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

Watch
Adorable98
Badges: 15
#1
Report Thread starter 4 years ago
#1
I know this is biology, but no one answered me in the biology forum, and cos the Chi square test is also part of Maths, I thought I might hopefully get some responses here.

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:

Image

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?
Attached files
0
reply
Alexion
Badges: 17
Rep:
?
#2
Report 4 years ago
#2
(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:
2
reply
Adorable98
Badges: 15
#3
Report Thread starter 4 years ago
#3
(Original post by Alexion)
X
Aha, now I get it, Thanks!!
0
reply
Zacken
Badges: 22
Rep:
?
#4
Report 4 years ago
#4
(Original post by Adorable98)
Aha, now I get it, Thanks!!
Can you see that when you do it via Alexion's way, the sum of your expected values sum to 100, as expected?
0
reply
Adorable98
Badges: 15
#5
Report Thread starter 4 years ago
#5
(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?
Yes, but should the sum always add up to a 100 ?
0
reply
Zacken
Badges: 22
Rep:
?
#6
Report 4 years ago
#6
(Original post by Adorable98)
Yes, but should the sum always add up to a 100 ?
No, it should always add up to whatever your observed things add up to.
1
reply
Adorable98
Badges: 15
#7
Report Thread starter 4 years ago
#7
(Original post by Zacken)
No, it should always add up to whatever your observed things add up to.
Oh, I see!! Thanks
0
reply
Zacken
Badges: 22
Rep:
?
#8
Report 4 years ago
#8
(Original post by Adorable98)
Oh, I see!! Thanks
No worries.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Current uni students - are you thinking of dropping out of university?

Yes, I'm seriously considering dropping out (150)
14.78%
I'm not sure (44)
4.33%
No, I'm going to stick it out for now (303)
29.85%
I have already dropped out (26)
2.56%
I'm not a current university student (492)
48.47%

Watched Threads

View All
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise