# VCU BIOL 310 - Chi Squares (4 pages)

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## Chi Squares

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## Chi Squares

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An introduction of Chi Squares

Lecture number:
4
Pages:
4
Type:
Lecture Note
School:
Virginia Commonwealth University
Course:
Biol 310 - Genetics
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BIOL 310 1st Edition Lecture 4 Outline of Previous Lecture Mendelism I A re examination of Mendel s Observations and Conclusions II Alternative method for Dihybrid Crosses III Mixed Crosses IV 4 trait mixed cross Outline of Current Lecture I II Testing agreement of hypotheses and data a Chi Squares b What is a P Value Mendels tests F2 s of round yellow X wrinkled green i A re examination of Mendel s Observations and Conclusions CHI SQUARE GOODNESS OF FIT TEST For example IF YOU FLIP A COIN 100 TIMES YOU EXPECT o 50 heads and 50 tails Do you really expect to see those results o No but expect something close to it Why not random chance deviation If flip 10 times versus 100 times does proportional deviation remain constant o No you get a 6 4 vs a 51 49 so as you increase the number of times you flip the coin the proportion gets closer Impact of absolute deviation decreases with larger sample size Many statistical tests attempt to determine whether observed deviation from theoretical expectation can be explained by random chance alone How 1 DEVELOP NULL HYPOTHESIS observed expected Or No real difference between expected and observed These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 2 USE STATISTICAL METHODS e g CHI SQUARE TEST t Test and many others a CHI SQUARE TEST Observed Expected 2 Expected for each all classes Value compared to table to interpret FOR EXAMPLE MENDEL S F2 FLOWER COLOR DATA Observed Expected Expected DEV Number Proportion Number O E 705 purple 697 8 O E 2 E 64 697 0 09 224 white 929 total 64 232 0 28 2 0 37 4 4 232 929 8 0 Expected Number total proportion DEV Observed Expected What is the null hypothesis o No real difference between E and O What is the working hypothesis o purple white 2 To assess the value take into account the number of degree s of freedom o Degrees of Freedom d f number of classes 1 o In this case d f 2 classes purple and white 1

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