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Mutation & genetic variation
Mutations
Mutations
gene – stretch of dna that codes for a distinctive type
of rna or protein
allele – versions of the same gene that differ in their
base sequence
mutation – any change in the base sequence of dna
Types of mutations
Point mutation
Frameshift mutation
Gene duplication
Chromosome inversion
Polyploidy
Point mutation
Point mutations are single base substitutions in DNA
Point mutation
Genetic code
Frameshift mutation
Frameshift mutation
Gene duplication
Gene duplication
Duplicated loci can:
-retain their original function and provide an additional
copy of the parent locus
-gain a new function through mutation & selection
-become functionless pseudogenes
Chromosome inversion
Chromosome inversion
Inversions change gene order and decrease the
frequency of crossing over
As a result, the alleles inside the inversion tend to be
inherited as a unit
Polyploidy
Polyploidy
Polyploid populations are reproductively isolated
from their parental species
Fitness effects of mutation
Mutation rate
Species
Taxon
mutations/genome/
generation
E. coli
bacteria
S. acidocaldarius archaea
S. cerevisiae
fungi
0.0025
0.0018
0.0027
C. elegans
D. melanogaster
M. musculus
H. sapiens
0.0360
0.1400
0.9000
1.6000
roundworm
insect
mammal
mammal
Mutation rate
Mutation rates vary among species because of
differences in the number of cell divisions that take
place prior to gamete formation
Human
Fruit fly
400 cell divisions
25 cell divisions
Polymorphism
If more than one allele exists at a particular locus, a
population is said to be polymorphic at that locus
Polymorphism
One third to one half of all coding loci are polymorphic
in a typical population
Why are populations genetically diverse?
Selectionist theory - genetic diversity maintained by
natural selection
Neutral theory - genetic diversity maintained because
it is not eliminated by selection