Question

When Bridges crossed a white-eyed female with a red-eyed male, unexpectedly 5% of females had white eyes. What phenotype explains this?

Answer 1

Crossing a white-eyed male with a heterozygous red-eyed female will result in 50% of male offspring with hemizygous white eyes, 50% of male offspring with hemizygous red eyes, 50% of female offspring heterozygous with red eyes, and 50% of female offspring homozygous with white eyes.

Step-by-step explanation:

When a white-eyed male is crossed with a female that is heterozygous for red eye color, the resulting ratio of offspring phenotypes is related to the inheritance pattern of X-linked traits. In fruit flies (Drosophila), the eye color gene is located on the X chromosome, and red eye color (W) is dominant over white eye color (w).

Since males are XY, they have only one allele for X-linked traits, so a male with a white eye allele (w) will display white eyes. Females have two X chromosomes, so a female with one red (W) and one white (w) eye allele will display red eyes but can pass either allele to her offspring.

The expected outcome for this cross would be:

• 50% of the males will inherit the white eye allele from their heterozygous mother, making them hemizygous recessive with white eyes.
  
  
• The other 50% of males will inherit the red eye allele from their mother, making them hemizygous dominant with red eyes.
  
  
• 50% of the females will inherit the white eye allele from their father and the red eye allele from their mother, making them heterozygous with red eyes (due to the dominance of the red eye allele).
  
  
• The remaining 50% of females will inherit the white eye allele from both parents, making them homozygous recessive with white eyes.