VI. Mutation A.Overview B.Changes in Ploidy C.Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement
Jan 26, 2016
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
a. process:
If homologs line up askew:
A
a b
B
A
a b
B
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
a. process:
If homologs line up askewAnd a cross-over occurs
A a b
B
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
a. process:
If homologs line up askewAnd a cross-over occurs Unequal pieces of DNA will be exchanged… the A locus has been duplicated on the lower chromosome and deleted from the upper chromosome
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
a. process: b. effects:
- can be bad:deletions are usually bad – reveal deleterious recessivesadditions can be bad – change protein concentration
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
a. process: b. effects:
- can be bad:deletions are usually bad – reveal deleterious recessivesadditions can be bad – change protein concentration
- can be good:more of a single protein could be advantageous (r-RNA genes, melanin genes, etc.)
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
a. process: b. effects:
- can be bad:deletions are usually bad – reveal deleterious recessivesadditions can be bad – change protein concentration
- can be good:more of a single protein could be advantageous (r-RNA genes, melanin genes, etc.)
source of evolutionary novelty (Ohno hypothesis - 1970)where do new genes (new genetic information) come from?
Gene A Duplicated A
Mutation – may even render the proteinnon-functional
But this organism is not selected against, relative to others in the population that lack the duplication, because it still has the original, functional, gene.
generations
Mutation – may even render the proteinnon-functional
Mutation – other mutations may render the protein functional in a new way
So, now we have a genome that can do all the ‘old stuff’ (with the original gene), but it can now do something NEW. Selection may favor these organisms.
Gene A Duplicated A
generations
If so, then we’d expect many different neighboring genes to have similar sequences. And non-functional pseudogenes (duplicates that had been turned off by mutation).These occur – Gene Families
And, if we can measure the rate of mutation in these genes, then we can determine how much time must have elapsed since the duplication event…
Gene family trees…
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1.Mechanism #1: Unequal Crossing-Over2.Mechanism #2: Inversion (changes the order of genes on a chromosome)
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1.Mechanism #1: Unequal Crossing-Over2.Mechanism #2: Inversion (changes the order of genes on a chromosome)
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1.Mechanism #1: Unequal Crossing-Over2.Mechanism #2: Inversion (changes the order of genes on a chromosome)
Chromosomes are no longer homologous along entire length
B-C-D on topd-c-b on bottom
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1.Mechanism #1: Unequal Crossing-Over2.Mechanism #2: Inversion (changes the order of genes on a chromosome)
Chromosomes are no longer homologous along entire length
ONE “loops” to get genes across from each other…
And if a cross-over occurs….
The cross-over products are non-functional, with deletions AND duplications
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1.Mechanism #1: Unequal Crossing-Over2.Mechanism #2: Inversion (changes the order of genes on a chromosome)
The only functional gametes are those that DID NOT cross over – and preserve the parental combination of alleles
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1.Mechanism #1: Unequal Crossing-Over2.Mechanism #2: Inversion (changes the order of genes on a chromosome)
Net effect: stabilizes sets of genes. This allows selection to work on groups of alleles… those that work well TOGETHER are selected for and can be inherited as a ‘co-adapted gene complex’
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1.Mechanism #1: Unequal Crossing-Over2.Mechanism #2: Inversion (changes the order of genes on a chromosome)
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/Arrangement
1.Mechanism #1: Unequal Crossing-Over2.Mechanism #2: Inversion (changes the order of genes on a chromosome)3.Mechanism #3: Translocation (gene or genes move to another homologous set)
Translocation Downs.
Transfer of a 21 chromosome to a 14 chromosome
Can produce normal, carrier, and Down’s child.
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/ArrangementE. Change in Gene Structure
1.Mechanism #1: Exon Shuffling
Crossing over WITHIN a gene, in introns, can recombine exons within a gene, producing new alleles.
EXON 1a EXON 2a EXON 3a Allele “a”
EXON 1A EXON 2A EXON 3A Allele “A”
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/ArrangementE. Change in Gene Structure
1.Mechanism #1: Exon Shuffling
Crossing over WITHIN a gene, in introns, can recombine exons within a gene, producing new alleles.
EXON 1a EXON 2a EXON 3a Allele “a”
EXON 1A EXON 2A EXON 3A Allele “A”
EXON 2a EXON 3aEXON 1A
EXON 2A EXON 3AEXON 1a
Allele “α”
Allele “ά”
Throws off every 3-base codon from mutation point onward
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/ArrangementE. Change in Gene Structure 1. Mechanism #1: Exon Shuffling 2. Mechanism #2: Point Mutations
a. addition/deletion: “frameshift” mutations
…C G T G T A C G T ….
Normal
…G C A C A U G C A …
ARG HIS ALA
Mutant: A inserted
…C G T A G T A C G T ….
…G C A U C A U G C A …
ARG SER CYS
DNA
m-RNA
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/ArrangementE. Change in Gene Structure 1. Mechanism #1: Exon Shuffling 2. Mechanism #2: Point Mutations
a. addition/deletion: “frameshift” mutationsb. substitution
At most, only changes one AA (and may not change it…)
…C G T G T A C G T ….
Normal
…G C A C A U G C A …
DNA
m-RNA
ARG HIS ALA
Mutant: A for G
…C G T A T A C G T ….
…G C A U A U G C A …
ARG TYR ALA
VI. MutationA.OverviewB.Changes in PloidyC.Changes in ‘Aneuploidy’ (changes in chromosome number)D. Change in Gene Number/ArrangementE. Change in Gene StructureF. Summary
Sources of Variation Causes of Evolutionary Change
MUTATION: Natural Selection -New Genes: point mutation Mutation (polyploidy can make new exon shuffling species)
RECOMBINATION: - New Genes: crossing over -New Genotypes: crossing over independent assortment