This work was created by Dr Jamie Love and Creative Commons Licence licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Self Assessment Questions for Lesson 11

Chi Square

by Dr Jamie Love Creative Commons Licence 2002 - 2005

#1

Here's a Chi-square Table and the equation for the chi-square is 2 = [(O - E)2/E]

Plants true-breeding for green pods were crossed with plants true-breeding for yellow pods and all the F1s were green.
These F1s were allowed to self-fertilize and
152 of the F2s produced yellow pods while the remaining
428 F2s produced green pods.

Degrees of Freedom 5 % Significance Levels
1
3.84
2
5.99
3
7.81
4
9.49

Use the chi-square to determine if these results are within the range of the expected ratio.

Go to the ANSWER

#2

Here are the results of a dihybrid cross involving roses. There is no need to tell you their history other than to say they are the result of a proper dihybrid cross. The F2s produced had these phenotypes and in these numbers.
Red and tall = 30
White and tall = 65
Red and short = 83
White and short = 206
Use the chi-square to determine if these results are what you would expect for the dihybrid cross.
Note and warning! This will take you more time and effort than the other chi-square, in the first SAQ of this section, so take it one step at a time and be sure you remind yourself that there are now four categories. You might want to set this up as a neatly organized table to follow because it gets pretty complicated!
2 = [(O - E)2/E]

Degrees of Freedom 5 % Significance Levels
1
3.84
2
5.99
3
7.81
4
9.49

Go to the ANSWER

#3

A fish biologist collects 70 female trout and 50 male trout from a river down steam of a chemical plant. She suspects that the plant is releasing a chemical that changes the sex ratio in the river. (Maybe the plant releases chemicals that kill males more than females or maybe it is releasing chemicals that cause males to become females! )

Calculate the chi square and use it to determine if the sex ratio of this trout population is "off" (or "skewed" as statisticians say).
Hint : start by asking, "What would be the numbers of males and females if nothing was wrong?".

You'll need this table, on the right, to come to a conclusion.

Degrees of Freedom
5 % Significance Levels
1
3.84
2
5.99
3
7.81
4
9.49

Go to the ANSWER

#4

While conducting a survey of a large, extended family, a doctor observed 8 of the men and boys are colorblind and an equal number (8) men and boys are NOT colorblind. In this same family, he finds that only two of the women and girls are colorblind while the remaining 14 women and girls are not colorblind.

It seems the males are more likely to be colorblind. Is there a link between the sex of the person and whether she/he is colorblind?

We will use the chi-square, in the next question, to find out.

But first, tell me the expected numbers of normal and colorblind males and females if there is no link between sex and colorblindness.

That is, how many of each of these four groups should you expect if there is no link between sex and colorblindness?

Answer that question by completing this table.

Hint : ask yourself, "How many people in this population are colorblind and how would I distribute that number equally between the two sexes?".

Phenotypes
Expected
Normal males
Colorblind males
Normal females
Colorblind females
Total
32

Go to the ANSWER

#5

Use the information from the previous question to determine if there is something "strange" about the distribution of colorblindness between the sexes in this population.

Below is a summary of what you know so far.

Phenotypes
Observed
Expected
Normal males
8
1
Colorblind males
8
5
Normal females
14
11
Colorblind females
2
5
Total
32
32

And you will need this table.
Degrees of Freedom
5 % Significance Levels
1
3.84
2
5.99
3
7.81
4
9.49

Go to the ANSWER

This work was created by Dr Jamie Love and Creative Commons Licence licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.