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Lecture 5

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Biology 1001A
Tom Haffie

September 22/2011 Biology Chapter 10- Genetic Recombination (Lecture 5-6) 10.1- Mechanism of Genetic Recombination • Genetic Recombination requires two DNA molecules that differ from one another in at least two places, a mechanism for bringing the DNA molecules into close proximity and a collection of enzymes to ‘cut,’ and ‘paste’ the DNA back together. • Homologous- Regions of DNA that are similar but not identical o HOMOLOGY allows DNA on different molecules to line up and recombine precisely. • Enzymatic cutting and pasting of both DNA backbones from each of the two DNA molecules is required for each recombination event. o Cutting and pasting four DNA backbones results in one recombination event Q- WHAT WOULD HAPPEN IF TWO CIRCULAR DNA MOLECULES WERE INVOLVED IN A SINGLE REOMBINATION EVENT? A-TWO CIRCULAR MOLECULES ‘FUSE’ TOGETHER AS A RESULT OF A SINGLE RECOMBINATION EVENT Rare mutations in a DNA sequence of a gene give rise to new alleles. Without this phenomenon there would be no evolution! 10.2- Genetic Recombination in Bacteria • Data showed that, for particular bacteria, there are mechanisms to bring DNA from different cells together to recombine and create genetically different offspring • Study of bacterial recombination requires detectable genetic differences between strains • Lederberg and Tatum created strains that were different in their ability to manufacture certain amino acids and vitamins o Replica plating transfers cells from complete media to minimal media where auxotrophs fail to grow. o The picture provides us with experimental evidence for genetic recombination in bacteria o In bacteria, the DNA of the bacterial chromosome may recombine with DNA brought into close proximity from another cell • Three primary mechanisms bring DNA into bacterial cells from the outside: conjugation, transformation, and transduction 1. Conjugation-The basis of a kind of sexual reproduction in bacteria  Instead of fusing, bacterial cells conjugate  Contact each other by a long tubular structure called a sex pilus and then form a cytoplasmic bridge  Part or all of the DNA of one cell moves into the other
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