X2 Tests Part I
X2 Test With More Than 1 df
X2 test is calculated without Yate's correction
term.
Di-hybrid F
cross AaBb results in four possible classes, assuming complete
dominance gene action at both loci.
| |
A_B_ |
A_bb |
aaB_ |
aabb |
Totals |
| observed |
1080 |
210 |
200 |
110 |
1600 |
| expected |
9
(1600)
16
=900
|
3
(1600)
16
=300 |
3
(1600)
16
=300 |
1
(1600)
16
=100 |
|
| observed-expected |
+180 |
-90 |
-100 |
+10 |
|
(observed-expected)
expected
|
36.00 |
27.00 |
33.33 |
1.0 |
|
X
= 36.00 + 27.00 +33.33 + 1.0 = 97.33
4 classes - 1df = 3df. If we know the total number of individuals,
then three classes are variable and the fourth class number
is fixed.
Critical X
with 3df, a = 0.05 = 7.82. The
calculated X
= 97.33 is larger than would be expected to occur in 95% of
repeated experiments, reject Ho.
