2. 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.
3. • . 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 .
4. ALLOPOLYPOLIDY
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 .
5. 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).
6. Triticum urartu (AA) Aegilops speltoides (BB)
T. turgidum (AABB) T. tauschii (DD)
T.astivum
AABBDD
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 tetraploid
intermediary (durum wheat).
7. Allopolyploidy in Animals
• In animals, allopolyploidy is rare. Allopolyploidy was found in
insects, fish, reptiles, and amphibians. For example, Xenopus
laevis, 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.
8. 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
9. Characteristics of Allopolyploids
• Larger cells
• Vigorous plant
• Less complex than autopolyploids
• Recessive characters may appear less frequent
10. species A
species B
X
Hybrid AB
during meiosis
aborted gamete
production
Hybrid AB
body cells
spontaneous
genome
duplication
Duplicated genomes are fertile !!
Botanical term: Allopolyploids
Hybrid AABB
“allopolyploid”
successful cell division
(fertile)
Allopolyploidy arises from hybridization plus
genome duplication
12. 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
13. The cabbage family: “Triangle of U”
Black mustard
N=8
N=10+8
BB
Brassica carinata Brassica juncea
Chinese cabbage, Bok Choi
Cauliflower, broccoli, kale
Qu i ckTi me™ an d a
TIFF (Uncompres sed) decompres sor
are needed to see this picture.
N=9 N=10
rape seed
Indian mustard
Canola-type oil seeds
Collard green,
good for cold
climates
biodiesel
Brassica nigra
N=10+9
Brassica olarecea Brassica napus
Brassica rapa
AABB
AA
BBCC
AAC
C
N=9+8
CC
picture sources: various www.
