti	AaBbAgouti
Ab	AABbAgouti	AAbbAlbino	AaBbAgouti	AabbAlbino
aB	AaBBAgouti	AaBbAgouti	AaBBBlack	AaBbBlack
ab	AaBbAgouti	AabbAlbino	AaBbBlack	AabbAlbino

Hence, the ratio of the fur color agouti, black, and albino is 9: 3: 4.

So the correct Option is B: Supplementary gene

Note: In genetics, an epistatic gene is a gene that determines whether or not a trait will be expressed in the phenotype.
1. Allelic interactions are examples of complex genetic interactions between the alleles of a single gene. They are also referred to as allelic or Intra- allelic interactions.
2. Non-allelic or inter-allelic interactions occur where the development of a single character is due to two or more genes affecting the expression of each other in several ways.
3. Complementary gene interactions are non allelic gene interactions (or epistasis) where dominant alleles at heterozygous loci may complement each other by masking the recessive alleles at the respective loci.