1.
- X^W X^W: red-eyed female (homozygous)
- X^W X^w: red-eyed female (heterozygous)
- X^w X^w: white-eyed female
- X^W Y: red-eyed male
- X^w Y: white-eyed male
2.
- White-eyed male: X^w Y
- Red-eyed female (heterozygous): X^W X^w
- White-eyed female: X^w X^w
- Red-eyed male: X^W Y
3.
Parental cross: X^W X^W × X^W Y
Offspring genotypes:
- Females: all X^W X^W
- Males: all X^W Y
All offspring have red eyes.
4.
Cross: pure red-eyed female (X^W X^W) × white-eyed male (X^w Y)
Offspring genotypes:
- Females: all X^W X^w (red-eyed)
- Males: all X^W Y (red-eyed)
All offspring have red eyes.
5.
Cross: red-eyed female (heterozygous) (X^W X^w) × red-eyed male (X^W Y)
Offspring genotypes:
- Females: 50% X^W X^W, 50% X^W X^w — all red-eyed
- Males: 50% X^W Y (red-eyed), 50% X^w Y (white-eyed)
Phenotypic ratio: 3 red-eyed : 1 white-eyed (all white-eyed are male)
Math: In the above cross, 100 males were produced and 250 females. How many non-red-eyed flies would there be?
Answer: 25 (only white-eyed males, which are 25% of 100 males)
Parent Tip: Review the logic above to help your child master the concept of genetics x linked genes worksheet.
