1 / 8

Will use Fruit Flies for our example

Will use Fruit Flies for our example. R = Red eyes Rr X Rr r = White eyes. The Chi-Square Test. Used to confirm whether a set of data follows a specific probability distribution. IE…how likely is it that deviations from expected results are due solely to chance?.

andreaj
Download Presentation

Will use Fruit Flies for our example

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Will use Fruit Flies for our example • R = Red eyes Rr X Rr • r = White eyes

  2. The Chi-Square Test Used to confirm whether a set of data follows a specific probability distribution. IE…how likely is it that deviations from expected results are due solely to chance?

  3. Goodness-of-fit test • Uses a sample to test whether a frequency distribution fits the predicted distribution • Example: Used to answer the following ques • Can we conclude that the 3:1 ratio is true based on the observation of _____(#) of fruit flies.

  4. Observed vs. Expected Frequencies • The chi-square test basically compares the observed (O) and the expected (E) frequencies to determine whether there is a statistically significant difference • Observed frequency is the # of flies seen for each phenotype • Expected frequency is the # of flies expected for each penotype • Example: if cross is a monohybrid one, you would expect a 3:1 phenotypic ratio. Therefore, if you observed 100 flies, 75 of them should have the dominant phenotype, while 25 of them should have the recessive phenotype

  5. Chi-square statistic • Use the following equation:

  6. Determining the Critical Chi-Square Score • Use an already constructed table to see where your Chi-square value falls. • Which row you look in depends on the number of degrees of freedom. • The number of degrees of freedom is equal to the number of phenotypic categories minus 1. • Monohybrid… • Dihybrid… • Sex-linked…

  7. Chi-square Values and Probabilities • 2 ways to analyze • if X2 is less than number in box, good fit… • If P value is greater than .05, than good fit Means your data did not happen by chance.

  8. Let’s do an example problem • A cross between two fruit flies that are heterozygous for red eyes produced the following offspring: • 260 Red eyes • 178 White eyes • Calculate X2 for this experiment

More Related