Introduction to Genetic Analysis 154

Introduction to Genetic Analysis 154 - 44200_05_p151-184...

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153 5.1 Working with microorganisms and their chromosomes are so small, possible sexlike fusion events are difFcult to observe, even with a micro- scope. Therefore the general approach has been a genetic one based on the detection of recombinants. The logic is that if different genomes ever do get together, they should occasionally produce recombinants. Con- versely, if recombinants are detected, with marker A from one parent and B from another, then there must have been some type of “sexual” union. Hence, even though bacteria and phages do not undergo meiosis, the approach to the genetic analysis of these forms is sur- prisingly similar to that for eukaryotes. The opportunity for genetic recombination in bacte- ria can arise in several different ways, but in all cases two DNA molecules are brought together. The possibilities are outlined in ±igure 5-1. The Frst process to be exam- ined here is conjugation: one bacterial cell transfers DNA in one direction to another cell by direct cell-to-cell con- tact. The transferred DNA may be part of or all the bacte- rial genome, or it may be an extragenomic DNA element called a plasmid. A genomic fragment may recombine with the recipient’s chromosome after entry. A bacterial cell can also acquire a piece of DNA
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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