Transcript Slide 1

VI. Mutation
A. Overview
B. Changes in Ploidy
- These are the most dramatic changes, adding a whole SET of chromosomes
1. Mechanism #1: Complete failure of Meiosis
2. Mechanism #2: Failure of Mitosis in Gamete-producing Tissue
2n
1) Consider a bud cell in
the flower bud of a plant.
2n
1) Consider a bud cell in
the flower bud of a plant.
4n
2) It replicates it’s DNA
but fails to divide... Now
it is a tetraploid bud cell.
2n
1) Consider a bud cell in
the flower bud of a plant.
3) A tetraploid flower develops
from this tetraploid cell; eventually
producing 2n SPERM and 2n EGG
4n
2) It replicates it’s DNA
but fails to divide... Now
it is a tetraploid bud cell.
2n
1) Consider a bud cell in
the flower bud of a plant.
4n
2) It replicates it’s DNA
but fails to divide... Now
it is a tetraploid bud cell.
3) A tetraploid flower develops
from this tetraploid cell; eventually
producing 2n SPERM and 2n EGG
4) If it is self-compatible, it can mate
with itself, producing 4n zygotes
that develop into a new 4n species.
Why is it a new species?
How do we define ‘species’?
“A group of organisms that reproduce with one another and are
reproductively isolated from other such groups”
(E. Mayr – ‘biological species concept’)
How do we define ‘species’?
Here, the tetraploid population is even reproductively isolated from its
own parent species…So speciation can be an instantaneous genetic event…
2n
4n
4n
1n
2n
2n
3n
Zygote
1n
2n
Gametes
Triploid is a dead-end…
so species are separate
Zygote
Gametes
VI. Mutation
A. Overview
B. Changes in Ploidy
- These are the most dramatic changes, adding a whole SET of chromosomes
1. Mechanism #1: Complete failure of Meiosis
2. Mechanism #2: Complete failure of Mitosis
3. The Frequency of Polyploidy
For reasons we just saw, we might expect polyploidy to occur more frequently in
hermaphroditic species, because the chances of ‘jumping’ the triploidy barrier to
reproductive tetraploidy are more likely. Over 50% of all flowering plants are
polyploid species; many having arisen by this duplication of chromosome number
within a lineage.
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)
2. Human Examples
a. trisomies
Trisomy 21 – “Downs’ Syndrome”
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)
2. Human Examples
a. trisomies
Trisomy 21 – “Downs’ Syndrome”
Trisomy 18 – Edward’s Syndrome
Trisomy 13 – Patau Syndrome
Some survive to birth
Trisomy 9
Trisomy 8
Trisomy 22
Trisomy 16 – most common – 1% of pregnancies – always aborted
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)
Extreme effects listed below;
2. Human Examples
most show a phenotype within
a. trisomies
the typical range for XY males
47, XXY – “Klinefelter’s Syndrome”
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)
2. Human Examples
a. trisomies
47, XXX – “Triple-X Syndrome”
No dramatic effects on the
phenotype; may be taller.
In XX females, one X shuts
down anyway, in each cell
(Barr body).
In triple-X females, 2 X’s shut
down.
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)
2. Human Examples
a. trisomies
47, XYY – “Super-Y Syndrome”
Often taller, with scarring
acne, but within the
phenotypic range for XY males
VI. Mutation
A. Overview
B. Changes in Ploidy
C. Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)
2. Human Examples
b. monosomies
45, XO– “Turner’s Syndrome” (the only human monosomy to survive to birth)
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: Translocation
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
…T C C G T A C G T ….
…A G G C A U G C A …
ARG
HIS
ALA
DNA
m-RNA
…T C C A G T A C G T ….
…A G G 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
… T C C G T A C G T ….
…A G G C A U G C A …
ARG
HIS
ALA
DNA
m-RNA
…T C C A T A C G T ….
…A G G 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)
Modern Evolutionary Biology
I. Population Genetics
A. Overview
Agents of Change
Mutation
N.S.
Recombination
- crossing over
- independent assortment
VARIATION
Sources of Variation
mutation
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
G. Hardy and W. Weinberg
1. Definitions
- Evolution: a change in the genetic structure of a population
- Population: a group of interbreeding organisms that share a common gene
pool; spatiotemporally and genetically defined
- Gene Pool: sum total of alleles held by individuals in a population
- Genetic structure: Gene array and Genotypic array
- Gene/Allele Frequency: % of alleles at a locus of a particular type
- Gene Array: % of all alleles at a locus: must sum to 1.
- Genotypic Frequency: % of individuals with a particular genotype
- Genotypic Array: % of all genotypes for loci considered; must = 1.
