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Segmental, Componential, & Contextual Changes. Dan Graur. Segmental = involving two or more adjacent nucleotides Componential = affecting gene content Contextual = affecting gene context. Point substitution. Reciprocal Recombination. Gene Conversion. Tandem duplication. Deletion. - PowerPoint PPT Presentation
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Dan Graur
Segmental, Segmental, Componential, & Componential, &
Contextual Contextual ChangesChanges
• Segmental = involving two or more adjacent nucleotides• Componential = affecting gene content• Contextual = affecting gene context
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Point substitution
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ReciprocalRecombination
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Gene Conversion
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Tandem duplication
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Deletion
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Conservativetransposition
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Duplicativetransposition
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Inversion
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Horizontalgene
transfer
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DNA duplication (by DNA duplication (by size)size)
1. internal gene duplication2. complete gene duplication3. partial chromosomal duplication (partial polysomy)4. complete chromosomal duplication (polysomy)5. genome duplication (polyploidy)
Deleteriousness may be determined by the mode of reproduction
and sex-determination.
commonpolyploidy
Almost invariably deleterious.
commonpolysomy
Almost invariably deleterious.
rarepartial polysomy
Deleterious if expression is
determined by gene number.
frequentwhole gene
Deleterious if it affects reading
frame.
very frequent
partial gene
Possible Effects onFitness
Mutational
Occurrence
Extent of DNA Duplication
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Polysomy: CompletePolysomy: Completechromosomal duplicationchromosomal duplication
deleteriousdeleterious e.g., trisomy 13
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Partial Polysomy: PartialPartial Polysomy: Partialchromosomal duplicationchromosomal duplication
deleteriousdeleterious
Partial Trisomy 16q+
A partial duplication of 16q from A partial duplication of 16q from band q13 to q24band q13 to q24
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DNA duplication1. internal gene duplication
2. complete gene duplication
3. partial chromosomal duplication
4. complete chromosomal duplication
5. genome duplication
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Equal & Unequal Crossing Over
The main mechanism responsible for gene duplication is unequal crossing-over.
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VariatioVariationn begets begets VariatioVariatio
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