Wild type fruit flies have red eyes. A white-eyed female fly is crossed with a red-eyed male fly. All of the females from the cross are red-eyed and all of the males, white-eyed. What type of inheritance pattern is this?

• A. Autosomal recessive.
• B. Autosomal dominant.
• C. Sex-linked on X chromosome.
• D. Incomplete dominance.
• E. Sex-linked on Y chromosome

Answer: (C)

Verified step by step guidance

1. Identify the phenotypes of the offspring: All females are red-eyed, and all males are white-eyed.
2. Consider the inheritance pattern: Since the trait is different between males and females, it suggests a sex-linked pattern.
3. Determine which chromosome the trait is linked to: In fruit flies, sex-linked traits are often on the X chromosome because males have only one X chromosome (XY) and females have two (XX).
4. Analyze the parental genotypes: The white-eyed female must be homozygous recessive (X^wX^w), and the red-eyed male must have a dominant allele on his X chromosome (X^RY).
5. Explain the inheritance: Females receive one X chromosome from each parent, so they inherit the dominant red-eye allele from the father, while males inherit their single X chromosome from the mother, resulting in white eyes. This confirms the trait is sex-linked on the X chromosome.