Download Polyploidy

Polyploidy
…more than two haploid sets of chromosomes
are present,
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2n = diploid,
3n = triploid,
4n = tetraploid,
etc.
Amphidiploid
…double diploid,
2n1 + 2n2
…have balanced gametes of the type n1 + n2,
these gametes fuse to make fertile 2n1 + 2n2.
Allopolyploidy Applications
B. oleracea (cabbage, cauliflower, Brocolli, kale, etc.)
2n = 18
n=9
B.
n1napas
+ n2 =( 19
Oil rape, canola oil)
2n1 + 2n2 = 38
n = 10
B. campestris (turnip, turnip rape)
2n = 20
amphidiploid
4n x 2n = 3n?
• The creation of triploids
can be accomplished by
crossing a tetraploid
with a diploid,
• Most triploid
individuals are sterile.
Generation of a Triploid Cells
Meiosis in a Triploid Organism
Why Wouldn’t this work?
Environmental Applications?
grass carp
(Ctenopharyngodon idella)
• Triploid grass carp prefer pondweeds,
• do not prefer plants such as cattail, water lily, etc.
Polyploidy Summary
• More than 2 whole sets of chromosomes,
• Autopolyploidy,
– from the same genome,
– naturally occurring, or induced,
– often results in larger varieties,
• Allopolyploidy,
– from different genomes,
– naturally occurring, or induced,
– often results in larger varieties,
• Autotriploids,
– most often sterile
– can produce beneficial traits.
Monoploidy
…a haploid of a diploid is monoploid,
…has one chromosome set.
Monoploid
• male wasps, bees and ants have only 1
haploid genome,
– males develop from unfertilized eggs,
• gametes are formed by mitosis.
Monoploid Applications
• monoploid plants can be created by
culturing pollen grains (n = 1),
– the population of haploid organisms is then
screened for favorable traits,
– the plants are then treated with colchicine
which generates a 2n plant homozygous for the
favorable traits.
Chromosomal Mutations
– chromosome number,
– structure,
Chromosome Structure
• Changes in chromosome structure can come
about due to,
deletions
duplications
rearrangements
Chromosomal Deletions
• a deletion results in a lost portion of a
chromosome,
Deletion Causative Agents
heat,
radiation,
viruses,
chemicals,
errors in recombination.
Terminal Deletions
Off the End
Intercalary Deletions
From the Middle
Intercalary Deletions
From the Middle
Recognizing Deletions
Terminal
Intercalary
Homologous Pairs?
Intercalary
Hemizygous
Terminal
Hemizygous: gene is present in a single dose.
Psuedodominance: hemizygous genes are expressed.
Deletions
…result in partial monosomy,
 remember monosomy: 2n, -1,
…the organism is monosomic for the portion
of the chromosome that is deleted,
…as in monosomy, most segmental deletions
are deleterious.
Cri-du-chat Syndrome
(46, -5p)
46, -5p
...terminal deletion of the small arm
(petite arm) of chromosome 5,
• Cri-du-chat Syndrome,
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0.002% live births,
anatomic mutations,
often mental retardation,
abnormal formation of vocal
mechanisms.
Chromosomal Duplication
...an event that results in the increase in the
number of copies of a particular
chromosomal region,
Duplication Cause and Effect
Causes:
– duplications often result from unequal crossing over,
– can occur via errors in replication during S-Phase.
Effects:
– results in gene redundancy,
– produces phenotypic variation,
– may provide an important source for genetic variability
during evolution.
Unequal Crossing Over
Produces both duplications and deletions!
Duplication Phenotypes
Duplication in Evolution
…essential genes do not tolerate mutation,
…duplications of essential genes, then
subsequent mutations, confers adaptive
potential to the organism,
…new gene family members are ‘recruited’ to
perform new functions.
flowering plant
algae
moss
nutrients
need uptake
need uptake
need uptake
transport to other tissue
transport to other tissue
transport to seeds
Arabidopsis
Chromosome Structure
• Changes in chromosome structure can come
about due to,
deletions
duplications
rearrangements
Chromosomal Inversions
…inversion: aberration in which a portion of
the chromosome is turned around 180o.
Paracentric Inversion
...an inversion in which the centomere is not
included,
A
B
C
A
B
B
A
C
...a paracentric inversion does not change arm
length ratio.
Inversion Heterozygotes
…an organism with one wild-type and one
chromosome containing an inversion,
A
B
C
B
A
C
…not heterozygous for the genes, heterozygous
for the chromosomes.
