You are working with two recessive mutations in Drosophila: e causes ebony and ro causes rough eyes. You cross a true-breeding strain of ebony flies (e e, ) with a true-breeding strain of rough-eyed flies ( , ro ro). You then cross the F1 to a true-breeding strain with ebony body and rough eyes. a) What are the predicted F2 genotype proportions if e and ro are on separate chromosomes

Question

06-03-2020
Biology

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You are working with two recessive mutations in Drosophila: e causes ebony and ro causes rough eyes. You cross a true-breeding strain of ebony flies (e e, ) with a true-breeding strain of rough-eyed flies ( , ro ro). You then cross the F1 to a true-breeding strain with ebony body and rough eyes. a) What are the predicted F2 genotype proportions if e and ro are on separate chromosomes

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marianaegarciaperedo marianaegarciaperedo · Answer 1 · 2020-03-08T06:46:04+01:00

Answer:

The predicted F2 genotype proportions are 1:1:1:1

Explanation:

Available data:

e causes ebony

ro causes rough eyes

e and ro are recessive mutations

A- Cross a true-breeding strain of ebony flies (e e, ++) with a true-breeding strain of rough-eyed flies (++, ro ro)

Parental) e e , + + x + + , ro ro

Gametes) e+ e+ e+ e+ +ro +ro +ro +ro

Punnet square) e+ e+ e+ e+

+ro +e+ro +e+ro +e+ro +e+ro

F1) 100% +e+ro

B- Cross the F1 to a true-breeding strain with ebony body and rough eyes.

Parental) +e,+ro x ee, roro

Gametes) ++ ro+ e+ ero ero ero ero ero

Punnet square) ++ +ro e+ ero

ero +e+ro +eroro ee+ro eeroro

F2) 4/16=1/4 +e,+ro

4/16=1/4 +e,roro

4/16=1/4 ee,+ro

4/16=1/4 ee,roro

The predicted F2 genotype proportions are 1:1:1:1

You can also calculate it by making the punnet square for each gene and then multipling the genotypic proportions, like this:

Parental) e + x e e + ro x ro ro

Gametes) e + e e + ro ro ro

Punnet Squares) e + ro +

e ee +e ro roro +ro

F1) 1/2 ee F1) 1/2 +ro

1/2 +e 1/2 roro

F2 genotype proportions)

+e,+ro = 1/2 +e x 1/2 +ro= 1/4 +e,+ro

+e,roro= 1/2 +e x 1/2 roro= 1/4 +e,roro

ee,+ro= 1/2 ee x 1/2 +ro= 1/4 ee,+ro

ee,roro= 1/2 ee x 1/2 roro= 1/4 ee,roro