Question

in fruit flies eye color is a sex-linked trait where red eyes are dominant to the white eye phenotype. cross a male with red eyes with a purebred white eye female. use
\ for red and
\ for white.
mom→
dad↓
phenotypic ratio:
answer

Explanation:

Step1: Define parental genotypes

For sex-linked traits (X-linked in fruit flies):

• Red-eyed male: $X^R Y$ (males have one X and one Y chromosome)
• Purebred white-eyed female: $X^r X^r$ (homozygous recessive, since white is recessive)

Step2: Identify gametes produced

• Male gametes: $X^R$, $Y$
• Female gametes: $X^r$, $X^r$

Step3: Complete Punnett Square

	$X^r$	$X^r$
$Y$	$X^r Y$	$X^r Y$

Step4: Determine phenotypes

• $X^R X^r$: Red-eyed females (dominant R is expressed)
• $X^r Y$: White-eyed males (only recessive r on X)

Step5: Calculate phenotypic ratio

Count offspring phenotypes: 2 red-eyed females, 2 white-eyed males. Simplify the ratio.

Answer:

Punnett Square Fill-ins (top to bottom, left to right):

1. $X^R X^r$ (red-eyed female)
2. $X^R X^r$ (red-eyed female)
3. $X^r Y$ (white-eyed male)
4. $X^r Y$ (white-eyed male)

Phenotypic Ratio:

1 Red-eyed Female : 1 White-eyed Male