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## CHI SQUARE

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**CHI SQUARE**X²**“MATHEMATICAL JUDGE” OF PROBABILITIES**• X² =∑{(O-E)²/E} • ∑= the sum of • O= observed E= expected**Chi square is used to measure the significance of the data**in comparison with what you expect to get.**Problem #1**• F2= 5,474 yellow seeds & 1850 green seeds • 1. Find the total # of seeds • 2. What is the expected ratio? • 3. How may yellow and green seeds would you expect? Yellow________,green____**4. For yellow seeds, used the formula**• (O-E)²/E. Yellow ________ • 5. For green seeds , use above formula. green _______ 6. Add the #’s together.**Did you get?**• 0.263 • Yea!!!!!!!!!!!!!!!!!**With one degree of freedom we could be allowed a chi square**as large as 3.84 and the results would still be considered significant to 5%. X² = 0.263 there’s less than a 5% chance this 3:1 happened by accident.**The degrees of freedom are one less than the number of**categories you have to work with. We have two categories, yellow and green, so we have one degree of freedom.**Find the chi square for the C-fern.**• Use the class totals. • The p= cc X Cc • cc= polka dot and is recessive • Cc = wild type and heterozygous • What would the expected ratio for F1 be with this cross?