Sources of Variation:

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Sources of Variation Mutation Recombination
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• Mutations I Changes in Chromosome Number and
  Structure
• - Overview

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• Mutations I Changes in Chromosome Number and
  Structure
• - Overview
• 1) A mutation is .

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• Mutations I Changes in Chromosome Number and
  Structure
• - Overview
• 1) A mutation is a change in the genome of a
  cell.

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• Mutations I Changes in Chromosome Number and
  Structure
• - Overview
• 1) A mutation is a change in the genome of a
  cell.
• 2) Evolutionarily important mutations are
  heritable (not somatic). However, the tendency
  for a gene to mutate in somatic tissue (cancer)
  as a result of sensitivity to env conditions may
  be heritable.

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• Mutations I Changes in Chromosome Number and
  Structure
• - Overview
• 3) Changes occur at 4 scales (large to small)
• - Change in the number of SETS of chromosomes
  (change in PLOIDY)
• - Change in the number of chromosomes in a set
  (ANEUPLOIDY trisomy, monosomy)
• - Change in the number/arrangement of genes on a
  chromosome
• - Change in the nitrogenous base sequence within
  a gene
• In general, the LARGER the change, the more
  dramatic (and usually deleterious) the effects.
  If you have a functioning genome, a big change is
  going to be MORE LIKELY to disable it than a
  small change

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• a. Autopolyploidy production of a diploid
  gamete used in reproduction within a species.

Failure of meiosis I or II
2n gamete
3n zygote
Correct meiosis in other parent
1n gamete
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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• a. Autopolyploidy production of a diploid
  gamete used in reproduction within a species.

Errors in mitosis can also contribute, in
hermaphroditic species
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2n
1) Consider a bud cell in the flower bud of a
plant.
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2n
4n
1) Consider a bud cell in the flower bud of a
plant.
2) It replicates its DNA but fails to divide...
Now it is a tetraploid bud cell.
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2n
4n
1) Consider a bud cell in the flower bud of a
plant.
2) It replicates its 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
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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)
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How do we define species? Here, the
tetraploid population is even reproductively
isolated from its own parent speciesSo
speciation can be an instantaneous genetic
event
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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• a. Autopolyploidy production of a diploid
  gamete used in reproduction within a species.
• b. Allopolyploidy fusion of gametes from
  different species (hybridization). These are
  usually sterile because the chromosomes are not
  homologous and cant pair during gamete
  formation. BUT if the chromosomes replicate and
  separate without cytokinesis, they create their
  own homologs and sexual reproduction is then
  possible.

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X
Spartina alterniflora from NA colonized Europe
Spartina maritima native to Europe
Sterile hybrid Spartina x townsendii
Allopolyploidy 1890s
Spartina anglica an allopolyploid and a
worldwide invasive outcompeting native species
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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• 2. Frequency
• Polyploidy is common in plants 50 of
  angiosperm species may be the product of
  polyploid speciation events.

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• 2. Frequency
• Polyploidy is common in plants 50 of
  angiosperm species may be the product of
  polyploid speciation events.
• In vertebrates, polyploidy decreases in
  frequency from fish to amphibians to reptiles,
  and is undocumented in birds. There is one
  tetraploid mammal. (Red viscacha rat).

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• 2. Frequency
• 3. The effect of hermaphrodism

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• 2. Frequency
• 3. The effect of hermaphrodism
• - when the sexes are separate, the rare, random
  mutation of producing a diploid gamete is
  UNLIKELY to occur in two parents simultaneously.
  So, the rare diploid gamete made by one parent
  (karyokinesis without cytokinesis doubling
  chromosome number in a cell) will probably
  fertilize a normal haploid gamete. This produces
  a TRIPLOID which may live, but would be
  incapable of sexual reproduction.

2n
3n
1n
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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• 2. Frequency
• 3. The effect of hermaphrodism
• - unless. the new organism could ALSO produce
  eggs without reduction..clonally and these are
  the rare animals that we see triploid species
  that are composed of females that reproduce
  asexually. (Some may still mate with their
  diploid sibling species so that the sperm
  stimulated the egg to develop but without
  incorporation of sperm DNA.)
• Like this Blue-spotted Salamander A. laterale,
• which has a triploid sister species, A. tremblayi

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C. Inornatus C. neomexicanus C. tigris
Parthenogenetic diploid
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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• 2. Frequency
• 3. The effect of hermaphrodism
• - So, in species with separate sexes,
  polyploidy is probably rare because the typical
  condition would be TRIPLOIDY, which is usually a
  sterile condition.

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• 2. Frequency
• 3. The effect of hermaphrodism
• - So, in species with separate sexes,
  polyploidy is probably rare because the typical
  condition would be TRIPLOIDY, which is usually a
  sterile condition.
• - But in hermaphroditic organisms (like many
  plants), a single mutation can affect BOTH male
  and female gametes.

