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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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