AP Biology
Investigation #7: Mitosis and Meiosis
Chi-Square Analysis on Treated Root Tips
Experiment:
 Scallions were treated as described in the AP Biology Laboratory Manual.

Treatment Groups:
o control (water)
o lectin (5 mg/100 ml) [L-2646 from Sigma; 25 mg costs ~$70; this is enough for
6-10 classes]
o 1, 5, 10, 100 mM caffeine (in water)

Scallion root tips grown for 48 hours in dark; they were fixed and stored in 70% ethanol
as described in the lab manual.
Results: (observed at 400 x)
 In the control roots (water), 86% of cells were in interphase; 14% in mitosis
Tip
Treatment
Interphase Prophase
Number of Cells
Metaphase Anaphase/Telophase Total
Control
460
43
8
24
535
Lectin
417
117
51
41
626
549
18
3
5
575
449
11
2
7
469
330
9
3
0
342
1 mM
caffeine
5 mM
caffeine
10 mM
caffeine
100 mM
caffeine
Cytotoxic
Nuclei appeared “blebby” with caffeine treatments, noted cells with vesicles.
Alternative treatment of tips
1. Heated in 1 M HCl at 60oC for 5 minutes
2. Rinsed with water, water removed with Kimwipe
3. Stained
4. Blotted up excess stain with Kimwipe
5. Added 1 drop of water
6. Used needles to gentle tease apart root
7. Squashed tip
Alternative dye:
 1 % toluidine blue in water
AP Biology
Investigation #7: Mitosis and Meiosis
Chi Square Test for Treated Alium (scallion) Roots


In the Control roots (water), 86% of cells were in interphase; 14% in mitosis
Calculate expected (e) number of cells by multiplying total by control percentage.
Lectin treatment
o
e
(o-e)
(o-e)2
(o-e)2
e
interphase
mitosis
Σ (o-e)2 = experimental χ2 =
e
Caffeine, 1 mM
o
e
(o-e)
(o-e)2
(o-e)2
e
interphase
mitosis
Σ (o-e)2 = experimental χ2 =
e
Caffeine, 5 mM
o
e
(o-e)
(o-e)2
(o-e)2
e
interphase
mitosis
Σ (o-e)2 = experimental χ2 =
e
Caffeine, 10 mM
o
e
(o-e)
(o-e)2
(o-e)2
e
interphase
mitosis
Σ (o-e)2 = experimental χ2 =
e
AP Biology
Investigation #7: Mitosis and Meiosis
Decision Rule:
 Reject the null hypothesis (treatment has no effect) if the experimental χ2 > table
χ2.
 Use the 5% probability (0.05) column.
http://passel.unl.edu/Image/Namuth-CovertDeana956176274/chi-sqaure%20distribution%20table.PNG