The Calculation of X
Mather, K. 1963. Measurement of Linkage in Heredity. John
Wiley and Sons, New York, pgs. 24-25.
The general formula is:
where a and mn are the observed and expected numbers in any
class.” “For a family segregating into two classes, whose
expected ratio is 
:1,
and the observed numbers are a1:a2
X2 = (a1 - a2
)
n
The special cases of this formula for the more usual genetical
expectations are:”
| Ratio |
Formula |
| 1:1 |
1(a1-a2)2
n |
| 3:1 |
1
(a1-3a2)2
3n |
| 15:1 |
1 (a1-15a2)2
15n |
| 1:3 |
1
(3a1-a2)2
3n |
| 9:7 |
7
(a1- (9/7)a2)2
9n |
