Q.97 A cross is made between a white eyed-miniature winged female with a red eyed-normal winged
male of Drosophila melanogaster. Further crossing of F1 female offspring from this cross with a
white eyed-miniature winged male fly gave 95 white eyed-normal winged, 102 red eyed-miniature
winged, 226 red eyed-normal winged and 202 white eyed-miniature winged offspring in F2
generation. What is the percent frequency of recombination between the two genes?
(A) 20.11 (B) 31.52 (C) 49.10 (D) 34.12
Drosophila Recombination Frequency: White Eye-Miniature Wing Cross Analysis
This Drosophila cross involves X-linked white eye (w) and autosomal miniature wing (m) genes, with F2 data revealing linkage and recombination. The recombination frequency is 31.52%, corresponding to option (B).
Cross Setup
White-eyed miniature-winged female (X^w X^w ; m/m) crossed with red-eyed normal-winged male (X^W Y ; M/M) produces F1 females heterozygous for both (X^w X^W ; m/M). These F1 females testcrossed with white-eyed miniature male (X^w Y ; m/m) yield F2 progeny.
Parental classes dominate (226 red-normal, 202 white-miniature), confirming linkage; recombinant classes are fewer (95 white-normal, 102 red-miniature).
Recombination Calculation
Total progeny: 95 + 102 + 226 + 202 = 625.
Recombinants: white-normal (95) + red-miniature (102) = 197.
Frequency: (197 / 625) × 100 = 31.52%.
This measures single crossovers between loci; double crossovers negligible at this distance.
Option Analysis
| Option | % Value | Matches Data? | Reason |
|---|---|---|---|
| (A) 20.11 | Low | No | Underestimates; ignores full recombinant count (e.g., halves recombinants) |
| (B) 31.52 | 197/625 | Yes | Exact: recombinants/total × 100 |
| (C) 49.10 | Near 50% | No | Suggests unlinked genes; parentals would equal recombinants |
| (D) 34.12 | Close but high | No | Possible miscalculation (e.g., excluding one class); precise math yields 31.52% |
Linkage Insight
White eye is X-linked recessive; miniature wing autosomal recessive. F1 female dihybrid shows coupling phase (w m / W M). RF <50% confirms linkage, with map distance ~32 cM.
