Section 3: Genetics, Cellular and Molecular Biology
Classical Genetics and Epistasis
Subtopic: Mendelian Genetics & Gene Interactions
Question Statement:
In a genetic study, 80 people were found to have alleles for polydactyly. Only 36 of them were
polydactylous. What is the extent of penetrance percentage? ________
Official Answer Key:
45 to 45
Step-by-Step Solution & Explanation
### **Step-by-Step Solution & Mathematical Derivation (GATE BT 2013 Q.44)**
**1. Governing Concept & Definition**:
- **Topic**: Classical Genetics & Penetrance
- **Penetrance** is the percentage of individuals with a given genotype who exhibit the associated clinical phenotype:
$\text{Penetrance} = \frac{\text{Number of individuals expressing phenotype}}{\text{Total individuals with genotype}} \times 100\%$
**2. Detailed Step-by-Step Calculation**:
- **Given**:
- Individuals possessing polydactyly alleles $= 80$
- Individuals exhibiting polydactyly phenotype $= 36$
- **Penetrance Calculation**:
$\text{Penetrance} = \frac{36}{80} \times 100\% = \frac{9}{20} \times 100\% = 45\%$
**3. Final Answer**:
- **Calculated Value**: **45%**
- **Official GATE Accepted Range**: **45 to 45**
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