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Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation1 Mark
Question
For question two statements are given-one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both assertion and reason are true and reason is the correct explanation of assertion.
  2. Both assertion and reason are true but reason is not the correct explanation of assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false.
Assertion: Epistasis does not show normal dihybrid ratio, i.e., 9 : 3 : 3 : 1.
Reason: A gene suppresses the phenotypic expression of a non-allelic gene.
✓

Answer

  1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

The gene which inhibits or suppresses the expression of a non-allelic gene is known as epistatic gene. Epistasis reduces the number of phenotypes appearing in the F2 generation of dihybrid cross. Thus instead of normal 9 : 3 : 3 : 1 dihybrid ratio, epistasis may result in a ratio of 9 : 3 : 4 (recessive epistasis). 12 : 3 : 1 (dominant epistasis). 13 : 3 (dominant recessive epistasis) or 9 : 7 (double recessive epistasis), etc

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