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
1. Definitions
2. Basic Computations
Individuals
AA
Aa
aa
70
80
50
(200)
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
1. Definitions
2. Basic Computations
AA
Aa
aa
Individuals
70
80
50
(200)
Genotypic
Array
70/200 =
0.35
80/200 = .40
50/200 =
0.25
=1
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
1. Definitions
2. Basic Computations
AA
Aa
aa
Individuals
70
80
50
(200)
Genotypic
Array
70/200 =
0.35
80/200 = .40
50/200 =
0.25
=1
''A' alleles
140
80
0
220/400 =
0.55
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
1. Definitions
2. Basic Computations
AA
Aa
aa
Individuals
70
80
50
(200)
Genotypic
Array
70/200 =
0.35
80/200 = .40
50/200 =
0.25
=1
''A' alleles
140
80
0
220/400 =
0.55
'a' alleles
0
80
100
180/400 =
0.45
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
1. Definitions
2. Basic Computations
- Determining the Gene Array from the Genotypic Array
a. f(A) = f(AA) + f(Aa)/2 = .35 + .4/2 = .35 + .2 = .55
b. f(a) = f(aa) + f(Aa)/2 = .25 + .4/2 = .25 + .2 = .45
KEY: The Gene Array CAN ALWAYS be computed from the genotypic array; the
process just counts alleles instead of genotypes. No assumptions are made when you do
this.
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
1. Goal:
Describe what the genetic structure of the population would be if there were
NO evolutionary change – if the population was in equilibrium.
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
1. Goal:
Describe what the genetic structure of the population would be if there were
NO evolutionary change – if the population was in equilibrium.
For a population’s genetic structure to remain static, the following must be
true:
- random mating
- no selection
- no mutation
- no migration
- the population must be infinitely large
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
2.Example:
Initial
genotypic freq.
Gene freq.
Genotypes, F1
Gene Freq's
Genotypes, F2
AA
Aa
aa
0.4
0.4
0.2
1.0
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
2.Example:
Initial
genotypic freq.
Gene freq.
Genotypes, F1
Gene Freq's
Genotypes, F2
AA
Aa
aa
0.4
0.4
0.2
f(A) = p = .4 + .4/2 = 0.6
1.0
f(a) = q = .2 + .4/2 = 0.4
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
2.Example:
Initial
genotypic freq.
Gene freq.
Genotypes, F1
Gene Freq's
Genotypes, F2
AA
Aa
aa
0.4
0.4
0.2
f(A) = p = .4 + .4/2 = 0.6
p2 = .36
2pq = .48
1.0
f(a) = q = .2 + .4/2 = 0.4
q2 = .16
= 1.00
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
2.Example:
Initial
genotypic freq.
Gene freq.
Genotypes, F1
Gene Freq's
Genotypes, F2
AA
Aa
aa
0.4
0.4
0.2
f(A) = p = .4 + .4/2 = 0.6
p2 = .36
2pq = .48
1.0
f(a) = q = .2 + .4/2 = 0.4
q2 = .16
= 1.00
f(A) = p = .36 + .48/2 = 0.6
f(a) = q = .16 + .48/2 = 0.4
p2 = .36
q2 = .16
2pq = .48
= 1.00
After one generation with these conditions, the population equilibrates
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
2.Example
3. Utility:
If no populations meets these conditions explicitly, how can it be useful?
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
2.Example
3. Utility:
If no populations meets these conditions explicitly, how can it be useful?
For comparison, like a “perfectly balanced coin”
Initial
genotypic freq.
Gene freq.
HWE
expections
AA
Aa
aa
0.5
0.2
0.3
f(A) = p = .5 + .2/2 = 0.6
p2 = .36
2pq = .48
1.0
f(a) = q = .3 + .2/2 = 0.4
q2 = .16
CONCLUSION:The real population is NOT in HWE.
= 1.00
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
3. Utility:
- if a population is NOT in HWE, then one of the assumptions must be violated.
Sources of Variation
Recombination
- crossing over
VARIATION
Mutation
Agents of Change
- independent assortment
So, if NO AGENTS are acting on a population, then it
will be in equilibrium and WON'T change.
N.S.
Drift
Migration
Mutation
Non-random Mating
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
D. Deviations from HWE
1. mutation
1. Consider a population with:
f(A) = p = 0.6
f(a) = q = 0.4
2. Suppose 'a' mutates to 'A' at a realistic rate of:
μ = 1 x 10-5
3. Well, what fraction of alleles will change?
'a' will decline by: qm = .4 x 0.00001 = 0.000004
'A' will increase by the same amount.
f(A) = p1 = 0.600004
f(a1) = q = 0.399996
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
D. Deviations from HWE
1. mutation
2. migration
p2 = 0.7
p1 = 0.2
q2 = 0.3
q1 = 0.8
suppose migrants immigrate at a rate
such that the new immigrants represent
10% of the new population
Modern Evolutionary Biology
I. Population Genetics
A. Overview
B. The Genetic Structure of a Population
C. The Hardy-Weinberg Equilibrium Model
D. Deviations from HWE
1. mutation
2. migration
p2 = 0.7
p1 = 0.2
q2 = 0.3
q1 = 0.8
M = 10%
p(new) = p1(1-m) + p2(m)
= 0.2(0.9) + 0.7(0.1)
= 0.18 + 0.07 = 0.25