Post on 02-Oct-2015
description
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