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Microbial Genetics (Micr340) Lecture 6 Genetic Analysis
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Isolating Mutants Genetic analysis: study of genes and their functions by creating and analyzing mutants Spontaneous mutation – mutations occur naturally – low frequency Artificial mutagenesis uses UV or chemicals to create mutations in DNA – increasing frequency Agents which cause mutations - mutagens
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Selecting Mutants The process of finding mutants - screening Selective conditions – usually conditions under which either the mutant or the wild type will not be able to multiply to form a colony or a plaque. Positive selection: the mutant but not the wild type can multiply Negative seletion: wild type but not the mutant can multiply
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Positive selection
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Selecting Mutants Enrichment
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Complementation Complementation – a method to determine if mutations are in different genes (allelism)
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Complementation
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Cloning by Complementation
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Recombination Tests Complementation reveals how many genes can be mutated to give a particular phenotype and something about the nature of the mutations Recombination tests give information about where mutations are located in the chromosome Recombination: breakage and rejoining of two DNA molecules in new combinations
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Recombination Most common type of recombination is generalized recombination (or homologous recombination); it occurs between two DNA regions that have same (homologous) sequences This requirement of homologous nature ensures the same order of genes before and after recombination Recombination frequency: the number of recombinant-type progeny over the total progeny
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Marker Rescue Definition: recombination between a piece of introduced DNA and the corresponding region in the chromosome containing a mutation can “rescue” the mutation in the chromosome, restoring the wild type phenotype.
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Marker rescue
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Gene replacement and transgenics Gene replacement: replacement of a normal gene in an organism with a particular mutated allele of the same gene via recombination The process of introducing a predetermined mutation into the DNA of an organism is called “reverse genetics”, the reverse of normal genetic analysis
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