Chi-Squared Test & Epistasis (5.1.2)

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What does the chi-squared test do?
It allows us to calculate the probability of observing any departure from the expected ratio.
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What is always the null hypothesis?
There is no difference between the observed and expected results.
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What is the chi-squared formula?
The sum of: (observed-expected) squared, divided by expected.
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How do you work out the degrees of freedom?
N-1. With N being the number of different outcomes.
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What do you look up in the chi-squared table?
Degrees of freedom, against 5% probability level.
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What does it mean if your value is smaller than the critical value?
This means there is a less than 5% probability that there is a significant difference between the observed and expected results, so we accept the null hypothesis.
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What is epistasis?
Where the alleles present for one gene affect the expression of another gene.
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What is recessive epistasis?
If the first allele is homozygous recessive, it stops the expression of the second allele.
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What is dominant epistasis?
The presence of a dominant allele at the first gene locus masks the expression of alleles at the second gene locus.
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What are the two ways epistasis can work?
Antagonistically or in a complementary fashion.
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What does working in a complementary fashion mean?
Sometimes the first gene can code for an intermediate compound, and the second gene codes for an enzyme needed to convert the intermediate into a final product.
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Why does epistasis reduce variation?
Certain allele combinations for one gene can only be expressed if certain allele combinations for another gene are present. Sometimes the alleles of one gene are hidden and won't show up in the phenotype.
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Card 2

Front

What is always the null hypothesis?

Back

There is no difference between the observed and expected results.

Card 3

Front

What is the chi-squared formula?

Back

Preview of the front of card 3

Card 4

Front

How do you work out the degrees of freedom?

Back

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Card 5

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What do you look up in the chi-squared table?

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