Because sometimes a crossover in one region of the

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Unformatted text preview: gion of the chromosome will reduce the likelihood of a crossover in an adjacent part of the chromosome i.e., if the recombination frequency in region I is 15% and 5% in region II, we would expect the frequency of double crossovers for regions I and II together to be (0.15)(0.05) = 0.0075 = 0.75% A smaller value would indicate interference. 28 Interference Will occur when examining 3 genes that are relatively close together -difficult to get double-cross over events 29 Interference It is not uniform, and may vary for different regions of the chromosome A quantitative measure of the amount of interference in a particular chromosomal region is first obtained by calculating the coefficient of coincidence Coefficient of coincidence = Frequency observed Frequency expected Interference = 1- coefficient of coincidence 30 Interference Coefficient of coincidence = Frequency observed Frequency expected Interference = 1- coefficient of coincidence If there is no interference (interference = 0), then the observed frequency of double crossovers is equal to the expected frequency. If interference is complete (interference = 1), then there are no double crossovers observed. 31 Interference Sample problem: The recombination frequency in region I is 10%, and in region II is 9%. The observed rate of double crossovers encompassing both regions is 0.6%. Calculate the interference. Expected double crossover frequency = (0.1) (0.09) = 0.009 0.006 Coefficient of coincidence = 0.009 = 0.667 Interference = 1 – 0.667 = 0.33 = 33% means you are seeing 33% less dco than you should. due to interference. 32 Next topic DNA Chapter 9 pp 192-204 33...
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This document was uploaded on 02/25/2014.

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