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• 2. Frequency
• 3. The effect of hermaphrodism
• SO! Polyploidy may be more frequent in plants
  because they are hermaphroditic more often than
  animals especially vertebrates. Most cases of
  polyploidy in animals is usually where triploid
  females survive and reproduce asexually.
• Also, simpler development in plants means they
  may tolerate imbalances better.

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• 1. Mechanisms
• 2. Frequency
• 3. The effect of hermaphrodism
• 4. Evolutionary Importance
• - obviously can be an instant speciation event
• - polyploidy is also a mechanism for genome
  doubling or whole genome duplication
• - this duplication allows for divergence of
  copied gene function and evolutionary innovation.
  Eventually, the copies may be so different that
  they dont really represent duplicates any more
  resulting in diploidization.

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• B. Aneuploidy

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B. Aneuploidy 1. Mechanism Non-disjunction
during gamete formation During either Meiosis I
or II, segregation of (homologs or sister
chromatids) does not occur both entities are
pulled to the same pole.
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B. Aneuploidy 1. Mechanism Non-disjunction
during gamete formation During either Meiosis I
or II, segregation of (homologs or sister
chromatids) does not occur both entities are
pulled to the same pole. This produces gametes
with one more (1n 1) or one less (1n -1)
chromosome than they should have. Subsequent
fertilization with a normal haploid (1n) gamete
produces a trisomy (2n1) or monosomy (2n-1).
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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• B. Aneuploidy
• C. Changes in Gene Number and Arrangement

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• B. Aneuploidy
• C. Changes in Gene Number and Arrangement
• 1. Deletions and Additions

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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• B. Aneuploidy
• C. Changes in Gene Number and Arrangement
• 1. Deletions and Additions
• a. mechanisms
• i. unequal crossing over

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i. Unequal Crossing-Over a. process If
homologs line up askew
A
B
a
b
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i. Unequal Crossing-Over a. process If
homologs line up askew And a cross-over occurs
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i. 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
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i. Unequal Crossing-Over a. process
b. effects - can be bad deletions are
usually bad reveal deleterious
recessives additions can be bad change
protein concentration
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i. 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.)
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i. 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?
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Gene A
Duplicated A
generations
Mutation may even render the protein non-functio
nal
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.
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Mutation may even render the protein non-functio
nal
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.
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If so, then wed 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
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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
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• Mutations I Changes in Chromosome Number and
  Structure
• A. Polyploidy
• B. Aneuploidy
• C. Changes in Gene Number and Arrangement
• 1. Deletions and Additions
• a. mechanisms
• i. unequal crossing over (both)
• ii. Intercalary Deletion

B
A
C
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1. Deletions and Additions a.
mechanisms i. unequal crossing over
(both) ii. Intercalary Deletion
B
A
C
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1. Deletions and Additions a.
mechanisms i. unequal crossing over
(both) ii. Intercalary Deletion
A
C
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1. Deletions and Additions a.
mechanisms i. unequal crossing over
(both) ii. Intercalary Deletion
1. Deletions and Additions a.
mechanisms i. unequal crossing over
(both) ii. Intercalary Deletion -recognized
by the formation of a deletion loop in homolog
during synapsis
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1. Deletions and Additions a.
mechanisms i. unequal crossing over
(both) ii. Intercalary Deletion iii.
Transposons (addition) - transposons are
copied (replicated) independent of the S phase of
interphasethe copy is inserted elsewhere in the
genome. Create homologus regions that lead to
unequal crossing over and duplications
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1. Deletions and Additions a.
mechanisms i. unequal crossing over
(both) ii. Intercalary Deletion iii.
Transposons (addition) - OR, a transposon can
be inserted within a gene, destroying it and
functionally deleting it.
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• VI. Mutation
• Overview
• Changes in Ploidy
• Changes in Aneuploidy (changes in chromosome
  number)
• D. Change in Gene Number/Arrangement
• Deletions and Additions
• Inversion (changes the order of genes on a
  chromosome)

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• VII. Mutation
• A. Changes in Ploidy
• B Changes in Aneuploidy (changes in chromosome
  number)
• C. Change in Gene Number/Arrangement
• Deletions and Additions
• Inversion (changes the order of genes on a
  chromosome)

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• VII. Mutation
• A. Changes in Ploidy
• B Changes in Aneuploidy (changes in chromosome
  number)
• C. Change in Gene Number/Arrangement
• Deletions and Additions
• 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
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• VII. Mutation
• A. Changes in Ploidy
• B Changes in Aneuploidy (changes in chromosome
  number)
• C. Change in Gene Number/Arrangement
• Deletions and Additions
• Inversion (changes the order of genes on a
  chromosome)

