Lecture 21 – Aberrant Ploidy
I. Aberrant euploidy
A. examples of differing ploidy
monoploid 1x
pentaploid 5x
diploid
2x
hexaploid
6x
triploid
3x
octaploid
8x
tetraploid
4x
B. in nature
- in plants (and less commonly, animals) – 30 – 35% of naturally occurring plant
species are polyploid.
- endopolyploidy – in many animals, some cells may be polyploid
II. Monoploidy – 1n, rare result of errors in cell division
A. Usually sterile
B. in some species, some individuals are monoploid
- males in social insects (ants, bees, wasps)
- males produced by parthenogenesis
- not sterile because
C. useful experimentally and in agriculture
- experimental use of monoploidy
- but how do you get back to diploid?
meiotic product
cells plated
monoploid
plant
(sterile)
diploid
plant
treat
with
colchicine
haploid
embryoids
diploid
embryoids
monoploid
plant
diploid
plant
grow haploid
plantlets
1
grow diploid
plantlets
III. Polyploids (odd vs. even chromosome #)
A. Odd ploidies
1. origins of triploid
A1
A3
A2
A1 A2 A3
- odd ploidies are generally sterile
-
why?
- triploidy can be very useful?
B. Even ploidies and cell divisions
- most natural polyploids are even in # homologues (i.e. 2x, 4x, 6x, 8x, etc)
IV. Auto vs allopolyploids
A. major types
1. autopolyploid
2. allopolyploid
- homeologous
2
B. autopolyploid
mitosis
meiosis
A1 A1
A2 A2
A1 A1
2n
2n
A2 A2
- endoreduplication
4n
0n
A1
A1
2n
0n
A1 A1
A2
A2 A2
A2
A1
A2
A1 A2
C. allopolyploidy
2n
0n 0n
2n
D. experimental allopolyploidy’
- way of producing useful plant varieties
tall fescue
Italian ryegrass
isolate cells
remove cell wall
fuse protoplasts
heterokaryon
hybrid cell
regenerate plant
allotetraploid
3
plant has characteristics
intermediate between
two parents
IV. Aneuploidy
A. polysomy
1. trisomy
a. consequences
b. human trisomies (most are inviable)
- Klinefelter (XXY)
- trisomy 21 (Down syndrome)
- trisomy 13 (Patau syndrome)
- trisomy 18 (Edwards syndrome)
2. monosomy
a. human monosomies
B. aneuploidy arises because of nondisjunction during meiosis
a
A
a
A
b
B
A
b
B
A
a
b
b B
B
A
a
A
b
B
a
b
B
4
a