Polyploidy in Plants:
Formation, Types, Examples
by Andreas Madlung and Luca Comai
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I. Autopolyploidy arises from genome duplication
species A
species A
X
I. Autopolyploidy arises from genome duplication
species A
species A
X
diploid
(fertile)
I. Autopolyploidy arises from genome duplication
species A
species A
X
diploid
(fertile)
spontaneous
genome
duplication
autotetraploid
(fertile)
I. Autopolyploidy arises from genome duplication
species A
species A
X
diploid
(fertile)
spontaneous
genome
duplication
Causes of genome duplication:
a) meiotic non-reduction of gametes (both in egg and sperm)
b) genome duplication w/o cytokinesis (after fertilization)
autotetraploid
(fertile)
II. Allopolyploidy arises from hybridization plus
genome duplication
species A
Hybrid AB
body cells
species B
Hybrid AB
during meiosis
Hybrid AABB
“allopolyploid”
X
spontaneous
genome
duplication
aborted gamete
production
Duplicated genomes are fertile !!
Botanical term: Allopolyploids
successful cell division
(fertile)
II. Allopolyploids are special kinds of hybrids
species A
species B
X
sterile
Genome
duplication
III. Homologous pairing is predominant in
allopolplyoids
fertile
IV. Homologous pairing is predominant in
allopolplyoids
homologous pairing
homeologous pairing
V. Nomenclature for autopolyploids
Base number of chromosomes: X
Humans: X=23
Gametic number: N
Humans: N=23
Somatic number: 2N
Humans: 2N=2X-46
VI. Diploid vs. Allopolyploid hybridization
selfing generations
genomes maintained separately
Fluoresecent In Situ Hybridization (FISH) analysis
can identify progenitor chromosomes
Species-specific fluorescent probes made to two species:
Arabidopsis thaliana and A. arenosa
A. thaliana
red probe
Centromeric probe
A. arenosa
Centromeric probe
green probe
What is the genomic composition of allopolyploid
hybrids of A. thaliana and A. arenonsa ?
Allopolyploid cells
sample 1
FISH: fluorescent in situ hybridization
red: A. th centromeric repeat
green: A. are centromeric repeat
blue: chromosome arms (DAPI stained)
sample 2
Pollen mother cells: early Anaphase I
sample 3
Comai et al., Chrom. Research, 2003
Allopolyploidy may lead to speciation
Example: Speciation in the cabbage family
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Black mustard
Collard greens
BB
Brassica nigra
Indian mustard
BBCC
AABB
Brassica carinata
CC
AACC
Brassica olarecea
Cauliflower, broccoli, kale
picture sources: various www.
Brassica juncea
rape seed
Brassica napus
AA
Brassica rapa
Chinese cabbage, Bok Choi
The cabbage family: “Triangle of U”
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Black mustard
N=8
Collard green,
good for cold
climates
biodiesel
BB
Brassica nigra
N=9+8
N=10+8
BBCC
AABB
Brassica carinata
N=9
CC
Cauliflower, broccoli, kale
rape seed
picture sources: various www.
Brassica juncea
N=10+9
Brassica olarecea
Indian mustard
Canola-type oil seeds
AAC
Brassica
napus
C
N=10
AA
Brassica rapa
Chinese cabbage, Bok Choi
In some cases allopolyploid speciation is a recurring
phenomenon
Example: Tragopogon
Tragopogon dubius
2N=12
Tragopogon miscellus
2N=24
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Tragopogon pratensis 2N=12
Tragopogon mirus
2N=24
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Tragopogon porrifolius 2N=12