The genes for ruby eyes (rb), tan body (t) and cut wings (ct) are all found on t

Question

The genes for ruby eyes (rb), tan body (t) and cut wings (ct) are all found on the X-chromosome of Drosophila melanogaster. All of these are recessive traits. They map in the order rb, ct, t with 15.5 map units between rb and ct and 5.5 map units between ct and t. Suppose you cross a cut wing male with a homozygous female that is both tan and has ruby eyes.

1) What will the F1 females look like? (Explain in detail)

2) Draw map of the section of the X chromosomes that has these 3 genes for the F1 females

3) Assuming you testcross your F1 females. What progeny classes would you expect?

Please explain answer in detail, I do not seek answer only but explanation to learn from. Same queston was posted but someone solved it with the traits being all recessive, so answer was incorrect.

Explanation / Answer

Genotype of female: XrbXrbXtXt XCTXCT

Genotype of male: XRBXT XctY

1.

Gametes of female: XrbXtXCT (total eight)

Gametes of male: XRBXT Xct and Y

Genotype of F1 females: XrbXtXCTXRBXTXct

Phenotype of F1 females: ( wild type)

2)

Xrb--------10.0mU-----------Xt----5.5mU----XCT      (1 homologous X chromosome from female)

            XRB--------10.0mU----------XT----5.5Mu----Xct     (2 homologous X chromosome from male)

3)

Genotype of F1 females: XrbXRBXt XTXCTXct

Genotype of Male for test cross: XrbXt XctY

XrbXt Xct

                Y

XrbXt XCT

XrbXt XCT XrbXt Xct

XrbXt XCT Y

XrbXt Xct

XrbXt Xct XrbXt Xct

XrbXt Xct Y

XrbXTXCT

XrbXTXCT XrbXt Xct

XrbXTXCT Y

XrbXTXct

XrbXTXct XrbXt Xct

XrbXTXct Y

XRBXt XCT

XRBXt XCT XrbXt Xct

XRBXt XCT Y

XRBXt Xct

XRBXt Xct XrbXt Xct

XRBXt Xct Y

XRBXTXCT

XRBXTXCT XrbXt Xct

XRBXTXCT Y

XRBXTXct

XRBXTXct XrbXt Xct

XRBXTXct

   

Females: Ruby, tan (1 / 16)                        

                 Ruby, tan, cut wings (1 / 16)

                 Ruby (1 / 16)

                 Ruby, cut wing (1 / 16)

                 Tan (1 / 16)

                 Tan, cut wing (1 / 16)

                 Wild type (1 / 16)

                 Cut wing (1 / 16)

Males: Ruby, tan (1 / 16)

            Ruby, tan, cut wing (1 / 16)

            Ruby (1 / 16)

            Ruby, cut wing (1 / 16)

            Tan (1 / 16)

            Tan, cut wing (1 / 16)

            Wild type (1 / 16)

            Cut wing (1 / 16)

XrbXt Xct

                Y

XrbXt XCT

XrbXt XCT XrbXt Xct

XrbXt XCT Y

XrbXt Xct

XrbXt Xct XrbXt Xct

XrbXt Xct Y

XrbXTXCT

XrbXTXCT XrbXt Xct

XrbXTXCT Y

XrbXTXct

XrbXTXct XrbXt Xct

XrbXTXct Y

XRBXt XCT

XRBXt XCT XrbXt Xct

XRBXt XCT Y

XRBXt Xct

XRBXt Xct XrbXt Xct

XRBXt Xct Y

XRBXTXCT

XRBXTXCT XrbXt Xct

XRBXTXCT Y

XRBXTXct

XRBXTXct XrbXt Xct

XRBXTXct

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