biol139-lecture20-2011

9 area 09 calculate the interference in this region

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Unformatted text preview: ient of coincidence = 1.2 = 0.75 Coefficient Interference = 1- 0.75 = 0.25 (interference but low!) Interference Interference Interference p j r 30.8 m.u. 10.0 m.u. 20.8 m.u. Computed an RF of 20.8 mu between p and j and an RF of 10.0 mu between j and r If crossing over is independent between region 1 and region 2, then the probability of a double cross over between these two regions is equal to the product of the probabilities of the two events occurring separately. 0.208 x 0.100 = 0.0208 We would expect 0.0208 double crossovers to occur However, if look at data set we only had an observed 6/500 flies or 1.2 % where a double cross over occurred. So the coefficient of coincidence is = observed DCO frequency/ expected DCO frequency = 0.012 / 0.0208 = 0.577 - means that only 57.7% of the expected DCO occurred Interference along this piece of DNA is 1 – 0.577 = 0.423 Testing Goodness-of-Fit to a Genetic Hypothesis: The Chi Square Test Hypothesis Testing: General Geneticists want to know if data they observe from a observe genetic cross is in satisfactory agreement with a theoretical or expected prediction (based on a hypothesis). expected Always bound to be statistical variation in observed results from variation experiment to experiment from that of expected! Devised test which decides whether an observed result deviates Devised observed too far from an expected result too expected Called Goodness of Fit -fit means how closely observed results Goodness “fit” with or agree with expected results For example: test cross F1 dihybrid pea (YyRr) with For homozygous recessive (yyrr) (YyRr x yyrr) Observed Results: Observed 568 progeny with 154 Y_R_:144 Y_rr:124 yyR_:146 yyrr 154 Hypothesis: 2 gene pairs assorting independently predicts an F2 ratio of 1:1:1:1 for 4 phenotypes predicts In theory expected values would be 142:142:142:142 142:142:142:142 Observed values deviate from values predicted by our hypothesis, but is this significant (reflecting a real difference between observation + theory) or insignificant (reflecting random insignificant sampling error or chance)? Question: if proposed genetic mechanism is correct, Question: what is probability of obtaining results that differ by this much or more from...
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