Problem in predicting crossing result

[Linyi Wang]

Hello people in net,
	I am an undergraduate biology student. I have some difficulty
in predicting the result of a D. melanogaster cross-test between male
wild type and female hybrid y cv v f /+ + + +. Theoretically, there
should be 2 high 4 equal 16 possible Genotypes under the sons. To
calculate their frequency, I need 16 equations. What a pity, I can
only find 15 equations at all: 

a. The sum of all 16 parts is 100%. (1 equation) 

b. Because of the reciprocal character of normal cross-over, 8 parts
are numerically equal to their corresponding 8 parts, for example the
frequency of y cv v + /- - - - ist equal the frequency of + + + f/- -
- - , ... (8 equations)

c. calculation of recombination between two allel pairs from four pairs
   (2)
   (4)=4x3/2=6 equations
-------------------------------------------------- 

you see that there are only 15 equations here.  There is no problem in
prediction in case of 2 or 3 allel pairs using the same methode, the (perhaps mathematic)
probblem begins to disturb up 4 pairs. 

Thanks in advance

Linyi Wang
e-mail: 1wang at rzdspc5.informatik.uni-hamburg.de