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VI. Mutation
A.
B.
C.
D.
Overview
Changes in Ploidy
Changes in ‘Aneuploidy’ (changes in chromosome number)
Change in Gene Number/Arrangement
VI. Mutation
A. Overview
B. Changes in Ploidy
C. 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
B
a
b
VI. Mutation
A. Overview
B. Changes in Ploidy
C. 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
And a cross-over occurs
A
B
a
b
VI. Mutation
A. Overview
B. Changes in Ploidy
C. 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
And 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
B
A
a
b
VI. Mutation
A. Overview
B. Changes in Ploidy
C. 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 recessives
additions can be bad – change protein concentration
VI. Mutation
A. Overview
B. Changes in Ploidy
C. 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 recessives
additions can be bad – change protein concentration
- can be good:
more of a single protein could be advantageous
(r-RNA genes, melanin genes, etc.)
VI. Mutation
A. Overview
B. Changes in Ploidy
C. 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 recessives
additions 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
generations
Mutation – may even render the protein
non-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.
Gene A
Duplicated A
generations
Mutation – may even render the protein
non-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.
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. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
2. Mechanism #2: Inversion (changes the order of genes on a chromosome)
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
2. Mechanism #2: Inversion (changes the order of genes on a chromosome)
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
2. Mechanism #2: Inversion (changes the order of genes on a chromosome)
Chromosomes are no longer homologous along entire length
B-C-D on top
d-c-b on bottom
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
2. 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 crossover occurs….
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
2. Mechanism #2: Inversion (changes the order of genes on a chromosome)
The cross-over
products are nonfunctional, with
deletions AND
duplications
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
2. 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. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
2. 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 ‘coadapted gene complex’
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Mechanism #1: Unequal Crossing-Over
2. 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. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
E. 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. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
E. 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 1A
EXON 2a
EXON 3a
Allele “α”
EXON 1a
EXON 2A
EXON 3A
Allele “ά”
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
E. Change in Gene Structure
1. Mechanism #1: Exon Shuffling
2. Mechanism #2: Point Mutations
a. addition/deletion: “frameshift” mutations
Normal
Mutant: A inserted
…C G T G T A C G T ….
…G C A C A U G C A …
ARG
HIS
ALA
DNA
m-RNA
…C G T A G T A C G T ….
…G C A U C A U G C A …
ARG
SER
CYS
Throws off every 3-base codon from mutation point onward
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
E. Change in Gene Structure
1. Mechanism #1: Exon Shuffling
2. Mechanism #2: Point Mutations
a. addition/deletion: “frameshift” mutations
b. substitution
Normal
Mutant: A for G
…C G T G T A C G T ….
…G C A C A U G C A …
ARG
HIS
ALA
DNA
m-RNA
…C G T A T A C G T ….
…G C A U A U G C A …
ARG
TYR
ALA
At most, only changes one AA (and may not change it…)
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
E. Change in Gene Structure
F. Summary
MUTATION:
-New Genes:
point mutation
exon shuffling
RECOMBINATION:
- New Genes:
crossing over
-New Genotypes:
crossing over
independent assortment
Causes of Evolutionary Change
V A R I A T I O N
Sources of Variation
Natural Selection
Mutation (polyploidy can make new
species)