In drosophila melanogaster, black body (b) is recessive to normal color (b), pur

ID: 163061 • Letter: I

Question

In drosophila melanogaster, black body (b) is recessive to normal color (b), purple eyes (pr) are recessive to red eyes (pr^+), and vestigial wings (vg) is recessive to normal wings (vg^-). A female fly with a black body, purple eyes and vestigial wings is crossed to a wild type male. The F1 females produced by this cross were mated with black, purple and vestigial males in a testcross. The progeny resulting from the testcross are listed below. Determine order of these genes on the chromosome. Calculate the map distances between the genes. Determine the coefficient of coincidence and the interference among these genes.

Explanation / Answer

Answer:

Explanation

genotypes

Number of progeny

vg b pr

631

vg+ b pr

vg+ b+ pr

120

vg+ b+ pr+

640

vg+ b pr+

vg b pr+

125

vg b+ pr

vg b+ pr+

Total

1587

Parental combinations are more so, the parental combinations vg+ b+ pr+ & vg b pr

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

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

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

vg+ ----- b recombinants are 8+25= 33

vg------ b+recombinants are 10+28=38

Total recombinants = 71

RF = (71/1587)*100 =4.47%

2. If single cross over (SCO) occurs between b+ & pr+

Normal order= b+ --------- pr+ & b --------- pr

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

b+ --------- pr recombinants are 120+28=148

b ------ pr+recombinants are 125+25=150

Total recombinants = 298

RF = (298/1587)*100 = 18.78%

3. If single cross over (SCO) occurs between vg+ & pr+

Normal order= vg+ --------- pr+ & vg ----- pr

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

vg+ ----- pr recombinants are 8+120= 128

vg------ pr+recombinants are 10+125=135

Total recombinants = 263

RF = (263/1587)*100 = 16.57%

% RF = Map unit distance

The order of gene is -----

b ------4.47 m.u.------- vg -----------16.57 m.u.----------pr

Expected double cross over frequency (EDCO) = (RF between b/vg) * (RF between vg/pr)

= 0.0447 * 0.1657= 0.0074

Observed double cross over frequency (ODCO)= (8+10)/1587 =0.0113

Coefficient of Coincidence (coc)= ODCO/EDCO = 0.0113/0.0074=1.53

Interference= 1-coc= 1-1.53= -0.53