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Unformatted text preview: Lecture 9 Lecture 9 Lecture 9 Lecture 9 Lecture 9 By way of review, lets consider the general question of how genetic mapping studies can be used to locate a gene that has been identified by an allele with an interesting phenotype. For example, the CLOCK mutation in mouse was identified as a semi-dominant mutation that disrupts the normal circadian rhythm. This mutation was isolated after mutagenesis of animals with ethyl-nitorosourea and then screening their offspring for abnormal activity at a time when normal mice would be sleeping. Lets assume that we have at our disposal a large number of genetic markers spaced evenly along all of the mouse chromosomes (later in the course we will discuss DNA-based markers which can be found in an almost unlimited number in the mammalian genome) and that we have the capability to screen about 1000 mice for recombinants in a mapping experiment. The question of how precisely we can locate the CLOCK gene can be considered to be a question of the resolving power of a mapping experiment. Two points on a genetic map can only be resolved if a recombination event that separates them can be found. The smallest interval that can be resolved on average if 1000 progeny are screened is 1 recombinant in 1000 which corresponds to a map distance of ~ 0.1 cM on either side of the CLOCK mutation. Thus we would be able to map the CLOCK mutation to an interval of 0.2 cM....
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