Origins of variation Link between DNA and phenotype Sequence variation

errors in replication tautomeric shifts deamination and depurination radiation

Structural variation insertions, deletions, duplications, inversions mobile elements

Consequence of duplication: Gene families

Link between DNA and phenotype sequences of nucleotides

code for amino acids

transcription & translation

polypeptide proteins

cell structures, communication molecules,

enzymes, transporters, etc.

function as

changes in the nucleotide sequence can affect the coded protein, giving rise to different alleles

Fig. 13.6

Mutation double-stranded change in DNA sequence

A

T

G

C

A

T

A

G

G

C

C

G

A

T

G

C

A

T

C

G

G

C

C

G

A

T

G

C

A

T

A

T

G

C

C

G

A

T

G

C

A

T

A

G

G

C

C

G

original DNA DNA

damage

mutation

no change

Sequence variation small changes in nucleotide sequence (e.g. SNP)

1. Tautomeric shifts

Animation

Figures: http://www.bio.miami.edu/dana/250/250S12_14.html; http://www.studyblue.com/notes/note/n/chapter-14/deck/1327947

spontaneous shift between constitutional isomers

of bases, resulting in alternative H-bonding pattern

normal pairing of A&T

abnormal

pairing of G&T

Sequence variation 2. Deamination

http://bio3400.nicerweb.net/Locked/media/ch15/

removal of an amine group from a base,

resulting in altered H-bonding pattern

Sequence variation

Figure: http://www.ncbi.nlm.nih.gov/books/NBK26879/

disruption of bond

between purine

and deoxyribose,

resulting in an

apurinic site

3. Depurination

Sequence variation 4. UV radiation

energy is absorbed by pyrimidine rings, altering

bonding patterns and forming dimers

Figure: McGraw Hill

Structural variation changes in the physical arrangement of genes (or nucleotide sequences) on chromosomes

deletion/

insertion

Fig. 12.11 duplication

inversion

reciprocal

translocation

Structural variation

Slippage in replication

Figure: Hurles, M. 2004. Gene Duplication: the Genomic Trade in Spare Parts. 10.1371/journal.pbio.0020206

newly synthesized DNA

strand slips, looping out

bases

often in tandem repeat regions

may result in triplet repeat diseases

-Fragile X (CGG)

-Huntingtons (CAG)

Animation

Structural variation

DNA segments that move within* the genome

transposase identifies inverted repeat sequences (IR) at end of element

cut/copy and paste to other chromosomes may include moving genes between IRs

Figure 9.17

Mobile elements

Gene families groups of homologous genes that are likely to have similar functions

http://blog.arrowheadalpines.com/2011/07/sciency-answers-variegation-part-2.html