How to Determine Chi Square Testing
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How to Determine Chi Square Testing

This articles is about chi square testing and what steps are used to determine the value of the chi square testing. Also, this article is about understanding degrees of freedom/probability values and how it relates back to chi square testing. This article gives readers a step by step approach in finding the chi-square value and the probability value using the chi-square value.
         Chi square testing is used in genetics to test for values that may or not be significant.  The formula for chi square testing is the summation of observed- expected squared divided by the expected. In order to use chi-square test, there needs to be data. The data will be the monohybrid and the dihybrid ratio. There are certain steps to take when doing chi square testing. The first step is to know how to draw punnet squares. Punnet squares are able to determine the gametes of the offspring.  Punnet squares test for the ratios of certain types of genotypes. The second step is to know how to determine the expected values. In order to determine the expected value, the probability of the punnet square will need to be known. Each probability of the punnet square will be used to multiply the total number of the observed values.  This value will be the expected value. Now plug in the values for observed and the expected values into the chi square testing formula and use the value to look up the probability value in the given critical values of chi square testing distribution.

         To find the probability value of the chi square testing, find the degrees of freedom. To test for degrees of freedom count the number of the gametes and subtract by one. In order for the chi square test to have a significant difference, the p value should be less than 0.05 %. In order for the chi square test to not have a significant value, the p value will have to be larger than 0.01%. A scenario could be red flowers and blue flowers. Blue flowers could represent bb and red flowers will represent RR. These two flowers will cross. The values that represent bb will be 105 for blue flowers and RR will be 45 for red flowers. These values are known as the observed values. To find the expected values of the two flowers, make a punnet square of bb and RR. The probability values of the punnet square will be 1/4 for bb, ½ for Rb, and ¼ for RR. These probability values will be used to multiply the total number of observed values which is 150.

         There should be two numbers calculated for the expected values which are 112.5 and 37.5. Now all the values are known to plug in the givens for the chi square testing equation. The degrees of freedom will be 1. The last thing to do to determine the probability value for the chi square testing is to look at the critical value table in the right degrees of freedom.  In the row of degrees of freedom, look for the total chi-square testing number. The probability value will be between two values. These steps and example shows and tells how to determine the chi-square testing.

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