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Please help!! How do I CALCULATE the expected value? Chi square test!!

I know this is biology, but no one answered me in the biology forum:frown:, and cos the Chi square test is also part of Maths, I thought I might hopefully get some responses here.:biggrin:

An experiment was carried out to investigate the inheritance of grain shapes and colour in maize. The number of each type of grain on a cob were counted (observed number).
The results are shown in the table below:



it was predicted that the phenotype would be in the ratio 9 : 3 : 3: 1 and a chi-squared test was used to investigate whether there was a significant difference between the observed results and the expected results.

Complete the table by calculating the expected number (E) of grains of each phenotype.


--

So what I did was:
the ratio is 9 : 3 : 3 : 1

For yellow & smooth: 9/16 x 53 = 29.8125
Yellow & wrinkled: 3/16 x 20 = 3.75
and so on ...

but my answers are all wrong?? Where did I go wrong and what's the correct way to calculate the expected value?:frown:
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Reply 1
Avatar for Alexion
Alexion
17
Original post by Adorable98
^


You've got the right sort of idea.

But you want to multiply the expected ratio (i.e. 9/16) by the TOTAL count (53 + 20 + 17 + 10 = 100)

So they should be:

yellow/smooth: 9/16 * 100 = 56.25
yellow/wrinkled: 3/16 * 100 = 18.75
white/smooth: 3/16 * 100 = 18.75
white/wrinkled: 1/16 * 100 = 6.25

You can see that these are much closer to the observed values.

I'm sure you can fill out the last column yourself from that :cute:
Reply 2
Avatar for Adorable98
Adorable98
OP
15
Original post by Alexion
X


Aha, now I get it, Thanks!!:smile:
Reply 3
Avatar for Zacken
Zacken
22
Original post by Adorable98
Aha, now I get it, Thanks!!:smile:


Can you see that when you do it via Alexion's way, the sum of your expected values sum to 100, as expected? :biggrin:
Reply 4
Avatar for Adorable98
Adorable98
OP
15
Original post by Zacken
Can you see that when you do it via Alexion's way, the sum of your expected values sum to 100, as expected? :biggrin:


Yes:h:, but should the sum always add up to a 100 ?
Reply 5
Avatar for Zacken
Zacken
22
Original post by Adorable98
Yes:h:, but should the sum always add up to a 100 ?


No, it should always add up to whatever your observed things add up to.
Reply 6
Avatar for Adorable98
Adorable98
OP
15
Original post by Zacken
No, it should always add up to whatever your observed things add up to.


Oh, I see!! Thanks:h:
Reply 7
Avatar for Zacken
Zacken
22
Original post by Adorable98
Oh, I see!! Thanks:h:


No worries. :smile:

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