Lesson 6: Mutation Flashcards
- genetic substrate for natural selection
- raw material for evolution
mutation
What reduces variation?
- genetic drift in finite populations
- reduction in allelic diversity
- reduction in heterozygosity (inbreeding)
Sources of allelic variation
mutation
Sources of Genotypic Variation
Sex (meiosis)
heritable variation changes in gene expression without changes in genetic code
epigenetic inheritance
if there is no __ __, neither genetic drift nor natural selection would be able to change allelic frequencies, because there would be nothing to change
genetic variation
requires genetic variation upon which it could act
natural selection
- change in genetic code
- new alleles and/or new genes
mutations
Mutations: new alleles
nucleotide substitutions, insertions, deletions
Mutations: new genes
- gene duplication or deletions
- exon shuffling
- horizontal gene transfer (not always considered mutation)
Types of Mutations
- chromosomal duplications or deletions
- deletions of large chromosomal regions
- chromosomal inversions
- whole genome duplication
- no novel alleles
- only novel genotypes
sex
Sex
- genetic recombination
- random mating
shuffling of combinations of alleles along a chromosome
genetic recombination
shuffling of combinations of haploid chromosomes into new genotypes
random mating
Types of Mutations:
AT THE NUCLEOTIDE LEVEL
- single nucleotide substitutions
- insertions
- deletion
mutation at the nucleotide level is also called…?
point mutations
types of single nucleotide substitutions
- transitions
- transversions
Types of Mutations:
AT THE “GENE” LEVEL
- gene insertions
- gene deletions
- exon shuffling
Types of gene insertions
- gene duplication
- transposons
- horizontal gene transfer
Types of gene deletions
- pseudogenization
- transposons
Types of Mutations:
AT THE CHROMOSOME LEVEL
chromosome
- duplications
- deletions
- inversions
- fusions
Types of Mutations:
AT THE GENOME LEVEL
- autopolyploidization
- allopolyploidization
changes in the actual coding region of the gene
structural
structural
- primary
- secondary, tertiary, quaternary structure
primary structure
amino acid composition (amino acid substitutions)
changes in gene regulation
regulatory
regulatory
gene expression
gene expression
- transcription
- RNA processing
- translation
single nucleotide change
point mutations
Causes of Point mutations
- DNA replication error during mitosis or meiosis
- Error in repair of sites damaged by mutagens
nucleotide composition
- phosphate group
- nitrogenous base
- 5’-carbon sugar
types of nitrogenous base
- purines
- pyrimidines
purines mutate to purines
(ex. Adenine -> Guanine)
transitions
link between sugar and phosphate
phosphodiester linkage
purines mutate to pyrimidines, and vice versa
(ex. Adenine -> Cytosine)
transversions
in the case of amino acids, what mutation position lead to amino acid change
position 1 and 2
mutations that lead to amino acid changes (Position 1,2)
nonsynonymous substitutions (missense mutation)
mutations that do not lead to amino acid change (often position 3)
synonymous substitutions (silent mutation)
- process by which a region of DNA coding for a gene is copied
- can occur as the result of an error in recombination or through a retrotransposition event
- genes are often immune to the selective pressure under which genes normally exist.
Gene duplication
Gene duplications could happen due to..?
- “slippage” during DNA replication
- unequal crossing over during genetic recombination (meiosis)
- repeated segments are adjacent
- often result from unequal crossing-over due to mispairing of homologous chromosomes during meiotic recombination
tandem duplications
cause of mutation (gene duplication)
unequal crossing over
- segment of DNA that structurally resembles a gene but is not capable of coding for a protein
- most often derived from genes that have lost their protein-coding ability due to accumulated mutations that have occurred over the course of evolution.
pseudogenes
Fate of duplicated genes
- nonfunctionalization
- neofunctionalization
- subfunctionalization
loss of function of extra gene copy
nonfunctionalization
new function of extra gene copy
neofunctionalization
partition of function between the gene copies
subfunctionalization
different exons either within a gene or between two nonallelic genes are mixed (end up with new protein)
exon shuffling
chromosomal alterations
chromosome
- duplications
- deletions
- inversions
- fusions
- DNA sequence that can change its relative position within the genome
- “jumping genes”
transposable elements (transposons)
discovered transposons or jumping genes
Barbara McClintock
transposition “copy and paste”
retrotransposons
transposition “cut and paste”
DNA transposons
generation of more than two pairs of homologous chromosomes due to failure of reduction of chromosomes during cell division (mitosis or meiosis)
polyploidization
vary among species and can vary among populations within a species
mutation rates
rate of mutations in HIV
high
in most species, mutations rate is relatively __
low
when are elevated mutations rates advantageous
when faced with novel or stressful environments (especially in bactera)
mutation rate is much higher in __ genomes relative to nuclear genomes
organelle
why is mutation rate much higher in organelle genomes
due to lack of DNA repair enzymes
mutation rate is elevated in some parts of the genome
mutational “hot spots”
Evolutionary causes of mutation rate variation
- generation-time hypothesis
- metabolic-rate hypothesis
- DNA repair hypothesis
- genetic drift interfere with selection
- groups with shorter generations evolve faster because they experience more rounds of germ-cell divisions during an arbitrary unit of time
- more rounds of germ-line divisions mean additional DNA synthesis and extra opportunities for mutations that are due to DNA replication errors
generation-time hypothesis
- mutation rate that is due to endogenous or exogenous mutagens, such as oxygen radicals
- argues that groups with higher rates produce more free radicals, which leads to greater DNA damage and faster mutation and evolutionary rates
metabolic-rate hypothesis
- groups with better DNA repair systems
- more mutations are corrected before transmission
- reduces mutational output
DNA repair hypothesis
- in smaller populations, selection is less efficient, so fewer deleterious mutaitons are removed from the genome
- increased presence of deleterious mutations in smaller populations
genetic drift interfere with selection
most mutations in mutlicellular eukaryotes are __ with no effect on fitness, as most of the genome is nonfunctional
neutral
most mutations that affect functional genes are __
harmful
persist longer in population because it takes longer to select them out
mildly deleterious mutations
selection for favorable mutations leads to __
adaptation
mutations that matter, in evolutionary sense, are those that..?
passed on to next generation (occur in “germ line”)
mutations that do not get passed on to the next generation
in somatic cells
germ line that accumulates more mutations
male germ line
discussed the exponential growth of mutations in the male germ line
James Crow
mutation rate is constant with age
female germ line
mutation rate increases exponentially with age
male germ line
preferential or non-random use of synonymous codons
Codon usage bias
what are the sources of genetic variation
- mutation
- genetic recombination
Mutation that created a STOP codon
Nonsense mutation
