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

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation1 Mark
MCQ
For question two statements are given-one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes $\text{(a), (b), (c)}$ and $(d)$ as given below.
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.
  • A
    Both assertion and reason are true and reason is the correct explanation of assertion.
  • ✓
    Both assertion and reason are true but reason is not the correct explanation of assertion.
  • C
    Assertion is true but reason is false.
  • D
    Both assertion and reason are false.
✓

Answer

Correct option: B.
Both assertion and reason are true but reason is not the correct explanation of assertion.
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 $F_2$ 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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