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biol139-lecture20-2011

# Are abab abab ab ab ab ab 2 18 1252 15 1252 125 125

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Unformatted text preview: 3 p value greater than 0.05 ∴accept null hypothesis that genes may not be linked Total number offspring = 50 Number of classes = 4 null hypothesis predicts 1:1:1:1 1:1:1:1 Number offspring expected in expected each class = 50 x .25 = 12.5 12.5 + (7-12.5)2 + (10-12.5)2 12.5 12.5 P 31 25 R 19 25 Instead of 1:1:1:1 ratio with 4 classes (from previous example) can simplify and combine into two classes: i.e. parentals:recombinants Observed values deviate from values predicted by our hypothesis, but is this significant? Degrees of freedom = # classes -1 =2-1 =1 for χ 2 = 2.88 and df = 1, table shows p is greater than 0.05 ~0.09 Therefore we accept the null hypothesis that the genes are not linked • • • p value high, likely hypothesis being tested is correct high deviation from expected is insignificant insignificant fail to reject hypothesis that genes are not linked genes • p value very low, observed deviation from expected very results becomes significant significant unlikely hypothesis being tested explains data hypothesis is rejected and genes may be linked may • • Recombination results when crossing-over during meiosis separates linked genes Reciprocal exchanges are the physical basis of recombination Proven through use of physical markers: cytologically visible abnormalities that make it possible to keep track of specific chromosome parts from one generation to the next 1931- Harriet Creighton and Barbara McClintock, studies Harriet studies with corn; Curt Stern, studies with Drosophila Curt studies Drosophila Stern demonstrated genetic recombination results genetic when crossing-over between chromosomes during when meiosis separates linked genes meiosis Stern’s Experiment in Drosophila Stern’s Drosophila Physical markers -abnormalities in chromosomes Bred females with 2 different X chromosomes • one was shorter -discontinuity • one had piece of Y chromosome attached Genetic markers - genes serving as points of reference to determine if progeny were result of recombination • carnation eyes (dark ruby colour) • kidney shaped (bar) Demonstration that genetic recombination depends on the reciprocal exchange of parts between maternal and paternal chromosome shorter part of Y attached...
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