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Q.
The $F _{2}$ dihybrid ratio $12: 3: 1$ is explained on the basis of
Principles of Inheritance and Variation
Solution:
When two different genes which are not alleles, effect the same trait of the organism, the expression of one covers up the expression of the other. A gene that masks or prevents the expression of another is called epistatic to it and the gene that is hidden is known as hypostatic. Such interactions give modified $F _{2}$ ratio as $12: 3: 1$.