Biology Unit1
18/03/25
Statistics & CHI Square test
Levels of Confidence
Confidence Limits (CL)
Confidence Intervals (CI) – expresses a range of values within which we are
pretty sure the population parameter lies.
Null Hypothesis – expresses against a prediction that there is no significant
difference between observed a predicted result
A hypothesis is a proposed explanation based on limited evidence (sample)
The CHI Square test ( 𝑋 2 = ∑
(𝑜−𝑒) 2
is used to determine whether any
𝑒
difference between two groups (observed and expected) are significant.
(O- observed, E-expected, ∑ - sum)
Mendelian Laws
 Law of Segregation
- States that when an individual produces gametes, the alleles separate so that
each gamete receives only one member of each pair eg- Aa Bb (parent)
AB, Ab, ab, Ab (possible gametes)
 Law of Independent Assortment
-States that alleles of different genes assort independently or randomly of one
another during the formation of gametes.
DOF – Degrees of Freedom (n -1) n= # of samples
Example using a Monohybrid chart
-
A farmer planted 180 seeds of peas. He observed that 129 of them had yellow
seeds and 45 of them had green seeds.
a) What would the expected phenotypes of the expected results
b) Through statistical analysis, establish or not if there is a significant difference
between the observed and expected data
n
Number observed
(‘O’)
Number
expected(‘E’)
Yellow
129
Green
51
135
45
Total
180
(O-E)
(𝑂 − 𝐸)2
(𝑂 − 𝐸)2
E
129- 135 = -6
36
36
= 0.27
135
6
36
0.8
Cal. – Step 1
-
Calculate ‘E’ based on phenotype ratio
Monohybrid yellow 3:1
3
4
× 180 = 135
green
1
4
× 180 =
Step 2
-
Step 3
-
Calculate the
∑ = 1.07