Lecture 7- Origin of Variation cont’d
DNA replication error results in an AT base pair being replaced by a GC base pair- IS this necessarily a mutation?
- Yes; it is a change in the double stranded DNA sequence
- We don’t care about the consequence eg. altering an amino acid. Just any change in the sequence.
- If a change is not a double stranded change, it is not a mutation, it is just called damage
• Difference between DNA damage and mutation
- If the DNA replication error is a double stranded change, it is a mutation. Otherwise it is simply damage.
• Different types of genomic variation among humans
- SNPs (single base pair substitution) arise from replication errors resulting in more diffs.
- CNVs (copy number variation)
- Not all variation is inherited from parents
• Why African populations have more unique SNPs than other populations (ie. Asian or
- Have much more variable genomes than the other decendants. African populations are older aka humans
evolved there and these populations have had much more time to diverge and become diff.
• Difference between insertion sequences, transposons and retrotransposons
Insertion sequences Transposons Retrotransposons
How it works Short sequence of DNA “Cut and paste”- Copy is made of RNA
containing only genes transposon cut and instead of DNA; RNA
needed for moved to a diff copies then transcribed
transposition; bounded location, base pairs fill back into DNA using
at both ends by in the spaces. reverse transcriptase
sequences of and then inserted into
nucleotides in reversed new locations in the
orientations (IRs). genome.
Other effects Cause mutations;
change amount of DNA
in genome of cell (and
if in gametes, in
genome of offspring)
• Why mobile elements are considered to be biological mutagens
- They create a double stranded change in the DNA sequence.
• Role of tautomeric shifts in mutagenesis