1. Polyploidy in Plants: Formation, Types, Examples by Andreas Madlung and Luca Comai
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2. I. Autopolyploidy arises from genome duplication
species A X
species A
Autopolyploidy arises from the duplication of the chromosomes in the genome of a species A. This can occur spontaneously when a cell goes through regular mitosis but by accident omits cytokinesis (cell division). Many agricultural plant species are autopolyploids, such as lettuce and certain varieties of strawberries.

3. I. Autopolyploidy arises from genome duplication
species A X
species A
diploid
(fertile)

4. I. Autopolyploidy arises from genome duplication
species A X
species A
diploid
(fertile)
spontaneous
genome
duplication
autotetraploid
(fertile)
Autopolyploids are fertile because each chromosome has a partner with which it can pair during meiosis, the process in which gametes are produced. Duplicated genomes are tetraploid when the cell contains 4 copies of each chromosome. It is diploid when it contains only 2 copies of each. Autopolyploidy in some plants can result in cells with more than a hundred chromosomes.

5. I. Autopolyploidy arises from genome duplication
species A X
species A
diploid
(fertile)
spontaneous
genome
duplication
autotetraploid
(fertile)
Causes of genome duplication:
a) meiotic non-reduction of gametes (both in egg and sperm)
b) genome duplication w/o cytokinesis (after fertilization)
There are two major causes of genome duplication:
meiotic non-reduction of gametes, which can occur in both egg and sperm cells leading to diploid gametes or genome duplication of somatic cells w/o cytokinesis (after fertilization)

6. Duplicated genomes are fertile !! Botanical term: Allopolyploids
II. Allopolyploidy arises from hybridization plus genome duplication
species A
species B X
Hybrid AB
body cells
Hybrid AB
during meiosis
(fertile)
successful cell division
Hybrid AABB
“allopolyploid”
spontaneous
genome
duplication
aborted gamete production
Allopolyploids are plants that arise from the hybridization of two different species and subsequent genome duplication. Diploid hybrids are usually sterile because during meiosis when homologous chromosomes normally pair up, diploid hybrid cells have no proper homologues that can pair with each other. The cell recognizes the lack of proper pairing and halts the cell cycle, leading ultimately to aborted gamete production. If spontaneous duplication of the genome occurs, each resulting duplicate chromosome can act as a homolog during meiosis and lead to normal gamete production.
Duplicated genomes are fertile !! Botanical term: Allopolyploids

7. species A X species B II. Allopolyploids are special kinds of hybrids
sterile
Genome
duplication
fertile
III. Homologous pairing is predominant in allopolplyoids
In allopolyploids, chromosome pairing usually results in normal meiosis. Crossing over between chromosomes of the two different original parent species (known as homeologous chromosomes) is rare.

8. IV. Homologous pairing is predominant in allopolplyoids
homeologous pairing
homologous 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
Nomenclature for polyploids is based on the so-called basic chromosome number X. This number is the number of chromosomes one would find in a diploid individual of this species. The gametic number is abbreviated as N and describes the number of chromosomes in egg or sperm cells, while the somatic chromosome number is the number of chromosomes found in body cells.

9. VI. Diploid vs. Allopolyploid hybridization
selfing generations
genomes maintained separately
Crossing over in heterozygous diploids (of the same species) slowly leads to homozygosity over many generations (shown by multiple arrows). Allopolyploids keep their chromosomes separate from each other and only over evolutionary time show decay of genes through mutation and/or change of gene functions via subfunctionalization.

10. A. thaliana red probe A. arenosa green probe
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 green probe
A technique commonly used to identify specific regions of a chromosome is called fluorescent in situ hybridization. Here, a probe is made by a process similar to PCR that incorporates fluorescent nucleotides into the probe DNA. When hybridized to a chromosome preparation on a microscope slide, the probe made to a specific stretch of chromosome, will find its complement and bind, lighting up the chromosome when viewed using fluorescent microscopy. Popular FISH probes are those made to the centromere. Centromeric probes often bind to all chromosomes of the same species. However, they are specific to the species and can therefore help distinguish the origin of chromosomes in hybrids of different parents.
Centromeric probe

11. What is the genomic composition of allopolyploid hybrids of A
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
Here are three examples of FISH analysis using two probes against centromeric regions of the two species Arabidopsis thaliana and A. arenosa. In meiotic spreads of allopolyploids of these two species, the original chromosomes can easily be distinguished. Here during Anaphase, centromeres are facing each other just before being pulled to the poles by the spindle fibers. Material stained blue in these pictures is DNA not bound by a probe.
Pollen mother cells: early Anaphase I
sample 3
Comai et al., Chrom. Research, 2003

12. Allopolyploidy may lead to speciation Example: Speciation in the cabbage family
Black mustard
Collard greens BB
Brassica nigra
BBCC
Indian mustard
AABB
Brassica carinata
Brassica juncea
On this and the next slide are two ways to show the “triangle of U”. This triangle, first described by the Korean scientist Nagaharu U, shows how three diploid species of Brassica have formed allopolyploid intermediates. Many of the species in the triangle of U are well-known agricultural plants of the cabbage family. CC
AACC AA
Brassica olarecea
Brassica napus
Brassica rapa
Cauliflower, broccoli, kale
rape seed
Chinese cabbage, Bok Choi
picture sources: various www.

13. The cabbage family: “Triangle of U”
Black mustard
Chinese cabbage, Bok Choi
Cauliflower, broccoli, kale
rape seed
Indian mustard
Canola-type oil seeds
Collard green, good for cold climates
biodiesel
Brassica nigra
Brassica rapa
Brassica olarecea
Brassica carinata
Brassica juncea
N=8
N=9
N=10
N=10+8
N=10+9
Brassica napus BB
AABB AA
BBCC
AACC
N=9+8 CC
picture sources: various www.

14. In some cases allopolyploid speciation is a recurring phenomenon Example: Tragopogon
Tragopogon dubius
2N=12
Tragopogon miscellus
2N=24
Tragopogon mirus
2N=24
Another example of allopolyploidization leading to evolutionary change is that of Tragopogon or Goat’s beard. Native to eastern Washington state, allopolyploidization in Tragopogon has been shown to occur frequently and on a recurring basis.Tragopogon allopolyploids show intermediate phenotypes.
Tragopogon porrifolius 2N=12
Tragopogon pratensis 2N=12
picture credit: