# problem in predicting crossing result

Linyi Wang 1wang at rzdspc5.informatik.uni-hamburg.de
Wed Feb 2 09:58:55 EST 1994

```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
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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 method, the (perhaps mathematic)
probblem begins to disturb up 4 pairs.