13. Two different female Drosophila were isolated, each heterozy- gous for the a

Question

13. Two different female Drosophila were isolated, each heterozy- gous for the autosomally linked genes b (black body), d (dachs tarsus), and c(curved wings). These genes are in the order with b being closer to d than to c. Shown here is the genotypic arrangement for each female along with the various gamete formed by both er d-b-c, Female A d b + Female B Gamete formation (1) d b c (5) d +) db(5) d b c c(7) d+ c (3) d+ c (7) d + + (4) d b (8)+b (4)+ b+ (8) b C Identify which categories are noncrossovers (NCOs), single crossovers (SCOs), and double crossovers (DCOs) in each case. Then, indicate the relative frequency in which each will be produced

Explanation / Answer

Female A

Single cross over (SCO) 1. d b c , 2. + + +, 7. d + c, 8. + b +

Non cross over (NCO) 3. + + c, 4. d b +

Double cross over (DCO) 5. d + + , 6. + b c

Female B

Single cross over (SCO) 3. d + c, 4.+ b +, 5. d b c, 6. + + +,

Non cross over (NCO) 7. d + +, 8. + b c

Double cross over (DCO) 1. d b + , 2. + + c

Relative frequency

d is very close to b so the relative frequency is very low compared to d and c.

Female A

Non cross over (NCO) 3. + + c, 4. d b + = Relative frequency is 0

Single cross over (SCO)   7. d + c, 8. + b + = Relative frequency is low

Single cross over (SCO) 1. d b c , 2. + + +,= Relative frequency is high

Double cross over (DCO) 5. d + + , 6. + b c = Relative frequency is very very low.

Female B

Non cross over (NCO) 7. d + +, 8. + b c = Relative frequency is 0

Single cross over (SCO) 5. d b c, 6. + + +, = Relative frequency is low

Single cross over (SCO) 3. d + c, 4.+ b +,= Relative frequency is high

Double cross over (DCO) 1. d b + , 2. + + c = Relative frequency is very very low.

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