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 diploid(fertile)

X

I. Autopolyploidy arises from genome duplication

species A

species A diploid(fertile)

X

autotetraploid(fertile)

spontaneousgenome duplication

I. Autopolyploidy arises from genome duplication

species A

species A diploid(fertile)

X

autotetraploid(fertile)

spontaneousgenome duplication

Causes of genome duplication:a) meiotic non-reduction of gametes (both in egg and sperm)

b) genome duplication w/o cytokinesis (after fertilization)

species A

species BX

Duplicated genomes are fertile !!Botanical term: Allopolyploids

aborted gamete production

Hybrid ABbody cells

Hybrid ABduring meiosis

spontaneousgenome duplication

(fertile)

successful cell division

Hybrid AABB“allopolyploid”

II. Allopolyploidy arises from hybridization plus genome duplication

II. Allopolyploids are special kinds of hybrids

species A

species BX

III. Homologous pairing is predominant in allopolplyoids

sterile fertileGenome duplication

homologous pairing homeologous pairing

IV. Homologous pairing is predominant in allopolplyoids

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

A. arenosagreen probe

A. thalianared probe

Species-specific fluorescent probes made to two species: Arabidopsis thaliana and A. arenosa

Centromeric probe

Centromeric probe

What is the genomic composition of allopolyploid hybrids of A. thaliana and

A. arenonsa ?

Comai et al., Chrom. Research, 2003

sample 1

sample 2

sample 3

Allopolyploid cells

FISH: fluorescent in situ hybridizationred: A. th centromeric repeatgreen: A. are centromeric repeatblue: chromosome arms (DAPI stained)

Pollen mother cells: early Anaphase I

Black mustard

Chinese cabbage, Bok Choi

Cauliflower, broccoli, kale

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

rape seed

Indian mustard

Collard greens

Brassica nigra

Brassica rapa

Brassica olarecea

Brassica carinata Brassica juncea

Brassica napus

BB

AABB

AAAACC

BBCC

CC

picture sources: various www.

Allopolyploidy may lead to speciationExample: Speciation in the cabbage family

The cabbage family: “Triangle of U”

Black mustard

Chinese cabbage, Bok Choi

Cauliflower, broccoli, kale

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

rape seed

Indian mustardCanola-type oil seeds

Collard green, good for cold climatesbiodiesel

Brassica nigra

Brassica rapaBrassica 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.

In some cases allopolyploid speciation is a recurring phenomenon

Example: Tragopogon

picture

credit:http://www.botany.org/plantimages

Tragopogon dubius2N=12

Tragopogon miscellus2N=24

Tragopogon pratensis 2N=12

Tragopogon mirus2N=24

Tragopogon porrifolius 2N=12

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture. QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.