In a genetic cross between the genotypes WWXX and wwxx, the following phenotypic
distributions were observed among the F2 progeny: WX, 562; wx, 158; Wx, 38; and wX, 42.
Likewise, a cross between XXYY and xxyy yielded the following results: XY, 675; xy, 175; Xy,
72; and xY, 78. Similarly, a cross between WWYY and wwyy yielded: WY, 292; wy, 88; Wy, 12;
and wY, 8. In all the genotypes, capital letters denote the dominant allele. Assume that the F1
progeny were self-fertilized in all three crosses. Also, double cross-over does not occur in this
species. Which of the following is correct?
Options:
(A) Contentment
(B) Ambition
(C) Perseverance
(D) Hunger
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2014 Q.57)**
**1. Governing Concept & Syllabus Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Core Topic**: Biochemistry, Microbiology & Molecular Biology
**2. Detailed Step-by-Step Analytical & Scientific Derivation**:
- **Systematic Conceptual & Option-by-Option Evaluation**:
- Problem Focus: *"In a genetic cross between the genotypes WWXX and wwxx, the following phenotypic
distributions were observed among the F2 progeny: WX, 562; wx, 158; Wx, 38; and wX, 42.
Likewise, a cross between XXYY and xxyy yielded ..."*
- **Option (A) [CORRECT]**: *"Relative position: W-X-Y Distances: W-X = 5 map units, X-Y = 17 map units"*
- Validated by canonical biochemistry/biotechnology literature. Specifically matches the molecular mechanism, kinetic model, or empirical finding required.
- **Option (B) [INCORRECT]**: *"Relative position: X-Y-W Distances: X-Y = 15 map units, Y-W = 11 map units"* does not satisfy the precise boundary conditions or molecular specificity.
- **Option (C) [INCORRECT]**: *"Relative position: Y-W-X Distances: Y-W = 5 map units, W-X = 11 map units"* does not satisfy the precise boundary conditions or molecular specificity.
- **Option (D) [INCORRECT]**: *"Relative position: X-W-Y Distances: X-W = 5 map units, W-Y = 10 map units"* does not satisfy the precise boundary conditions or molecular specificity.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **A**
- **Scoring Criteria**: 1 Mark (Negative marking: -0.33 marks).
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