Section 3: Genetics, Cellular and Molecular Biology
Classical Genetics and Epistasis
Subtopic: Mendelian Genetics & Gene Interactions
Question Statement:
The allele associated with albinism in humans is recessive (c). The probability
that an albino male (cc) and a carrier female (Cc) will have an offspring with
normal skin pigmentation is _______ .
(Round off to one decimal place)
Official Answer Key:
0.5 to 0.5
Step-by-Step Solution & Explanation
### **Step-by-Step Solution & Mathematical Derivation (GATE BT 2025 Q.30)**
**1. Governing Concept & Definition**:
- **Topic**: Classical Mendelian Genetics & Inheritance of Autosomal Recessive Traits
- Albinism is an autosomal recessive condition denoted by allele $c$.
- Affected individual (albino): genotype $cc$
- Carrier individual: genotype $Cc$
- Normal homozygous: genotype $CC$
**2. Detailed Step-by-Step Calculation**:
- **Parents**:
- Albino male: Genotype = $cc$ (produces only gametes carrying allele $c$)
- Carrier female: Genotype = $Cc$ (produces gametes $C$ and $c$ in equal proportions, $1/2$ each)
- **Punnett Square / Cross Progeny**:
- $c \times C \rightarrow Cc$ (Carrier, normal phenotype): probability = $0.5$
- $c \times c \rightarrow cc$ (Albino, affected phenotype): probability = $0.5$
- Therefore, the probability that a child born to them will have albinism ($cc$) is $1/2 = 0.5$.
**3. Final Answer**:
- **Calculated Value**: **0.5**
- **Official GATE Accepted Range**: **0.5 to 0.5**
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