dihybrid cross ... are they linked?

9:3:4 due to epistasis.

yeehaw!  Muchas Gracias!

If genes are epistatic, this is a kind of linkage right?  The ratio obtained was 37:10:3:1, and this is similar to the 12:3:1 ratio?

I made a linkage map please check this for me and see if I'm right.


F2 progeny is
    
637 +; +
175 +; se
63 ap; +
17 ap; se
 
Recombinants between wild and sepia are 175
Recombinants between sepia and apterous are 17
Recombinants between wild and apterous are 63
Total progeny are 892
 
Frequency of recombination between wild and sepia are 175/892 = 0.196
Frequency of recombination between sepia and apterous is 17 / 892 = 0.323
Frequency of recombination between wild and apterous is 63 / 892 = 0.070
 
The genes are linked and the distance between the genes is
 
Sepia-----------------wild--------apterous
ß------0.196------àß---0.070----à
ß----------------0.323----------------à
 
Overall F2 ratio observed:
37 wild type: 10 wild and sepia: 3 wild and apterous: 1 apterous and sepia
According to chisquare analysis the ratio doesn’t fit the 9:3:3:1 ratio.

Hey confused_student, I downloaded an excellent example for you from one of our paid database. It will describe how it's done. Tell me if it is any help to you! The explanation is on page 1, example is on page 2.

Thanks bio man!  I'll try to download it but I'm on a dial-up connection, so I may have to wait until tomorrow. 
I'm mainly wondering if it is possible to DO a linkage map for epistatic genes.  Of course, I don't know for sure that these genes are epistatic.  These are my lab results, it's not from the text book.  I realize I posted in the wrong spot.
If a map can be made, I'm reasonably sure I made a good map. 

this is all wrong.  I'm freaking out.  please, someone help me!

Don't freak out confused_student.

Clearly then if the chi-square analysis doesn't fit the 9:3:3:1 ratio, then it is epistasis like lewis suggested.

Try to download that file I uploaded, it's really small so I wouldn't really effect anything. The document states:

A common observation in genetics is that the product of several different genes can interact to produce certain phenotypes. Two independent genes (e.g. non-interacting), each with a dominant/recessive pair of alleles, will produce four phenotypes in a 9:3:3:1 ratio in the F2 generation of a dihybrid cross. However, if there is an interaction between the two genes (epistasis) a modified F2 dihybrid ratio may be observed.

A modified F2 dihybrid ratio of 9:3:4 is indicative of recessive epistasis.

Okay, I see the 9:3:4 listed as one of the common epistatic ratios.  But in this lab we got 37:10:3:1.  The lab TA cooked the books so that we would come to a conclusion. There is another epistasis ratio 12:3:1, and that's similiar to the last three numbers that the TA gave us.

My hair is on fire!!!!  If it is epistasis, should I try to map it? 

You're left with no other choice. Yes.