Correct option is B
Explanation-
Mutant alleles: w¹ and w² cause white eyes. Both are X-linked and recessive. The wild-type allele is w⁺ (red eyes). The mutations are due to deletions (so non-functional alleles).
F₁ females are heterozygous: w¹/w²
F₁ females × wild-type males → male progeny should be:
(i) Half w¹/Y → white eyes
(ii) Half w²/Y → white eyes
So all males should be white-eyed, unless a rare event occurs.
Observation:
Among ~10,000 males, one had red eyes. This suggests a rare recombination or repair event, since both mutant alleles (w¹, w²) are deletions and non-functional.
Analysis of Options:
Option a - One of the mutant alleles has a high rate of spontaneous reversion - INCORRECT
Unlikely for deletions, especially large ones, to revert. Spontaneous reversion of a deletion is extremely rare, especially in both alleles.
Option b - There is an intragenic recombination between w¹ and w² during meiosis of F₁ females - CORRECT
If both alleles have different deletions, recombination between them can restore a functional gene, leading to a red-eyed male. This rare intragenic recombination event is the most plausible explanation.
Option c - There is non-disjunction of X chromosome during meiosis of F₁ females - INCORRECT
This would affect chromosome number, but not restore gene function. Also, would lead to sterile XXY or XO males, not red-eyed males.
Option d - The w¹ and w² alleles show intragenic complementation in red-eyed males though it is a rare event - INCORRECT
Intragenic complementation typically occurs in heterozygotes (i.e., in females, not males who are XY). Male has only one X chromosome, so complementation between alleles on the same gene is not possible.
Correct Answer: Option b
