Segmental Componential Contextual Changes Dan Graur 1 Segmental

Segmental, Componential, & Contextual Changes Dan Graur 1

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

Point substitution 3

Reciprocal Recombination 4

Gene Conversion 5

Tandem duplication 6

Deletion 7

Conservative transposition 8

Duplicative transposition 9

Inversion 10

Horizontal gene transfer 11

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) 12

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

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

Partial Polysomy: Partial chromosomal duplication deleterious Partial Trisomy 16 q+ A partial duplication of 16 q from band q 13 to q 24 15

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

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

Variation begets Variation 18