Question

Eye colour in fruitfly is a sex linked trait and the cross of white eyed female with red eyed male gives red eyed females and white eyed males. Rarely this cross may give all white eyed females and red eyed males. This was found to be due to non-disjunction of

• A. Two Y chromosomes in female fly
• B. Two X chromosomes in female fly
• C. Four Y chromosomes in male fly
• D. Four X chromosomes in male fly

Answer 1

The correct option is B Two X chromosomes in female fly

The cross of white eyed female with red eyed male gives red eyed females and white eyed males. Rarely this cross may give all white eyed females and red eyed males. This results from non-separation of two homologous X chromosomes during anaphase I of meiosis. Both X chromosomes go together to same pole resulting in formation of one gamete with XX and other with no X-chromosome. Fertilization of XX gamete with Y-sperm forms XXY (white eyed female) and fertilization of gamete with no X-chromosome to X-sperm forms red eyed males (X). This phenomenon is known as non-disjunction of two X chromosomes.

Thus, the correct answer is option B.