Answer and Explanation:
Available data:
Cross: true-breeding red-eye fly bred with a true breeding white-eye fly
Parentals) RR x rr
Phenotypes) Red-eyed White-eyed
Gametes) R R r r
Punnett square) R R
r Rr Rr
r Rr Rr
F1) 4/4 = 100% of the progeny will be heterozygous for the trait expressing red eyes, Rr
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In Drosophila melanogaster, the fruit fly, the gene for the eye color is X-linked. So in this species:
- X⁺ expresses red eyes ----- > + is the dominant allele for red color
- X⁻ expresses white eyes ----> - is the recessive allele for white color
Option 1: true-breeding red-eyed females and white-eyed male
Parentals) X⁺ X⁺ x X⁻Y
Phenotypes) Red-eyed female White-eyed male
Gametes) X⁺ X⁺ X⁻ Y
Punnett square) X⁺ X⁺
X⁻ X⁺X⁻ X⁺X⁻
Y X⁺Y X⁺Y
F1) 4/4 = 100% of the progeny will express red eyes
50% of individuals are red-eyed males, X⁺Y
50% of individuals are red-eyed heterozygous females, X⁺X⁻
Option 2: true-breeding white-eyed females and red-eyed male
Parentals) X⁻ X⁻ x X⁺Y
Phenotypes) Red-eyed female White-eyed male
Gametes) X⁻ X⁻ X⁺ Y
Punnett square) X⁻ X⁻
X⁺ X⁺X⁻ X⁺X⁻
Y X⁻Y X⁻Y
F1) 2/4 = 50% of the progeny will be females expressing red eyes, X⁺X⁻
2/4 = 50% of the progeny will be white-eyed males, X⁻Y
