Saturday, 15 September 2012

Deconvoluting a genetics question (branch diagram solution)

One of the common tasks for a genetics student is to break down a complex question and solve it systematically.  Here's the kind of question I often put on an exam.  There are several ways to solve it; I include one that uses a branch diagram to find the answer.

Wednesday, 12 September 2012

The theory behind the Chi2 test

Most textbooks do a pretty bad job in describing how the Chi2 test works and how to apply it.

Here's my first video on the subject.  It goes into the theory behind the Chiformula and when you would apply the statistic to your data.  The components of the Chi2 formula are discussed so you should be able to get an idea what it measures.  

The Chi2 test is commonly taught in Genetics courses to give students a tool to assess whether data could belong to particular ratios (e.g. 3:1, 1:2:1, 9:3:3:1). After viewing this video, you should:
  •  recognize that the Chi2 formula measures deviation of and observed value from a theoretical value for purposes of comparison
  • be able to calculate the Chi2 score from a set of data
  • determine the degrees of freedom for a particular sample 
  • be able to reject or fail to reject a set of data from a theoretical population by using the Chi2 table
Actually doing the Chi2  test is quite simple.  I'll provide a few examples of calculating the Chi2 value and interpreting it using the Chi table.