Question

EXTRA CREDIT (10 pts) 7) In Drosophila, white eye is an X-linked recessive trait and ebony body is an autosomal recessive trait. A homozygous white-eyed female (normal body) is crossed with a homozygous ebony male (normal, red eyes). a) What phenotypic ratio do you expect in the F1 generation? Show your work. b) What phenotypic ratio do you expect in the F2 generation? Show your work.

Answer 1

Representation:

1.Trait of eye color: X-linked = W/w

• Wild type red- eyed male= X^WY
• White-eyed male = X^wY
• Wild type red-eyed female= X^W X^W/ X^W X^w
• White-eyed female = X^wX^w

2.Body type= Autosomal = E/e

• Wild type = EE/Ee
• Ebony = ee

Cross: White-eyed female x ebony bodied male

EE X^wX^w x ee X^WY

	Female
Male	EXw	E Xw	F1
eXW	Ee XWXw	Ee XWXw	Female
eY	EeXwY	EeXwY	Male

F1:

Ee X^WX^w = Wildtype bodied- Wildtype eyed female

EeX^wY = Wildtype bodied- white eyed male

Wildtype bodied- Wildtype eyed female: Wildtype bodied- white eyed male =1:1

F2:

Ee X^WX^w x EeX^wY

	EXW	EXw	eXW	eXw
EXW	EEXW XW	EEXW Xw	EeXW Xw	EeXw Xw
eXW	EeXW Xw	EeXw Xw	eeXW Xw	eeXw Xw
EY	EEXWY	EEXw Y	EeXWY	EeXw Y
eY	EeXWY	EeXw Y	eeXWY	eeXw Y

Wildtype bodied- Wildtype eyed female: 4

EEX^W X^W =1

EEX^W X^w = 1

EeX^W X^w =2

Wildtype bodied- White eyed female: 2

EeX^w X^w

Ebony bodied- Wildtype eyed female: 1

eeX^W X^w

Ebony bodied- Wildtype eyed female: 1

eeX^w X^w

Wildtype bodied- Wildtype eyed male: 3

EEX^WY =1

EeX^WY =2

Wildtype bodied- White eyed male: 3

EEX^w Y =1

EeX^w Y =2

Ebony bodied- Wildtype eyed male: 1

eeX^WY

Ebony bodied- Wildtype eyed male: 1

eeX^w Y

Ratio: 4:2:1::1:3:3:1:1