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Characteristics of Allopolyploids
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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.