Inversion Loop
no crossing over
Paracentric
Produces haploid gamete.
Paracentric
Produces gamete with inversion.
Paracentric
Produces a chromosome with two centromeres.
Nonviable gametes.
Dicentric
...a chromosome having two centromeres;
Non-Viable (gametes) Segregate
Dicentric/Ascentric
…results only when the crossing over occurs
within the region of the paracentric inversion,
Paracentric
No centromeres. Deletions.
Nonviable gametes.
Acentric
…a chromosome having no centromeres,
…segregates to daughter cells randomly, or is
lost during cell division,
…deletions impart partial monosomy.
Paracentric Outcomes
1 Normal Gamete, 1 Inversion Gamete, No Crossover Classes
Recombination is not inhibited, but recombinant gametes are
selected against.
Pericentric Inversion
...an inversion in which the centromere is
included,
A
B
C
A
C
B
...a pericentric inversion results in a change in
chromosome arm length.
Pericentric
Recombination and Inversions
• Paracentric and Pericentric;
– 1 Normal Gamete,
– 1 Inverted Gamete,
– No Crossover Classes = No Recombination,
Inversions select against recombinant gametes,
thus preserves co-segregation of specific alleles.
Inversions and Evolution
• Inversions ‘lock’ specific alleles together,
– all offspring get their alleles from either a wildtype, or inverted chromosome,
• If the ‘set of alleles’ is advantageous, the set
can be maintained in the population.
Assignment
• Understand the differences between
‘Interference’, and the suppression of
recombination resulting from inversions,
• Be able to recognize data, and predict
results given either case.
Chapter 5
• Do all of the practice questions.
Translocations
…translocation: aberration associated with
the transfer of a chromosomal segment to a
new location in the genome.
Terminal Translocation
Reciprocal Translocation
Translocation and Semi-Sterility
…semi-sterility; a condition in which a proportion of all
gametophytes (in plants) or zygotes (in animals) are
inviable.
• Up to 50% are inviable as a result of translocations.
Robertsonian Translocations
…the fusion of long arms of acrocentric
chromosomes,
Down Syndrome
• 95% of Down Syndrome individuals are a result of
Trisomy 21,
– the probability of having a second Down Syndrome child
is usually similar to the population at large,
• However, there is second cause of Down Syndrome
caused by a Robertsonian translocations that is
heritable.
Familial Down Syndrome
Assignment
• Do a Punnett Square or a Split Fork Diagram
of,
Parent 1: wild-type for Chromosomes 14, 21
x
Parent 2: heterozygous for 14q;21q translocation.
Hint
gametes
Assignment
(think about these...)
• Truncated Genes;
– genes that are no longer full length, due to a
mutation,
• Gene Fusions;
– genes that contain coding sequence from two
different genes, resulting from a chromosomal
mutation.
Syntenic
• Relationship of two or more loci found to
be linked in one species; literally “on the
same thread”.
• Conserved Synteny: state in which the
same two loci are found to be linked in
several species.
Cereals
Conserved Synteny
Description of DNA segments in which gene order is identical between species.
Trinucleotide Repeat Expansions
FMR1
Fragile X Mental Retardation 1
...GCGCGGCGGTGACGGAGGCGCCGC
TGCCAGGGGGCGTGCGGCAGCG...
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…CTGGGCCTCGAAGCGCCCGCAGCCA
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> 200
Fragile Site Mutations
Dosage Compensation
• X chromosomes in females provide twice
the genes, as in males,
– Drosophila: female genes are expressed at 50%
of the male levels,
– Mammals: one X chromosome in females is
silenced.
Canadian Cat Scientists Sees it First
Barr Body
Lyon Hypothesis
Mary Lyon; in humans, X
chromosomes from father
and mother are randomly
inactivated.
X Inactivation
Barr Body
The structure of the chromosome is altered.
X-Linked Mosaicism
Different cell lineages
contribute to different
body locations on the
body.
Epigenesis
• A change in gene regulation brought about without
a change in DNA sequence,
– often to the structure of the chromosome,
– or through modification of the nucleotide bases,
– or through post transcriptional regulation.
Chapter 5 Review
• know genotypes and phenotypes,
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trisomy,
monosomy,
inversions,
duplications,
deletions,
polyploidy,
dosage compensation.
• be able to predict heritability, and recognize datasets and infer the condition.
Monday
• Reciprocal Translocations,
• Mapping deletions,
• Review
• Work some problems.