# Because sometimes a crossover in one region of the

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

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...
View Full Document

## This document was uploaded on 02/25/2014.

Ask a homework question - tutors are online