Chromosomes are no longer homologous along entire
length
And if a cross-over occurs.
ONE loops to get genes across from each other
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• VII. Mutation
• A. Changes in Ploidy
• B Changes in Aneuploidy (changes in chromosome
  number)
• C. Change in Gene Number/Arrangement
• Deletions and Additions
• Inversion (changes the order of genes on a
  chromosome)

The cross-over products are non-functional, with
deletions AND duplications
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• VII. Mutation
• A. Changes in Ploidy
• B Changes in Aneuploidy (changes in chromosome
  number)
• C. Change in Gene Number/Arrangement
• Deletions and Additions
• 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
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• VII. Mutation
• A. Changes in Ploidy
• B Changes in Aneuploidy (changes in chromosome
  number)
• C. Change in Gene Number/Arrangement
• Deletions and Additions
• 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
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• VII. Mutation
• A. Changes in Ploidy
• B Changes in Aneuploidy (changes in chromosome
  number)
• C. Change in Gene Number/Arrangement
• Deletions and Additions
• Inversion (changes the order of genes on a
  chromosome)
• Translocation

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Translocation Downs. Transfer of a 21 chromosome
to a 14 chromosome
Can produce normal, carrier, and Downs child.
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• VII. Mutation
• A. Changes in Ploidy
• B Changes in Aneuploidy (changes in chromosome
  number)
• C. Change in Gene Number/Arrangement
• D. Change in Gene Structure
• Mechanism 1 Exon Shuffling
• Crossing over WITHIN a gene, in introns, can
  recombine exons within a gene, producing new
  alleles.

Allele a
EXON 1a
EXON 2a
EXON 3a
Allele A
EXON 1A
EXON 2A
EXON 3A
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• VII. Mutation
• A. Changes in Ploidy
• B Changes in Aneuploidy (changes in chromosome
  number)
• C. Change in Gene Number/Arrangement
• D. Change in Gene Structure
• Mechanism 1 Exon Shuffling
• Crossing over WITHIN a gene, in introns, can
  recombine exons within a gene, producing new
  alleles.

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VII. Mutation A. Changes in Ploidy B Changes in
Aneuploidy (changes in chromosome number) C.
Change in Gene Number/Arrangement D. Change in
Gene Structure 1. Mechanism 1 Exon
Shuffling 2. Mechanism 2 Point
Mutations a. addition/deletion frameshift
mutations
Throws off every 3-base codon from mutation point
onward
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VII. Mutation A. Changes in Ploidy B Changes in
Aneuploidy (changes in chromosome number) C.
Change in Gene Number/Arrangement D. Change in
Gene Structure 1. Mechanism 1 Exon
Shuffling 2. Mechanism 2 Point
Mutations a. addition/deletion frameshift
mutations b. substitution
At most, only changes one AA (and may not change
it)
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SOURCES OF VARIATION MUTATION RECOMBINATION ?
?
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RECOMBINATION Independent Assortment
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Independent Assortment produces an amazing amount
of genetic variation. Consider an organism, 2n
4, with two pairs of homologs. They can make 4
different gametes (long Blue, Short Red) (Long
Blue, Short Blue), (Long Red, Short Red), (Long
Red, Short blue). Gametes carry thousands of
genes, so homologous chromosomes will not be
identical over their entire length, even though
they may be homozygous at particular loci. Well,
the number of gametes can be calculated as 2n
or
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Independent Assortment produces an amazing amount
of genetic variation. Consider an organism with
2n 6 (AaBbCc) . There are 2n 8 different
gamete types.
ABC abc Abc abC aBC Abc AbC aBc
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Independent Assortment produces an amazing amount
of genetic variation. Consider an organism with
2n 6 (AaBbCc) . There are 2n 8 different
gamete types. And humans, with 2n 46?
ABC abc Abc abC aBC Abc AbC aBc
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Independent Assortment produces an amazing amount
of genetic variation. Consider an organism with
2n 6 (AaBbCc) . There are 2n 8 different
gamete types. And humans, with 2n 46? 223
8 million different types of gametes. And each
can fertilize ONE of the 8 million types of
gametes of the mate for a total 246 70
trillion different chromosomal combinations
possible in the offspring.
ABC abc Abc abC aBC Abc AbC aBc
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Independent Assortment produces an amazing amount
of genetic variation. And each can fertilize ONE
of the 8 million types of gametes of the mate
for a total 246 70 trillion different
chromosomal combinations possible in the
offspring. YOU are 1 of the 70 trillion
combinations your own parents could have made.
IA creates a huge amount of genetic variation,
and that doesnt include crossing over!!!!
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VII. Mutation A. Changes in Ploidy B Changes in
Aneuploidy (changes in chromosome number) C.
Change in Gene Number/Arrangement D. Change in
Gene Structure E. 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
VARIATION
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SOURCES OF VARIATION MUTATION RECOMBINATION In
dependent Assortment Crossing Over New
combinations of genes on chromosomes
Hey!! That solves my dilemma about how new
variation is produced each generation!! Too bad
Im dead!