You are trying to map the linked recessive genes black body

You are trying to map the linked recessive genes black body (b) vestigial wing (vg), and cinnabar eye (cn) on chromosome 2 of Drosophila melanogaster. You cross wild-type females by triple mutant homozygoys males and obtain all wild-type F1. You then testcross the wild-type F1 females (what is the male genotype in this cross?) and collect the following data: Draw the genetic map of these genes as best you can, showing the gene order and distances (in centi Morgans) between genes.

Solution

Answer:

(F1 wild female)b+b vg+vg cn cn X (homozygous recessive male) bb vgvg cncn

Phenotypes

Short hand genotypes

Observed Number

Wild-type

b+ vg+ cn+

4150

Black, vestigial, cinnabar

b vg cn

4075

vestigial

b+ vg cn+

425

Cinnabar, black

b vg+ cn

450

Cinnabar, vestigial

b+ vg cn

381

black

b vg+ cn+

437

Cinnabar

b+ vg+ cn

50

Black, vestigial

b vg cn+

25

9993

Imaginary order is b+ vg+ cn+ / b vg cn

1.      If single cross over (SCO) occurs between b+ & vg+

Normal order= b+---------vg+ & b-----vg

After cross over= b+-----vg & b------vg+

b+-----vg recombinants are 425 + 381 = 806

b------vg+ recombinants are 450+ 437 = 887

Total recombinants = 1693

RF = (1693/9993)*100 =16.94%

2.      If single cross over (SCO) occurs between vg+ & cn+

Normal order= vg+---------cn+ & vg----cn

After cross over= vg+-----cn & vg------cn+

vg+-----cn recombinants are 450+50 = 500

vg------cn+ recombinants are 425+25 = 450

Total recombinants = 950

RF = (950/9993)*100 = 9.5%

3.      If single cross over (SCO) occurs between b+ & cn+

Normal order= b+---------cn+ & b------cn

After cross over= b+-----cn & b------cn+

b+-----cn recombinants are 381+ 50 = 431

b------cn+ recombinants are 437+ 25= 462

Total recombinants = 893

RF = (893/9993)*100 =8.94%

% RF = distance between the genes

The order of genes is -----

b+---8.94 cM---cn+----9.5 cM.----vg+

Phenotypes	Short hand genotypes	Observed Number
Wild-type	b+ vg+ cn+	4150
Black, vestigial, cinnabar	b vg cn	4075
vestigial	b+ vg cn+	425
Cinnabar, black	b vg+ cn	450
Cinnabar, vestigial	b+ vg cn	381
black	b vg+ cn+	437
Cinnabar	b+ vg+ cn	50
Black, vestigial	b vg cn+	25
		9993