ALLOPOLYPLOIDALLOPOLYPLOIDS

Group No 34TH (D)

POLYPLOIDY

• Polyploidy = the addition of one or more complete sets of chromosomes to the original set.

• two copies of each autosome = diploid

• four copies of each autosome = tetraploid

• six copies of each autosome = hexaploid

• The gametes of diploids are haploid, those of tertraploids are diploid, those of hexaploid are triploid, and so on.

• . Two main types of polyploidy: • autopolyploidy (genome doubling) =

the multiplication of one basic set of chromosomes

• allopolyploidy = the combination of genetically distinct, but similar chromosome sets.

• Autopolyploids are derived from within a single species; allopolyploids arise via hybridization between two species .

ALLOPOLYPOLIDYautopolyploidy (genome doubling) = the multiplication of one basic set of chromosomesallopolyploidy = the combination of genetically distinct, but similar chromosome sets.

Autopolyploids are derived from within a single species; allopolyploids arise via hybridization between two species .

Allopolyploidy is much more common in nature than autopolyploidy. About 80% of all land plants may be allopolyploids.

Red circles indicate instances of allopolyploidy. The blue circle indicates an instance of autopolyploidy. The green square indicates a putative triplication event before the divergence among dicotydelons. The two black ovals indicate an ancestral angiosperm genome duplication (190-230 million years ago) and an ancestral seed-plant duplication (320-350 million years ago).

Triticum urartu (AA) Aegilops speltoides (BB)

T. turgidum (AABB) T. tauschii (DD)

T.astivumAABBDD

The common bread wheat (Triticum aestivum) is an

allohexaploid containing three distinct sets of chromosomes derived from three different diploid species of goat-grass

(Aegilops) through a tetraploidintermediary (durum wheat).

Allopolyploidy in Animals

• In animals, allopolyploidy is rare. Allopolyploidy was found in insects, fish, reptiles, and amphibians. For example, Xenopuslaevis, the African clawed frog of laboratory fame, is an allotetraploid. No cases of polyploidy have ever been found in birds. Two mammalian species are suspected tetraploids, the red vizcacha rat (Tympanoctomys barrerae) and the golden vizcacha rat (Pipanacoctomys aureus), however, some disagreement exists in the literature.

Identifying Auto- & Allopolyploidy

Autopolyploids typically have

multivalent pairing

- chromosomes are more or less

identical

Allopolyploids are variable

- bivalent pairing with more genetic

divergence

- multivalent pairing when closely

related

Characteristics of Allopolyploids

• Larger cells

• Vigorous plant

• Less complex than autopolyploids

• Recessive characters may appear less frequent

species A

species BX

Duplicated genomes are fertile !!Botanical term: Allopolyploids

aborted gamete production

Hybrid AB

body cells

Hybrid AB

during meiosis

spontaneousgenome

duplication

(fertile)

successful cell division

Hybrid AABB

“allopolyploid”

Allopolyploidy arises from hybridization plus genome duplication

Allopolyploids in Plant Breeding

Allopolyploids in Plant Breeding

• Identify genetic origin of plant species

• Produce new plant genotypes and plant species

• Facilitate transfer of genes from related species

• Facilitate transfer of individual chromosomes or pairs of chromosomes

The cabbage family: “Triangle of U”

Black mustard

Chinese cabbage, Bok Choi

Cauliflower, broccoli, kale

QuickTime™ and aTIFF (Uncompres sed) decompres sor

are needed to see this p ictu re .

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.