Question

fruit fly eye color
in fruit flies, eye color is a sex linked trait. red is dominant to white.

1. what are the sexes and eye color of flies with the following genotypes?

$x^rLXB0x^r$ $x^r

$$x^r$ $x^r$$

y$ $x^r$$y$

1. what are the genotypes of these flies?

white-eyed male __________ red-eyed female, heterozygous __________
white-eyed female __________ red-eyed male __________

1. show the cross of a white-eyed female and a red-eyed male and determine probabilities.

punnett square:
probabilities:
white-eyed male ____________
white-eyed female ____________
red-eyed male ____________
red-eyed female ____________

1. show the cross between a purebred red-eyed female and a white-eyed male and determine probabilities.

parent genotypes: __________ & __________
probabilities:
punnett square:
white-eyed male ____________
white-eyed female ____________
red-eyed male ____________
red-eyed female ____________

1. show the cross between a heterozygous red-eyed female and a red-eyed male and determine probabilities.

parent genotypes: __________ & __________
probabilities:
punnett square:
white-eyed male ____________
white-eyed female ____________
red-eyed male ____________
red-eyed female ____________
what if the above cross produced 100 males and 200 females. how many total red-eyed flies would you predict? (show your work.)

Explanation:

Step1: Solve Question 1

• $X^R X^r$: Female, red-eyed (carrier)
• $X^R X^R$: Female, red-eyed
• $X^r X^r$: Female, white-eyed
• $X^R Y$: Male, red-eyed
• $X^r Y$: Male, white-eyed

Step2: Solve Question 2

• White-eyed male: $X^r Y$
• Red-eyed female, heterozygous: $X^R X^r$
• White-eyed female: $X^r X^r$
• Red-eyed male: $X^R Y$

Step3: Solve Question 3

Step3.1: Define parent genotypes

White-eyed female: $X^r X^r$; Red-eyed male: $X^R Y$

Step3.2: Build Punnett square

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

Step3.3: Calculate probabilities

White-eyed male: $\frac{2}{4} = 50\%$
White-eyed female: $\frac{0}{4} = 0\%$
Red-eyed male: $\frac{0}{4} = 0\%$
Red-eyed female: $\frac{2}{4} = 50\%$

Step4: Solve Question 4

Step4.1: Identify parent genotypes

Purebred red-eyed female: $X^R X^R$; White-eyed male: $X^r Y$

Step4.2: Build Punnett square

	$X^R$	$X^R$
$Y$	$X^R Y$	$X^R Y$

Step4.3: Calculate probabilities

White-eyed male: $\frac{0}{4} = 0\%$
White-eyed female: $\frac{0}{4} = 0\%$
Red-eyed male: $\frac{2}{4} = 50\%$
Red-eyed female: $\frac{2}{4} = 50\%$

Step5: Solve Question 5

Step5.1: Identify parent genotypes

Heterozygous red-eyed female: $X^R X^r$; Red-eyed male: $X^R Y$

Step5.2: Build Punnett square

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

Step5.3: Calculate probabilities

White-eyed male: $\frac{1}{4} = 25\%$
White-eyed female: $\frac{0}{4} = 0\%$
Red-eyed male: $\frac{1}{4} = 25\%$
Red-eyed female: $\frac{2}{4} = 50\%$

Step5.4: Calculate total red-eyed flies

Red-eyed males: $100 \times 75\% = 75$
Red-eyed females: $200 \times 100\% = 200$
Total red-eyed flies: $75 + 200 = 275$

Answer:

1.

• $X^R X^r$: Female, red-eyed (carrier)
• $X^R X^R$: Female, red-eyed
• $X^r X^r$: Female, white-eyed
• $X^R Y$: Male, red-eyed
• $X^r Y$: Male, white-eyed

2.

• White-eyed male: $X^r Y$
• Red-eyed female, heterozygous: $X^R X^r$
• White-eyed female: $X^r X^r$
• Red-eyed male: $X^R Y$

3.
Punnett square:

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

Probabilities:

• White-eyed male: 50%
• White-eyed female: 0%
• Red-eyed male: 0%
• Red-eyed female: 50%

4.
Parent genotypes: $X^R X^R$ & $X^r Y$
Punnett square:

	$X^R$	$X^R$
$Y$	$X^R Y$	$X^R Y$

Probabilities:

• White-eyed male: 0%
• White-eyed female: 0%
• Red-eyed male: 50%
• Red-eyed female: 50%

5.
Parent genotypes: $X^R X^r$ & $X^R Y$
Punnett square:

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

Probabilities:

• White-eyed male: 25%
• White-eyed female: 0%
• Red-eyed male: 25%
• Red-eyed female: 50%

Total red-eyed flies: 275