Mapping of X-linked yellow body, white eyes, and vermilion eyes loci.

Sturtevant's data

y we v / + + + X y we v /Y

we = "white-eosin"

Total Progeny

  

y we v

+ + +

197

215

Parentals

y we +

+ + v

105

98

recombinants

y + +

+ we v

4

3

recombinants

+ we +

y + v

1

0

double

recombinants
 

623

total flies

Determine relative order of the genes. Order is as shown.

Calculate map distances:

w - v interval = w- v recombinants / total = 105 + 98 + 1 = 204 /623 = 32.7%

y - w interval = 4 + 3 + 1 = 8 / 623 = 1.3 %

y - v interval = 105 + 98 + 4 + 3 + 2 (1) = 213 /623 = 34 %

So the map is: y --1.3cM--w--------------------32.7cM------------------v

Analyze double crossovers (DCO):

Expect (0.13) (.33) X 629 total = 2.7. So expected 3 but got only 1 double recombinant.

Coefficient of coincidence = # observed DCO / # expected DCO = 1/3

Interference = 1 - Coeff. of coinc. = 0.67 = 67 % interference.

Study questions:

1) Why was the we allele used here?

2) How would you have mapped these genes if you only had a w- null allele (no function)?

3) How could you determine map order if there was no double recombinant class?