11. An evolutionary biologist examined the relative fitness for 2000 generations
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Question
11. An evolutionary biologist examined the relative fitness for 2000 generations (about 300 days) of E. coli bacteria at stressful acidic pH 5.5 and their parental generations grown and preserved at pH 7.2. Both types were later grown together in an acidic medium and their relative fitness was computed. The experiment was replicated for 6 different lines of E. coli giving the following data on relative fitness: A relative fitness of 1 means both bacteria types are equally fit and a value larger than 1 indicates that acid evolved line is more fit than the parental line. Do data provide evidence that bacteria evolved in acidic pH are better adapted to acidic conditions? You may use the level of significance as 10%. Also, (to reduce your computational burden) you may assume that sample mean and sample standard deviations are respectively, 1.2 and 0.0583.Explanation / Answer
This is a small sample of 6 E.coli lines, so, Student's t-test can be performed.
Null hypothesis is: - Bacteria evolved in acidic pH are better adapted to acidic environment.
Now null hypothesis will be accepted if calculated value is less than tabulated value.
When both the parental line and acidic line are mixed, and then grown in acidic pH, mean relative fitness comes out to be 1.2. Standard deviation is 0.0583 =s
sample size = n = 6
degree of freedom = n-1= 5
level of significance = 10%=0.1
SEM, (standard error of mean) = s/ n^1/2 = 0.0583 / 6^1/2 =0.024
t- value = mean/ SEM = 1.2/0.024= 50 . This is calculated value of F.
Tabulated value of t from t- table = 1.476
Here, calculated value is greater than tabulated value, so, null hypothesis should be rejected.
So, we can say that bacteria evolved in acidic pH are not better adapted to acidic environment.
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