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Segmental, Componential, & Contextual Changes

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Presentation on theme: "Segmental, Componential, & Contextual Changes"— Presentation transcript:

1 Segmental, Componential, & Contextual Changes
Dan Graur The material basis of heredity

2 Segmental = involving two or more adjacent nucleotides
Componential = affecting gene content Contextual = affecting gene context

3 Point substitution

4 Reciprocal Recombination

5 Gene Conversion

6 Tandem duplication

7 Deletion

8 Conservative transposition

9 Duplicative transposition

10 Inversion

11 Horizontal gene transfer

12 DNA duplication (by size)
1. internal gene duplication 2. complete gene duplication 3. partial chromosomal duplication (partial polysomy) 4. complete chromosomal duplication (polysomy) 5. genome duplication (polyploidy)

13 Almost invariably deleterious. polysomy rare partial polysomy
Deleteriousness may be determined by the mode of reproduction and sex-determination. common polyploidy Almost invariably deleterious. polysomy rare partial polysomy Deleterious if expression is determined by gene number. frequent whole gene Deleterious if it affects reading frame. very frequent partial gene Possible Effects on Fitness Mutational Occurrence Extent of DNA Duplication

14 chromosomal duplication
Polysomy: Complete chromosomal duplication deleterious e.g., trisomy 13

15 Partial Polysomy: Partial chromosomal duplication
deleterious Partial Trisomy 16q+ A partial duplication of 16q from band q13 to q24

16 DNA duplication 1. internal gene duplication
2. complete gene duplication 3. partial chromosomal duplication 4. complete chromosomal duplication 5. genome duplication

17 Equal & Unequal Crossing Over
The main mechanism responsible for gene duplication is unequal crossing-over.

18 Variation begets Variation

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